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Evaluation of coastal and marine ecosystem services of Mayotte: Indirect use values of coral reefs and associated ecosystems

Evaluation of coastal and marine ecosystem services of Mayotte: Indirect use values of coral... INTERNATIONAL JOURNAL OF BIODIVERSITY SCIENCE, ECOSYSTEM SERVICES & MANAGEMENT, 2017 VOL. 13, NO. 3, 19–34 https://doi.org/10.1080/21513732.2017.1407361 SPECIAL ISSUE: OPERATIONALISING MARINE AND COASTAL ECOSYSTEM SERVICES Evaluation of coastal and marine ecosystem services of Mayotte: Indirect use values of coral reefs and associated ecosystems a,b a c Ewan Trégarot , Pierre Failler and Jean-Philippe Maréchal a b Portsmouth Business School, University of Portsmouth, Portsmouth, UK; Observatoire du Milieu Marin Martiniquais, Schoelcher, Martinique, France; Nova Blue Environment, Schoelcher, Martinique, France ABSTRACT ARTICLE HISTORY 2 2 2 Received 30 September 2016 Coral reefs of Mayotte (342 km ), seagrass beds (7.6 km ) and mangroves (8.5 km ) provide Accepted 14 November 2017 important ecosystem services of which the most important are the coastal protection, fish biomass production, carbon sequestration and water purification. The quantity and quality of EDITED BY these services have been decreasing steadily for several years and should continue to do so if Sebastian Villasante no action is taken to contain anthropogenic pressures. The coral cover of the fringing reefs KEYWORDS and the barrier reef has thus declined, respectively, by 60% in 15 years and 15% in 8 years. Indirect use values; The pioneer front of Sonneratia for mangroves has declined by 13% in 6 years, and for ecosystem services; coral seagrass beds, the water quality suggests a degraded state. The estimated annual value of reefs; mangroves; seagrass these services amounts to EUR 124 million. It would be EUR 162 million if the ecosystems beds; Mayotte; Indian Ocean were in pristine conditions. The article shows that the preservation of coastal ecosystems is essential from an economic point of view. Introduction Fieldwork was carried out in 2014 and 2015 in Coral reefs are among the most productive marine eco- Mayotte. The territory acquired the status of French systems, especially in terms of biodiversity (Wilkinson overseas department and region in 2011. The last census 2008). On a global scale, a fifth has been destroyed and counted 235,132 inhabitants (INSEE 1975–2017)for an half of the remaining reefs are endangered (Wilkinson area of 376 km , making Mayotte the overseas depart- 2008;Burke et al. 2011;Bridgeetal. 2013;Hoegh- ment with the highest population density (625 people Guldberg 2014). Beyond their ecological importance per km ). (habitats, spawning areas, etc.) and coastal protection The aim of the article is to present the monetary dimension, coral reefs and associated ecosystems (sea- value of IUV relative to the ecological services pro- grass beds, mangroves and mudflats) have important vided by CRAE of Mayotte. These services such as economic and social scopes in the French overseas terri- coastal protection, production of fish biomass, water tories, particularly for fishing, tourism and recreation. purification and carbon sequestration are not sub- Since 2006, the French Government has implemen- jected to market exchanges. ted a programme to evaluate the total economic value Schröter et al. (2005) stated: ‘an increase in the (TEV) of coral reefs and associated ecosystems (CRAE) habitats vulnerability is likely to decrease the supply of all French overseas territories, through the French of ecosystems’. The assessment of marine habitats Coral Reef Initiative (IFRECOR). A methodology was vulnerability has become important to point out developed and approved by the ministry of the envir- anthropogenic threats (Halpern et al. 2007) and eval- onment. These guidelines have been included in the uate marine habitats ecosystem services potential terms of reference for the Mayotte assessment. based on vulnerability approaches (Bouahim et al. Assessment is done following the methodology detailed 2015, Cabral et al. 2015). The article relates an aspect in the guidelines produced by Maréchal et al. (2014)asa rarely considered in the evaluation of coastal ecosys- part of IFRECOR. The TEV expressed in euro/year, tem services, namely the integration of ecosystem sums up the use values (UV), the indirect use values health status in the weighting of production func- (IUV) and the non-use values (NUV). Use values are tions. A healthy ecosystem provides a full range of related to leisure activities such as bathing and diving or services, the capacity of which decreases as and when commercial uses such as commercial fishing. Indirect it is disturbed, polluted, weakened, etc. In other use values concern regulating ecological functions. words, a healthy ecosystem produces ecological ser- Non-use values refer to the spiritual dimension and vices that are quantitatively and qualitatively higher existence of the nature (Corvalan et al. 2005). than the same ecosystem in poor condition. The CONTACT Ewan Trégarot ewan.tregarot@gmail.com © 2017 The Author(s). Published by Informa UK Limited, trading as Taylor & Francis Group. This is an Open Access article distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/4.0/), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited. 20 E. TRÉGAROT ET AL. Marine science institute of Martinique (Observatoire services: coastal protection against erosion, coastal water purification, atmospheric carbon sequestration and fish du Milieu Marin Martiniquais – OMMM) has devel- oped, as part of the ecological monitoring of the biomass production (of which a portion also forms a coastline (Legrand et al. 2008), a method calibrating provisioning service for fisheries). It is considered that for coastal protection (given the health status of coastal marine ecosystems for Martinique, which is applied here. The article casts the juxtaposition of natural barrier reefs in Mayotte): additional light on how to take into account this key The outer barrier reef (208 km – Thomassin environmental variable in assessing coastal ecological et al. 1989) ensures global coastal protection, services. The inner reefs (inner barrier and fringing reef), The article is structured in four parts. In the first seagrass beds and mangroves have ‘optional’ part materials and methods for the valuation of eco- coastal protection value most of the time, but system services of coastal protection, carbon seques- are not negligible in case of exceptional weather tration, water purification and biomass production events. are presented. In the second part, the results show Carbon sequestration is not taken into account for the health status of Mayotte coastal ecosystems then, coral reefs because of lack of data. Indeed, coral calcifi- selected production functions are described before cation as a carbon storage process is tangible because addressing the weighting factors to refine the level one must consider organisms’ respiration and coral of services provided. From these elements, a mone- dissolution for which CO is thus recirculated into the tary valuation of IUV is proposed taking into account atmosphere (Shaw et al. 2015). Table 1 summarises the the weighting factors of ecosystem health status. In production functions selected for the CRAE of Mayotte. the third part, a discussion is offered on the most important aspects to remember, especially those that contribute to the development of public policy. A conclusion summarises the determining elements. Ecosystem mapping and health status assessment Wickel and Thomassin’s(2005) fringing coral reefs map and PARETO’s(2013) barrier reefs map allow Materials and methods estimation of the ecosystem surfaces (mandatory for The valuation of ecosystem services was conducted in valuation of water purification and biomass produc- Mayotte using the method developed by Maréchal tion services) and the linear length of each ecosystem et al. (2014) under the IFRECOR framework on along the coastline (mandatory for calculation of the ‘Socio-economic valuation’. It follows five stages: (1) coastal protection service). The health status of coral identification of ecological ecosystem services linked reef was assessed based on alive coral cover percen- to indirect uses, (2) ecosystem mapping and health tage compared to the total reef areas. Mangroves fine status assessment, (3) definition of production func- mapping study from Jeanson (2009) was used to tions and assessment of produced services, (4) appli- characterise salt marshes, rear mangrove, central cation of a weighting coefficient and (5) and inner foreshore mangroves and pioneer fronts determination of indirect use (monetary) values. of Sonneratia alba, a species of mangrove. The health status of mangroves was assessed according to their vulnerability classification, established under the eva- Identification of ecological ecosystem services luation criteria of the Red List of French ecosystems The identification of ecological services linked to indir- (UICN 2015). Discussions with members of the ect uses follows the Millennium Ecosystem Assessment National Forestry Commission and the UICN during classification (Corvalan et al. 2005). A review of Mayotte the meeting to validate the vulnerability criteria marine and coastal biodiversity literature was conducted allowed clarification on the methodology. The to collect information on coastal habitat maps prior to Department of Agriculture and Forestry (2006) pro- fieldwork (Wickel and Thomassin 2005; Jeanson 2009; duced a map for seagrass beds. No data on seagrass Herteman 2010; Jamon et al. 2010;PARETO 2013). The health status was available at the time of this study. ecosystem services selected for Mayotte are regulation We estimated seagrass beds status using Mayotte Table 1. Selected ecosystem services for marine coastal ecosystems of Mayotte (Indian Ocean). Coral reefs Services Outer barrier Inner barrier Fringing reef Mangroves Seagrass Coastal protection ✔ Option Option Option Option Water treatment ✔✔ ✔ Carbon sequestration NA ✔✔ Biomass production ✔✔ ✔ NA: non-applicable production function; Option: indicates an optional production function. INTERNATIONAL JOURNAL OF BIODIVERSITY SCIENCE, ECOSYSTEM SERVICES & MANAGEMENT 21 water bodies assessment under the EU Water respectively, to 14 and 15% of the carbon storage Framework Directive (PARETO, ASCONIT 2013). capacity of the oceans (Laffoley and Grimsditch 2009; Waycott et al. 2009; Donato et al. 2011). The respective net productivities of Sonneratia/ Definition of production functions and Avicennia and Rhizophora mangrove communities assessment of produced services are 9.54 tC/ha/year and 10.5 tC/ha/year Ecosystem services estimation relies on ecosystems (Poungparn and Komiyama 2013). These values surface data, assessment of their health status and are applied to Mayotte mangroves. The estimated net productivity of seagrass beds is maximum production level for each service (Table 2). While coastal protection, carbon sequestration and 1.19 tC/ha/year (Duarte et al. 2010), equivalent to 435 biomass production services benefit from extended tCO eq/km /year on average. This later value is references, water purification valuation is based only applied to Mayotte case study. on Costanza et al. (1997) monetary reference despite the absence of reference work to validate this result. Water purification Water purification is the absorption capacity of nutri- Coastal protection ents by ecosystems in relation to their surface and The coastal protection service mitigates extreme health status. Coral reefs have very low capacity of weather events such as tsunami or hurricane swells water purification, but the coral – algal shift in coral (Kunkel et al. 2006). The reef structures absorb up to reefs increases the water purification function accord- 90% of the waves energy (Ferrario et al. 2014). If ing the intensification of algae cover. extreme natural conditions threaten the coastline of The capabilities of bio-remediation of mangrove Mayotte, the inner barrier reef, the fringing reef, forests were assessed at Malamani (Herteman 2010) seagrass beds and mangroves would absorb most of and studies are still under progress. This study shows the waves’ energy left. Only two sectors in Mayotte that wastewaters are partly absorbed by the aremoresensibletocyclonicswell giventhe direc- vegetation. tion of waves that may enter the lagoon through reef Seagrass meadows can trap nutriment-loaded sedi- pass: Pointe Kani in the south and Tsingoni bay on ments, acting as coastal water filters (Duarte 2000). the west coast where waves’ height can remain Besides, seagrass plants absorb dissolved minerals greater than 1 m while for the rest of Mayotte and nutrients for their own growth directly from coast, waves’ height is less than 50 cm (Lecacheux water. et al. 2007). Seagrass beds stabilise the sediment and reduce waves’ energy by about 40% (Fonseca and Cahalan 1992; Christianen et al. 2013). The last Biomass production physical barriers, composed of mangrove forests, Coral reefs provide habitat and nursery grounds for dissipate wave energy and significantly diminish many fish species and represent very important fish- wave height over very short distances (Jeanson ing areas for the local population. The pioneer fronts 2009). Mangrove trees Sonneratia sp.characterise of Sonneratia alba communities are submerged by the pioneer front of mangroves and absorb about seawater and house fifty-eight species of fish 50% of wave energy over a distance of 100 m (Mazda (Ponton et al. 2013). Seagrass areas also form nursery et al. 2006). grounds for juvenile fish that use the dense canopy as a shelter during early life stages (Pogoreutz et al. Carbon sequestration 2012). Other larger species use seagrass beds as tran- Mangroves and seagrasses ecosystems form signif- sition area to feed and hunt (Unsworth et al. 2008), icant carbon sinks and each contribute, and are targeted by fisheries. Table 2. Production functions and services estimation. Indirect use service Definition Data used for services estimation Coastal protection Ecosystem’s ability to reduce wave power/energy ● Coastline/surface area of ecosystems playing a protection role ● Coefficient of wave power attenuation provided by ecosystem ● Health status of ecosystems Water treatment Ecosystem’s ability to absorb nutrients ● Area of ecosystem playing a water treatment role ● Health status of ecosystems Carbon storage Ecosystem’s ability to absorb atmospheric or dissolved carbon ● Area of ecosystem ● Average carbon absorption rate of ecosystem ● Health status of ecosystems Biomass production Ecosystem’s ability to produce exploitable fish biomass ● Biomass production rate of ecosystem ● Portion of marketable and exploitable species 22 E. TRÉGAROT ET AL. canopy height and density of plants/trees are often The fish biomass production (of which a por- used (Dirberg 2015; Taureau et al. 2015). tion forms also a provisioning service as part of the biomass is subject to fishing) represents the ecosystem ability to produce exploitable fish Determination of indirect use monetary values biomass. Determining indirect use monetary value is specific to each service and ecosystem. Carbon sequestration and production of fish biomass valuation use, respec- Application of a weighting coefficient tively, the price market of a tonne of CO and kilo- Production functions are weighted according to the gram for fish. Water purification and coastal estimated amount of service provided by the ecosys- protection functions are evaluated according to repla- tem. Health status indexes and levels of vulnerability cement cost and value transfer methods. The value of marine environments are elaborated from pub- transfer method was used to provide economic value lished references. They are applied to a production of ecosystem services through a simple approach function that would provide 100% of the service. usable in different contexts and for comparison. The coastal protection service provided by coral This methodology, although questionable, was reefs is weighted by their health conditions (Wickel retained in the IFRECOR terms of reference for this and Thomassin 2005; PARETO 2013) and the meth- study, essentially because it can be easily adjustable to ods from Sheppard et al. (2005) and Ferrario et al. any case study. Coastal linear length ecosystem and (2014), considering that: gross domestic product (GDP) are basically the only A 100% mortality of live corals in coral reefs data necessary to obtain a gross estimate. This article leads to an average 10% decrease of the waves provides guidance for conducting and refining such attenuation effect; value transfers to facilitate its application despite the The outer barrier absorbs up to 91% of the wave various constraints that make primary data collection power; impractical. A linear model correlates coral reef health status The coastal protection service value is calculated and wave attenuation; using the method of costs replacement by artificial The width of the reef flat influences the attenua- breakwater-like structures such as: tion of the remaining wave power. PC ¼ðÞ C  E  PIB  T =PIB (1) i i i m i r The width of the reef flat is 1150 m for the outer barrier (between 800 and 1500 m) and 425 m for the with: fringing reef (between 50 and 800 m) (Jeanson 2009). PC = value of coastal protection for ecosystem i The average width of the inner barrier reef flat, mea- (€/year), sured from 18 measurements of aerial images (Google C = cost of producing a man-made structure Earth) is 360 m. providing the same service of coastal protection as Ecosystem vulnerability categories established by ecosystem i (€/km/year or €/km /year), the UICN (2015) for mangroves were used to weight E = coastline or surface of ecosystem i (km mangrove services of Mayotte: 20, 40, 60, 80 and or km ), 100%, respectively, for habitat critically endangered PIB = GDP/capita of Mayotte (€), (CR), endangered (EN), vulnerable (VU), near threa- PIB = GDP/capita of reference study area (€) and tened (NT) and of least concern (LC). T = type of protection provided by ecosystem The European Water Framework Directive (WFD) (between 0 and 1 for service provided, respectively, recommendation on seagrass beds classification was between 0 and 100%). used for the weighting of ecosystem services. Five The water treatment value is obtained from the health status categories are used to assess ecosystem estimated replacement cost of coastal waters natural (bad, poor, moderate, good and high) to which will purification functions by technological artefacts be associated the respective weighting coefficients 20, such as: 40, 60, 80 and 100%. TE ¼ðÞ C  E  PIB =PIB (2) i i i m r Weighting of ecosystem services of CRAE by health status is poorly developed in the literature with: and few indicators are available to estimate the health TE = value of water treatment provided by eco- status of coral reefs, mangroves and seagrass beds. system i in Mayotte (€/year), WFD indicators have been created or are under C = water treatment reference value per unit of development (Le Moal and Aish 2013; Dirberg area of ecosystem i (€/km /year), 2015). For coral reefs ecosystems, coral and macro- E = total surface area of ecosystem i providing a algae covers are the major variables (Le Moal and type of water treatment (km ), Aish 2013), while for mangroves and seagrass beds, PIB = GDP/capita of Mayotte (€) and m INTERNATIONAL JOURNAL OF BIODIVERSITY SCIENCE, ECOSYSTEM SERVICES & MANAGEMENT 23 PIB = GDP/capita of reference study area (€). B = average biomass production per unit area for r i The value of carbon sequestration services is ecosystem i, obtained by estimating the amount of carbon assimi- T = portion of marketable and exploitable species lated by the ecosystem multiplied by the average price (between 0 and 1), of a tonne of CO according to the following E = total area of ecosystem i and 2 i equation: VA = average value added per kilo of fish for the considered region. SQ ¼ A  E  PCO (3) i i 2 with: SQ = value of carbon sequestration for ecosystem i Results (€/year), Marine ecosystems mapping A =CO absorption rate for ecosystem i 2 i(tCO /km /year), Coastal ecosystems of Mayotte consist of coral reefs, E = total area of ecosystem i (km ) and mangroves and seagrass beds with respective areas of 2 2 PCO = average price of a tonne of CO (€). 342 km (Andréfouët et al. 2008), 8.5 km (UICN 2 2 The production of fish biomass is calculated from 2015) and 7.6 km (Loricourt 2005 – see Figure 1). the estimated value of catchable (and marketable) Coral reefs comprise barrier reefs (266 km – 208 km), biomass using the following equation: fringing reefs (47 km – 195 km) and internal lagoon reefs (30 km – 18 km) forming a double barrier in the PB ¼ B  T  E  VA (4) i i i i southwest of the island (Guilcher et al. 1965; with: Thomassin et al. 1989; Wickel and Thomassin 2005; PB = biomass production value for ecosystem i Andréfouët et al. 2008). The large area of coral reefs of (€/year), Mayotte comes from the geological history of the Figure 1. Geographical distribution of CRAE of Mayotte – Modified from Gigou et al. (2009). Copyright 2017 by Agence des Aires Marines Protégées. Adapted with permission. 24 E. TRÉGAROT ET AL. island and the subsidence effect (sinking of the island large surfaces during proliferation outbreaks under its own weight), causing the formation of the (Gérard et al. 2008;Gigou 2011). Beyond the pres- lagoon and the barrier reef. The lagoon area is four sures of natural origin, coral reefs (particularly, times the land surface (Thomassin et al. 1989;Mirault fringing reefs) are affected by demographic pres- and David 2009). The relief is the result of an intense sures, such as the deterioration of coastal water past volcanic activity. Sixty-three per cent of the sur- quality, hyper-sedimentation, trampling upon reefs face of Grande-Terre is characterised by slopes greater (shore fishing) and destructive fishing techniques. Thehealthstatusofcoral reefs(Wickel and than 15% and/or located at more than 300 m altitude. Mangroves spread over a linear strip of 76 km and Thomassin 2005;PARETO 2013)ofMayotte an area of 8.5 km , covering 30% of Mayotte coast (Figures 2 and 3) is generally coted as degraded, but some areas show high coral cover. (UICN 2013). They are only located in bays and the Urban development and expansion of human few flat areas of the coastal zone. The nomenclature of mangrove of Mayotte comes in four ecological activities along the coastline are the main factors of degradation of mangroves, including the accumula- assemblages, from land to the sea: salty marshes tion of macro waste and wastewater discharge of all (6%), rear mangroves (22%), central and internal foreshore mangroves (55%) and the pioneer fronts watersheds (Herteman 2010; Thongo 2016). According to the assessment criteria of the Red List of Sonneratia alba (17%). Eleven seagrass species have been found in of French ecosystems (UICN 2015), the salt marshes Mayotte. Generally multi-specific, 56% of seagrass (50 ha) and the rear mangrove (190 ha) are the most threatened habitats, ranked ‘Critically Endangered’ beds are located near the barrier reef on the eastern part of Mayotte, 39% close to the fringing reefs of (CR). The central and internal foreshore mangroves Grande-Terre and 5% around Mtsamboro and (465 ha) are classified as ‘Least Concerned’ (LC). The pioneer fronts of Sonneratia alba (141 ha) are listed Karoni islets (Loricourt 2005). They thrive on sandy substrates outside reef flats areas but the depth of the ‘Vulnerable’. Jeanson (2009) evaluates the regression lagoon (30 to 45 m) does not offer optimal light of mangrove surfaces by 5.5% between 1950 and 2003 conditions for the development of the Indian Ocean (Figure 4). seagrass species. Finally, the seagrass ecosystems, poorly studied in Mayotte, with the exception of specific feeding grounds for the green turtle populations, Chelonia mydas Health status of coral reef and associated (Ballorain et al. 2010), show signs of deterioration that ecosystems cannot yet be specified. The deterioration of water qual- ity, hyper-sedimentation and trampling, are, in this The health status of coral reef varies according to respect, the main threats from human activities. The geographical sectors related to the 1998 and 2010 crossover study between the distribution of seagrass bleaching events (Nicet et al. 2012;Erikssonetal. beds and the quality of water bodies highlighted that 2013). Beside, the crown-of-thorn starfish 7.6 haand296.4hectaresofseagrassbedsare subjected (Acanthaster planci) that feed on corals destroy Figure 2. Health status of the barrier reef (% of coral cover) by station and sector – Modified from PARETO (2013, p. 26). Copyright 2017 by PARETO. Adapted with permission. INTERNATIONAL JOURNAL OF BIODIVERSITY SCIENCE, ECOSYSTEM SERVICES & MANAGEMENT 25 Figure 3. Health status of the fringing reefs of Mayotte – Modified from Wickel and Thomassin (2005, p. 12). Copyright 2017 by Wickel J. and Thomassin BA. Adapted with permission. to water bodies of, respectively, poor and moderate attenuation rate ranges between 92.7 and 97%. quality (between Mamoudzou and Bandrélé), and Finally for the fringing reef, the average width is 456haare locatedinawater bodypresenting ‘good’ 425 m, and the coastal protection function is fulfilled ecological environmental conditions, as is the case of the at 93.4% to 97.4% depending on the coral cover lagoon and offshore water masses (Figure 5). (Table 4). Surface data and health status from each ecosys- The biomass production service is not weighed in tem is synthesised in Table 3. the case of coral reefs as the fish biomass assessment is based on actual fish assemblage data in the current state of the ecosystem. This is a direct measurement. Production functions and weighting factors Mangroves The level of ecosystem services varies according to the Weighting factors for mangroves follow the vulner- health status and/or the vulnerability of ecosystems. ability criteria from UICN (2015). Each vulnerability class is assigned a weight that is used in the moneti- Coral reefs sation of the coastal protection, water purification The weighting calculations for coral reefs are com- and carbon sequestration services (Table 5). The plex. Indeed, as long as the physical structure of the fish biomass is a direct estimate from aerial visual reef remains, coastal protection function is poorly census (Guezel et al. 2009) and Djarifa fishing statis- affected by the health status of the ecosystem and tics in Mayotte (Jamon et al. 2010). weighting factors are never below 90%, despite low coral cover. The average outer barrier reef width is 1150 m, what influences also coastal protection. Seagrass Efficiency varies between 95.5 and 98.5% depending The weighting factors for seagrass beds are based on on the coral cover. For the inner barrier, the average the ecological state of the water bodies presented in width of the reef is 360 m and wave energy Figure 5. For instance, a seagrass patch located within 26 E. TRÉGAROT ET AL. Figure 4. Evolution of mangrove surfaces (ha) over the 1950–2003 period. The seaward arrows illustrate growth of mangroves; the landward arrows represent a regression of mangroves areas – Modified from Jeanson (2009, p. 146). Copyright 2017 by M. Jeanson. Adapted with permission. a water body of moderate quality will be assigned a Seagrass beds reduce waves’ energy by 40% weighting factor of 0.6 (Table 5), used in the mon- (Fonseca and Cahalan 1992; Christianen et al. 2013). etisation of production functions. Using the same value transfer mode than the one used for reefs, the annual value of coastal protection reaches € 63907/km according to the weight factors described in Table 5. Monetary value of ecosystem services Spurgeon et al. (2004) and Cooper et al. (2009) put Coastal protection service forward replacement values of mangroves by respec- The cost of installation of a breakwater system is tive artificial structures of € 254,559/km /year in approximately € 4000/m (France 2014 – GDP/cap.: Samoa (GDP/hab: € 2126) and € 239,204/km /year € 25846) with an annual maintenance cost equivalent in Belize (GDP/hab: € 4219). Considering an average to 4% of the installation cost (Balouin et al. 2012). value of € 88.2 per GDP unit, the value of coastal Taking into account the import taxes of 30% and the protection service of mangroves in Mayotte reaches amortization over 10 years of the structure, the annually € 491,077/km , taking into account the GDP annual cost is € 728/m or € 728,000/km. The transfer per capita during the transfer of value and health of value based on the GDP per capita (€ 7900 in status of mangroves (Table 5, supra). 2014) and taking into account of the weighting fac- The ‘optional’ values of coastal protection provided tors (Table 5) results in an annual cost of € 222,518/ by mangroves and seagrass reach, respectively, € 4.2 km. Overall, monetary values of coastal protection by million/year and € 2.7 million/year. Reported to the coral reefs reach about € 45.1 million/year for the km of each ecosystem, fringing reef has the highest outer barrier, € 3.8 million/year and € 40.9 million/ value (869 K€/year), while barrier reef and inner bar- year, respectively, for inner and fringing reefs where rier reef have respective values of 169 K€/year and these values are considered optional (Table 6). 127 K€/year. Finally, mangroves and seagrass have INTERNATIONAL JOURNAL OF BIODIVERSITY SCIENCE, ECOSYSTEM SERVICES & MANAGEMENT 27 Figure 5. Distribution of seagrass areas in Mayotte and environmental status of coastal water bodies – Modified from Loricourt (2005, p. 43), and PARETO, ASCONIT (2013, p. 143). Copyright 2017 by Loricourt A., PARETO and ASCONIT. Adapted with permission. Table 3. Summary of surface data and health status of coastal ecosystems in Mayotte (Indian Ocean). Coral reef Coral cover % 0–56–10 21–50 51–80 >80 Area (km)96 84 51 47 21 Mangroves Vulnerability CR EN VU NT LC Area (km ) 2.40 - 1.41 - 4.65 Seagrass Ecological state Bad Poor Moderate Good High Area (km ) - 0.076 2.96 4.56 - Table 4. Weighting of coastal protection service associated to coral reefs of Mayotte (Indian Ocean). Type of reef Outer barrier Inner barrier Fringing reef Reef flat width (m) 1150 360 425 Coral cover (%) Linear (km) Weighting factors (%) Linear (km) Weighting factors (%) Linear (km) Weighting factors (%) 0–5 45 95.5 0.8 92.7 71.2 93.4 6–20 36 96.0 4.2 93.3 70.6 94.0 21–50 22 96.8 3.1 94.4 41.9 95.1 51–80 27 97.8 3.1 95.9 11.1 96.4 >80 11 98.5 6.8 97.0 0.2 97.4 Coral cover on the barrier and the reef flat are considered equal. 28 E. TRÉGAROT ET AL. Table 5. Weighting of ecosystem services of mangroves and seagrass of Mayotte (Indian Ocean). Mangroves Seagrass Ecosystem Vulnerability Area (ha) Ecological state Area (ha) Weighting factors (%) Health status CR 240 Bad – 20 EN - Poor 7.6 40 VU 141 Moderate 296.4 60 NT - Good 456 80 LC 465 High – 100 CR: Critically endangered; EN: Endangered; VU: Vulnerable; NT: Near Threatened; LC: Least Concerned (UICN 2015). Ecological state according to water masses quality (PARETO, ASCONIT 2013). values per km of 491 K€/year and 353 K€/year, data on the water purification by algae, it is difficult respectively. to quantify the weighted value. It is likely that the real value of water purification by coral reefs with nearly 60% algal cover is substantially higher. Water purification service Mangroves water purification represents up to € Coral reef organisms have limited ‘water purification’ 1.6 million/year, with a value per unit area of 191 K capabilities, evaluated by De Groot et al. (2012)toUS 2 2 €/km /year, well below that of seagrass beds which is $ 8500/km /year, or € 7752/km /year (Table 6). € 1.2 million/km /year. The monetary value of the As reported by Lal (2003), the value of treatment of water purification service provided by seagrass beds inland waters by mangroves in Fiji represents € 2 in Mayotte reaches almost € 9.5 million/year. 174,200/km /year for a GDP/capita of € 5078 in 2003. According to the transfer of values for Carbon sequestration Mayotte, and the health status of mangroves, the Considering the stock market value of a tonne of CO value of water treatment by mangroves reaches equal to € 6.12 (2015) and the values of net produc- annually € 191,435/km . tivity of mangroves (3667 tCO eq/km /year) and sea- According to Costanza et al. (1997), the value of the grass (435 tCO eq/km /year), monetary values of water purification service produced by seagrass beds is carbon sequestration for these two ecosystems are, US$ 19002/ha/year or € 1,732,255/km /year (Table 6). respectively, 134 K€/year and 15 K€/year. The value This result is to be interpreted with caution because it of carbon sequestration per km for mangroves is 8.3 is the only existing value from the literature without times that of seagrasses (€ 15853 against € 1911). This clarification on the monetary valuation of this service difference is explained by the size of the plants struc- (Barbier et al. 2011). If we consider the weighting turing each ecosystem. factors (Table 5), the value of water purification for seagrass beds is € 1,243,759/km /year. The values of water purification services vary Fish biomass production greatly according to ecosystems. Coral reefs have a The average biomass of commercial fish species of total value of € 2.7 million/year, but in the absence of Mayotte coral reefs is estimated at 95.8 g/m (Wickel Table 6. Monetary values of ecosystem services provided by CRAE of Mayotte (Indian Ocean). Length Area 2 2 Ecosystem services (km) (km ) Max Unit value Monetary value (€/year) Value per km (€/year) Coastal Protection Outer barrier reef 210 266 222,518 €/km 45,089,035 169,508 Optional values Inner barrier 18 30 222,518 €/km 3,816,249 127,208 Fringing reefs 195 47 222,518 €/km 40,861,390 869,391 Mangroves - 8.46 695,200 €/km 4,154,515 491,077 Seagrass 42 7.6 89,007 €/km 2,684,095 353,170 Water treatment Coral reefs 342 7752 €/km /year > 2,651,184 > 7752 Mangroves 8.46 271,008 €/km /year 1,619,544 191,435 Seagrass 7.6 1,732,255 €/km /year 9,452,569 1,243,759 Carbon sequestration Coral reefs 342 - - - Mangroves 8.46 22,442 €/km /year 134,113 15,853 Seagrass 7.6 2662 €/km /year 14,527 1911 Fish Biomass Production Coral reefs 342 120 t/km /year 92,340,000 270,000 Mangroves 1.41 25 t/year 75,000 53,191 Seagrass 7.6 1 t/km /year 16,370 2154 Value of a tonne of CO in the stock market: 6.12 € (September 2015). The value added per kilo of fish is € 3 (Own survey 2015). INTERNATIONAL JOURNAL OF BIODIVERSITY SCIENCE, ECOSYSTEM SERVICES & MANAGEMENT 29 et al. 2005) and 82.8 g/m for the stations of the Coral statuses. The total VUI would be € 188 million if Reefs Observatory (Chabanet 2002). The average ecosystems were in pristine conditions, which repre- 2 2 value is either 90 g/m sents € 37 million more. Considering the optional or 90 t/km for all the reefs of Mayotte. coastal protection values, the total economic value The evaluation of fish biomass in mangroves is would be € 245 million for ecosystems in very good based on traditional fishery: djarifa fishing, exclu- condition, that is, € 42 million more than the current sively women practice. The fishing gear, the ‘lamba’, value of € 203 million. is similar to a beach senne with a much smaller mesh. The fishing practice gathers a team of three to nine women for one to three djarifas. They target small Discussion pelagic and juvenile fish out of mangroves, within protected bays and on the reef flat at low tide The deterioration of ecosystem health status changes (Jamon et al. 2010). The average number of djarifa the amount of services produced. However, services are not affected in the same way, as a specific func- fishing trips in Mayotte was estimated at 1092 per year in 2009, of which 70% in mangroves (Guezel tion can increase in degraded ecosystems. This para- et al. 2009) or 764 djarifa fishing/year. According to dox is especially true for water purification and carbon sequestration services provided by coral Jamon et al. (2010), the average weight of the catches of one fishing trip in mangroves is 32.8 ± 10.4 kg, or reefs. When coral reefs are degrading along with an annual total of approximately 25 ± 8 t/year algal overgrowth, the production functions increase due to the macroalgae capacities for water purifica- (Table 6). (Gullström et al. 2002) found that the exploited tion and carbon absorption. However, the coastal biomass of seagrass fish in Mozambique is protection and biomass production functions are, respectively, hardly and moderately impacted by approximately 1 t/km /year. When transposed to coral coverage as long as the physical structure of Mayotte and by applying weighting factors the reef remains. Indeed, coral reef organisms have (Table 5), the exploitable biomass accounts 0.72 t/km /year. limited or negligible ‘water purification’ abilities com- pared to seagrass beds (Costanza et al. 1997;De The total biomass production value for coral Groot et al. 2012). However, algae overgrowth, reefs reaches 92 M€/year, much higher than the values for mangroves and seagrass beds, respec- usually leads to the reduction of live coral cover (Hughes 1994; McManus et al. 2000; Mumby 2009), tively, 75 K€/year and 16 K€/year. but contributes positively to water purification by The value per unit area (km ) helps to show the absorbing part of the nutrients (Lapointe 1997). real marketable fishery potential of each ecosystem, Considering the steep growth of macroalgae induced reefs having the highest value (270 K€/year) com- by the enrichment of coastal waters with nutrients pared to mangroves (53 K€/year) and seagrass beds and their ability to absorb excess nitrates and phos- (2 K€/year). phates, the water purification service provided by The economic value of indirect uses is estimated at degraded reef ecosystems will increase. A high eco- € 151 million/year, of which € 140 million originates from coral reefs only, € 1.8 million from mangroves nomic value, not quantifiable in the present state of and € 9.5 million for seagrass (Table 7). knowledge, is then allocated to a service provided by a degraded state of the original ecosystem. This pro- Coastal protection and biomass production are the two major ecological services, followed by the sea- duction function would be minimal in a healthy reef grass water purification capacity. Optional values ecosystem. It exists thereupon only because of the degradation of the ecosystem under pressures of associated with coastal protection from inner and fringing reefs, mangroves and seagrass add € 52 mil- anthropic origins. Carbon absorption by algae lion. By reporting the IUV per km through photosynthesis is unequivocally proven and of ecosystem, even comparable to that of seagrasses (Beer and Koch seagrass rank first with the highest value (€ 1.2 mil- 1996; Hanelt et al. 2003) while it is questioned on lion/km /year), followed by coral reefs (€ 0.4 million/ 2 2 healthy reef formations (Shaw et al. 2015). Eutrophic km /year) and mangroves (€ 0.2 million/km /year). These values reflect ecosystems in various health conditions in coastal waters of Mayotte promote algal Table 7. Overview of maximum IUVs and monetary IUVs gathered for the CRAE or Mayotte (Indian Ocean). CR M S Total Options Total + options IUV max 172.5 M€ 2.6 M€ 13.2 M€ 188.3 M€ 57.0 M€ 245.3 M€ IUV calculated 140.1 M€ 1.8 M€ 9.5 M€ 151.4 M€ 51.5 M€ 202.9 M€ % 81% 71% 72% 80% 90% 83% Total loss 32.4 M€ 0.7 M€ 3.7 M€ 36.9 M€ 5.5 M€ 42.4 M€ IUV/km 0.4 M€ 0.2 M€ 1.2 M€ 0.4 M€ 0.6 M€ 0.6 M€ 30 E. TRÉGAROT ET AL. total loss of coral cover leads to a reduction of 39% growth; the function of carbon sequestration of reef fishery landings in Eastern Indonesia. increases accordingly, as does the monetary value of this service. McClanahan et al. (2016) found that natural fish biomass in pristine coral reefs in the Western Pascal et al. (2014) evaluated the carbon sequestra- Indian Ocean can reach 120 t/km tion service for Mayotte at € 2,380,000. In this article, . Using this later the evaluation is based solely on the absorption of value, the maximum monetary value of fish biomass carbon dioxide, not taking into account the amount production in Mayotte reaches € 123 million, that is, of carbon that has been stored for hundreds of years € 31 million more than the monetary value of € 92 in the soil. Consequently, the value in this paper is 16 million obtained. Pascal et al. (2014) evaluated the times lower than the previous stated value: € 148,640. commercial biomass production service for both Valuation of carbon sequestration service varies commercial and self-consumption fisheries related greatly in the literature. The reason is the number to CRAE such as coastal fisheries, deep-sea fishing of compartments to valued (soil and/or living bio- and supervised sport fishing and reached an annual mass) and the number of processes (carbon storage value of € 9,180,500. Our results refer to the fish and/or carbon absorption) included in the evaluation. biomass production (of which a portion forms also Also, one of the major factors is to determine the a provisioning service as part of the biomass sub- value of one ton of carbon dioxide. According to jected to fishing) and represent the ecosystem ability Canu et al. (2015), the value of one ton of CO to produce exploitable fish biomass worth is € 92,340,000 per year, which significantly differs € 19, which appears to be very conservative compared to the value of € 97/tCO reported by Van Den Bergh from the previous cited report value. Mangroves and seagrass beds of Mayotte actively and Botzen (2014). In this article, the current market contribute to the purification of coastal waters and nutri- price is the reference (€ 6.12 in 2015). Degradation of coral substrate and erosion of reefs ent absorption. This ecosystem service generates the highest monetary value (respectively, € 1.6 million and are rather slow mechanisms: the changes occurring in ecosystems neither affect entirely the coastal protec- € 9.5 million, representing 89 and 99% of the total value tion service (Sheppard et al. 2005), nor the biomass of indirect use services provided by these ecosystems). However, even if these ecosystems absorb excess nutri- production (Ainsworth and Mumby 2015). Other parameters influence the production of the service ents, the fact remains that poor water quality negatively such as the presence of a barrier reef and the extent impacts their functioning. According to Herteman (2010), the wastewater effect on mangrove crabs popula- of the reef flat (Ferrario et al. 2014). Degraded coral reef communities hardly affect wave energy attenua- tion in Mayotte translates into a modification of the tion, reducing it by 10% maximum (Sheppard et al. nitrification/denitrification process (bioturbation) and over time significantly perturbates the mangrove ecosys- 2005). The weighting by the health status is therefore not significant; the associated value remains high tem. For seagrass beds, excess nutrients favours algae accordingly. Services of coastal protection and carbon growth at the cost of seagrass plants (Duarte 2002). Besides the need to maintain production func- sequestration are discussed in Pascal et al. (2014). Although very interesting, they used a detailed tionsby implementingspecificmeasurestomiti- experimental approach based on the evaluation of gate or even annihilate the effects of human avoided cost. As a result, coral reefs that would pro- activities, coastal ecosystem preservation also tect highly urbanized areas are worth much more requires conservation of iconic species, some of than coral reef protecting pristine coastal habitats which are listed on the red list of UICN. Seagrass without any human infrastructures. In other words, beds are important feeding areas for dugongs if there is no infrastructure to protect, coral reef is (Dugong dugong – Vulnerable), less than 10 indivi- worth nothing in terms of coastal protection, which is duals remain in the lagoon of Mayotte (Pusineri a very limiting approach. As a result, Pascal et al. et al. 2013), green turtles (Chelonia mydas – (2014) evaluated the coastal protection in Mayotte at Endangered) and, to a lesser extent, hawksbills tur- € 10.5 million while in our article the value reaches € tles (Eretmochelys imbricata – Critically 45.1 million. Endangered). In this context, the preservation of The progressive and rapid shifts between coral dense and healthy seagrass beds is a key issue, dominant communities and dense algal populations associated to strong regulations to limit poaching affect the structure of fish communities in coral reefs and risks of collision with boats. The decline of (Wilson et al. 2006), but not necessarily the biomass. seagrass beds has much more serious and durable The complex three-dimensional structure of the reef consequences than the sole disappearance of this is determining for the presence of dense fish popula- ecosystem (Waycott et al. 2009), given the close tions. The proportion of herbivorous fish is increas- relationship with associated ecosystems. ing in algae dominated environments. According to The marine and coastal environments of Mayotte Ainsworth and Mumby (2015), it appears that the have been deteriorating for several decades. Between INTERNATIONAL JOURNAL OF BIODIVERSITY SCIENCE, ECOSYSTEM SERVICES & MANAGEMENT 31 species richness. Therefore, nutrient loading is a key 1989 and 2004 (15 years), the coral cover of fringing parameter to control, prior to protect coastal marine reefs has decreased by 60% (Wickel and Thomassin 2005), while between 2005 and 2013 (8 years) that of ecosystems. Protection of CRAE is a major challenge for the barrier reef has shrunk by 15% (PARETO 2013). island of Mayotte in the current context of uncon- Degradation also occurs in mangroves where Sonneratia pioneer fronts have diminished by 43 ha trolled urbanisation of the coast (PADD 2008). in 30 years (Jeanson 2009). Such changes affect the production functions of ecosystems. For pristine coastal environments, the maximum value of these Conclusion services would reach € 188 million/year (up to € 245 million with optional values of coastal protection). The total value of indirect uses provided by CRAE of Given the actual state of degradation of ecosystems, Mayotte reaches € 176 million/year. This amount is the IUV calculated (€ 151 millions) is € 37 million significant to the local economy of Mayotte since it is lower than the optimal value. If we consider the higher than the added value generated by the agricul- optional values, the IUV calculated reaches € 203 ture: 95 M€, the industrial: 57 M€ or the construction million (€ 42 million lower than the optimal value). sector: 135 M€ (INSEE 1975–2017). The estimated The gradual degradation of ecosystem health in values of coastal protection (€ 30 million) and biomass recent years is the principal reason. Natural events production (€ 81 million) by coral reefs and those of such as increased water temperature leading to coral water purification services provided by mangroves (€ bleaching, hurricanes and proliferation of crown-of- 1.6 million) and seagrass beds (€ 9.5 million) emphasise thorn starfish Acanthaster had major contribution to the economic interest in conservation efforts for the the changes observed. However another factor, much preservation and restoration of ecosystems. Coral reefs more significant, is imputable to public inaction, that contribute to 91% of the economic value derived from is, the lack of political consideration, laissez-faire the four ecosystem services presented in this article. attitudes and the deficient interest in understanding However, the ecosystem with the highest monetary the ecological and economic functions of value, relative to one square kilometre, is seagrass marine coastal environments. Thus, overall the lack- beds (€ 1.2 million), followed by reefs (€ 0.4 million) ing € 37 million/year in services may be interpreted and mangroves (€ 0.2 million). as the cost of public non-intervention in Mayotte Human activities contribute to the degradation of CRAE management. Mayotte CRAE including remote reefs, located more The results of the Mayotte study have been pre- than 10 km away from the coast. One third of these sented to the Environment, Planning and Housing reefs have a coral cover between 0 and 20%. This Directorate. The economic development of Mayotte assessment is worrying in a context of economic is a priority, which relegates environmental impera- development and increasing risks of degradation. tives in the background. The same observation can be Consequently, the economic loss from indirect use made currently to all French Overseas Collectivities values reaches € 32 million. where IFRECOR works. The lack of understanding This study highlights the close link between environ- and additional mechanisms to integrate economic mental conservation and economic valuation challenges, evaluations in the decision-making process makes and should provide support for future policy decisions unlikely the use of the results of such work, and on coastal management and marine environmental pro- constitutes a very critical issue for the marine park tection. The paradox highlighted that a higher monetary of Mayotte. value is assigned to a deteriorating ecosystem, however, It is expected that the IUV will continue to shows the limits of the economic evaluation. It is there- decrease in the near future because too little is done fore necessary to accompany the results with interpreta- to counter pollution by sewage releases. In 2015, only tion elements, essential to public decisions. the Mamoudzou municipality was equipped with a Several lines of study can be sketched in this functional water treatment plant which can process regard. This involves, for example, quantifying the discharges of 10000 inhabitants, while the total popu- water purification function by seagrass beds, but lation of the island exceeds 235,132 inhabitants. The also by algae that are becoming particularly impor- shortage of water treatment therefore degrades the tant among reef communities. In order to monetise coastal water quality, meaning the presence of heavy this service, it is necessary to estimate (1) the absorp- metals, polyaromatic hydrocarbons and polychloro- tion rate of nutrients by an ecosystem or organism biphenyls (Thomassin et al. 2010). According to and (2) the replacement cost of a technological arte- Duprey et al. (2016), eutrophication of coastal waters fact (water treatment plant) for an equivalent water causes a decrease in coral cover and a decrease in treatment level. 32 E. TRÉGAROT ET AL. Bridge TC, Hughes TP, Guinotte JM, Bongaerts P. 2013. Acknowledgements Call to protect all coral reefs. Nat Clim Change. 3:528– This study was conducted under the theme of transversal interest ‘Total economic value of coral reefs and associated Burke L, Reytar K, Spalding M, Perry A. 2011. Reefs at risk ecosystems of the French overseas territories’ of IFRECOR . revisited. Washington (DC): World Resources Institute. The authors thank the DEAL Mayotte, the General Council Cabral P, Levrel H, Schoenn J, Thiebaut E, Le Mao P, of Mayotte, the University of Mayotte, and the Marine Park Mongruel R, Rollet C, Dedieu K, Carrier S, Morisseau of Mayotte for providing all completed studies of these F. 2015. Marine habitats ecosystem service potential: a ecosystems, their health status and the pressures, and vulnerability approach in the Normand-Breton (Saint developed the economic and environmental issues in Malo) Gulf, France. Ecosyst Serv. 16:306–318. Mayotte. Finally, the authors would like to thank Claire Canu DM, Ghermandi A, Nunes PA, Lazzari P, Cossarini Montocchio and Christopher Martin for their help in G, Solidoro C. 2015. Estimating the value of carbon proofreading and translating this paper. sequestration ecosystem services in the Mediterranean Sea: an ecological economics approach. Global Environ Chang. 32:87–95. Chabanet P. 2002. Coral reef fish communities of Mayotte Disclosure statement (western Indian Ocean) two years after the impact of the 1998 bleaching event. Mar Freshwater Res. 53:107–114. No potential conflict of interest was reported by the Christianen MJ, van Belzen J, Herman PM, van Katwijk authors. MM, Lamers LP, van Leent PJ, Bouma TJ. 2013. 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Coral mortality increases wave energy reaching Centre, Townsville, Australia ed. shores protected by reef flats: examples from the Wilson SK, Graham NA, Pratchett MS, Jones GP, Polunin Seychelles. Estuar Coast Shelf S. 64:223–234. NV. 2006. Multiple disturbances and the global degrada- Spurgeon J, Roxburgh T, O’ Gorman S, Lindley R, Ramsey tion of coral reefs: are reef fishes at risk or resilient? Glob D, Polunin N. 2004. Economic valuation of coral reefs Change Biol. 12:2220–2234. http://www.deepdyve.com/assets/images/DeepDyve-Logo-lg.png International Journal of Biodiversity Science, Ecosystem Services & Management Taylor & Francis

Evaluation of coastal and marine ecosystem services of Mayotte: Indirect use values of coral reefs and associated ecosystems

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© 2017 The Author(s). Published by Informa UK Limited, trading as Taylor & Francis Group.
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10.1080/21513732.2017.1407361
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Abstract

INTERNATIONAL JOURNAL OF BIODIVERSITY SCIENCE, ECOSYSTEM SERVICES & MANAGEMENT, 2017 VOL. 13, NO. 3, 19–34 https://doi.org/10.1080/21513732.2017.1407361 SPECIAL ISSUE: OPERATIONALISING MARINE AND COASTAL ECOSYSTEM SERVICES Evaluation of coastal and marine ecosystem services of Mayotte: Indirect use values of coral reefs and associated ecosystems a,b a c Ewan Trégarot , Pierre Failler and Jean-Philippe Maréchal a b Portsmouth Business School, University of Portsmouth, Portsmouth, UK; Observatoire du Milieu Marin Martiniquais, Schoelcher, Martinique, France; Nova Blue Environment, Schoelcher, Martinique, France ABSTRACT ARTICLE HISTORY 2 2 2 Received 30 September 2016 Coral reefs of Mayotte (342 km ), seagrass beds (7.6 km ) and mangroves (8.5 km ) provide Accepted 14 November 2017 important ecosystem services of which the most important are the coastal protection, fish biomass production, carbon sequestration and water purification. The quantity and quality of EDITED BY these services have been decreasing steadily for several years and should continue to do so if Sebastian Villasante no action is taken to contain anthropogenic pressures. The coral cover of the fringing reefs KEYWORDS and the barrier reef has thus declined, respectively, by 60% in 15 years and 15% in 8 years. Indirect use values; The pioneer front of Sonneratia for mangroves has declined by 13% in 6 years, and for ecosystem services; coral seagrass beds, the water quality suggests a degraded state. The estimated annual value of reefs; mangroves; seagrass these services amounts to EUR 124 million. It would be EUR 162 million if the ecosystems beds; Mayotte; Indian Ocean were in pristine conditions. The article shows that the preservation of coastal ecosystems is essential from an economic point of view. Introduction Fieldwork was carried out in 2014 and 2015 in Coral reefs are among the most productive marine eco- Mayotte. The territory acquired the status of French systems, especially in terms of biodiversity (Wilkinson overseas department and region in 2011. The last census 2008). On a global scale, a fifth has been destroyed and counted 235,132 inhabitants (INSEE 1975–2017)for an half of the remaining reefs are endangered (Wilkinson area of 376 km , making Mayotte the overseas depart- 2008;Burke et al. 2011;Bridgeetal. 2013;Hoegh- ment with the highest population density (625 people Guldberg 2014). Beyond their ecological importance per km ). (habitats, spawning areas, etc.) and coastal protection The aim of the article is to present the monetary dimension, coral reefs and associated ecosystems (sea- value of IUV relative to the ecological services pro- grass beds, mangroves and mudflats) have important vided by CRAE of Mayotte. These services such as economic and social scopes in the French overseas terri- coastal protection, production of fish biomass, water tories, particularly for fishing, tourism and recreation. purification and carbon sequestration are not sub- Since 2006, the French Government has implemen- jected to market exchanges. ted a programme to evaluate the total economic value Schröter et al. (2005) stated: ‘an increase in the (TEV) of coral reefs and associated ecosystems (CRAE) habitats vulnerability is likely to decrease the supply of all French overseas territories, through the French of ecosystems’. The assessment of marine habitats Coral Reef Initiative (IFRECOR). A methodology was vulnerability has become important to point out developed and approved by the ministry of the envir- anthropogenic threats (Halpern et al. 2007) and eval- onment. These guidelines have been included in the uate marine habitats ecosystem services potential terms of reference for the Mayotte assessment. based on vulnerability approaches (Bouahim et al. Assessment is done following the methodology detailed 2015, Cabral et al. 2015). The article relates an aspect in the guidelines produced by Maréchal et al. (2014)asa rarely considered in the evaluation of coastal ecosys- part of IFRECOR. The TEV expressed in euro/year, tem services, namely the integration of ecosystem sums up the use values (UV), the indirect use values health status in the weighting of production func- (IUV) and the non-use values (NUV). Use values are tions. A healthy ecosystem provides a full range of related to leisure activities such as bathing and diving or services, the capacity of which decreases as and when commercial uses such as commercial fishing. Indirect it is disturbed, polluted, weakened, etc. In other use values concern regulating ecological functions. words, a healthy ecosystem produces ecological ser- Non-use values refer to the spiritual dimension and vices that are quantitatively and qualitatively higher existence of the nature (Corvalan et al. 2005). than the same ecosystem in poor condition. The CONTACT Ewan Trégarot ewan.tregarot@gmail.com © 2017 The Author(s). Published by Informa UK Limited, trading as Taylor & Francis Group. This is an Open Access article distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/4.0/), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited. 20 E. TRÉGAROT ET AL. Marine science institute of Martinique (Observatoire services: coastal protection against erosion, coastal water purification, atmospheric carbon sequestration and fish du Milieu Marin Martiniquais – OMMM) has devel- oped, as part of the ecological monitoring of the biomass production (of which a portion also forms a coastline (Legrand et al. 2008), a method calibrating provisioning service for fisheries). It is considered that for coastal protection (given the health status of coastal marine ecosystems for Martinique, which is applied here. The article casts the juxtaposition of natural barrier reefs in Mayotte): additional light on how to take into account this key The outer barrier reef (208 km – Thomassin environmental variable in assessing coastal ecological et al. 1989) ensures global coastal protection, services. The inner reefs (inner barrier and fringing reef), The article is structured in four parts. In the first seagrass beds and mangroves have ‘optional’ part materials and methods for the valuation of eco- coastal protection value most of the time, but system services of coastal protection, carbon seques- are not negligible in case of exceptional weather tration, water purification and biomass production events. are presented. In the second part, the results show Carbon sequestration is not taken into account for the health status of Mayotte coastal ecosystems then, coral reefs because of lack of data. Indeed, coral calcifi- selected production functions are described before cation as a carbon storage process is tangible because addressing the weighting factors to refine the level one must consider organisms’ respiration and coral of services provided. From these elements, a mone- dissolution for which CO is thus recirculated into the tary valuation of IUV is proposed taking into account atmosphere (Shaw et al. 2015). Table 1 summarises the the weighting factors of ecosystem health status. In production functions selected for the CRAE of Mayotte. the third part, a discussion is offered on the most important aspects to remember, especially those that contribute to the development of public policy. A conclusion summarises the determining elements. Ecosystem mapping and health status assessment Wickel and Thomassin’s(2005) fringing coral reefs map and PARETO’s(2013) barrier reefs map allow Materials and methods estimation of the ecosystem surfaces (mandatory for The valuation of ecosystem services was conducted in valuation of water purification and biomass produc- Mayotte using the method developed by Maréchal tion services) and the linear length of each ecosystem et al. (2014) under the IFRECOR framework on along the coastline (mandatory for calculation of the ‘Socio-economic valuation’. It follows five stages: (1) coastal protection service). The health status of coral identification of ecological ecosystem services linked reef was assessed based on alive coral cover percen- to indirect uses, (2) ecosystem mapping and health tage compared to the total reef areas. Mangroves fine status assessment, (3) definition of production func- mapping study from Jeanson (2009) was used to tions and assessment of produced services, (4) appli- characterise salt marshes, rear mangrove, central cation of a weighting coefficient and (5) and inner foreshore mangroves and pioneer fronts determination of indirect use (monetary) values. of Sonneratia alba, a species of mangrove. The health status of mangroves was assessed according to their vulnerability classification, established under the eva- Identification of ecological ecosystem services luation criteria of the Red List of French ecosystems The identification of ecological services linked to indir- (UICN 2015). Discussions with members of the ect uses follows the Millennium Ecosystem Assessment National Forestry Commission and the UICN during classification (Corvalan et al. 2005). A review of Mayotte the meeting to validate the vulnerability criteria marine and coastal biodiversity literature was conducted allowed clarification on the methodology. The to collect information on coastal habitat maps prior to Department of Agriculture and Forestry (2006) pro- fieldwork (Wickel and Thomassin 2005; Jeanson 2009; duced a map for seagrass beds. No data on seagrass Herteman 2010; Jamon et al. 2010;PARETO 2013). The health status was available at the time of this study. ecosystem services selected for Mayotte are regulation We estimated seagrass beds status using Mayotte Table 1. Selected ecosystem services for marine coastal ecosystems of Mayotte (Indian Ocean). Coral reefs Services Outer barrier Inner barrier Fringing reef Mangroves Seagrass Coastal protection ✔ Option Option Option Option Water treatment ✔✔ ✔ Carbon sequestration NA ✔✔ Biomass production ✔✔ ✔ NA: non-applicable production function; Option: indicates an optional production function. INTERNATIONAL JOURNAL OF BIODIVERSITY SCIENCE, ECOSYSTEM SERVICES & MANAGEMENT 21 water bodies assessment under the EU Water respectively, to 14 and 15% of the carbon storage Framework Directive (PARETO, ASCONIT 2013). capacity of the oceans (Laffoley and Grimsditch 2009; Waycott et al. 2009; Donato et al. 2011). The respective net productivities of Sonneratia/ Definition of production functions and Avicennia and Rhizophora mangrove communities assessment of produced services are 9.54 tC/ha/year and 10.5 tC/ha/year Ecosystem services estimation relies on ecosystems (Poungparn and Komiyama 2013). These values surface data, assessment of their health status and are applied to Mayotte mangroves. The estimated net productivity of seagrass beds is maximum production level for each service (Table 2). While coastal protection, carbon sequestration and 1.19 tC/ha/year (Duarte et al. 2010), equivalent to 435 biomass production services benefit from extended tCO eq/km /year on average. This later value is references, water purification valuation is based only applied to Mayotte case study. on Costanza et al. (1997) monetary reference despite the absence of reference work to validate this result. Water purification Water purification is the absorption capacity of nutri- Coastal protection ents by ecosystems in relation to their surface and The coastal protection service mitigates extreme health status. Coral reefs have very low capacity of weather events such as tsunami or hurricane swells water purification, but the coral – algal shift in coral (Kunkel et al. 2006). The reef structures absorb up to reefs increases the water purification function accord- 90% of the waves energy (Ferrario et al. 2014). If ing the intensification of algae cover. extreme natural conditions threaten the coastline of The capabilities of bio-remediation of mangrove Mayotte, the inner barrier reef, the fringing reef, forests were assessed at Malamani (Herteman 2010) seagrass beds and mangroves would absorb most of and studies are still under progress. This study shows the waves’ energy left. Only two sectors in Mayotte that wastewaters are partly absorbed by the aremoresensibletocyclonicswell giventhe direc- vegetation. tion of waves that may enter the lagoon through reef Seagrass meadows can trap nutriment-loaded sedi- pass: Pointe Kani in the south and Tsingoni bay on ments, acting as coastal water filters (Duarte 2000). the west coast where waves’ height can remain Besides, seagrass plants absorb dissolved minerals greater than 1 m while for the rest of Mayotte and nutrients for their own growth directly from coast, waves’ height is less than 50 cm (Lecacheux water. et al. 2007). Seagrass beds stabilise the sediment and reduce waves’ energy by about 40% (Fonseca and Cahalan 1992; Christianen et al. 2013). The last Biomass production physical barriers, composed of mangrove forests, Coral reefs provide habitat and nursery grounds for dissipate wave energy and significantly diminish many fish species and represent very important fish- wave height over very short distances (Jeanson ing areas for the local population. The pioneer fronts 2009). Mangrove trees Sonneratia sp.characterise of Sonneratia alba communities are submerged by the pioneer front of mangroves and absorb about seawater and house fifty-eight species of fish 50% of wave energy over a distance of 100 m (Mazda (Ponton et al. 2013). Seagrass areas also form nursery et al. 2006). grounds for juvenile fish that use the dense canopy as a shelter during early life stages (Pogoreutz et al. Carbon sequestration 2012). Other larger species use seagrass beds as tran- Mangroves and seagrasses ecosystems form signif- sition area to feed and hunt (Unsworth et al. 2008), icant carbon sinks and each contribute, and are targeted by fisheries. Table 2. Production functions and services estimation. Indirect use service Definition Data used for services estimation Coastal protection Ecosystem’s ability to reduce wave power/energy ● Coastline/surface area of ecosystems playing a protection role ● Coefficient of wave power attenuation provided by ecosystem ● Health status of ecosystems Water treatment Ecosystem’s ability to absorb nutrients ● Area of ecosystem playing a water treatment role ● Health status of ecosystems Carbon storage Ecosystem’s ability to absorb atmospheric or dissolved carbon ● Area of ecosystem ● Average carbon absorption rate of ecosystem ● Health status of ecosystems Biomass production Ecosystem’s ability to produce exploitable fish biomass ● Biomass production rate of ecosystem ● Portion of marketable and exploitable species 22 E. TRÉGAROT ET AL. canopy height and density of plants/trees are often The fish biomass production (of which a por- used (Dirberg 2015; Taureau et al. 2015). tion forms also a provisioning service as part of the biomass is subject to fishing) represents the ecosystem ability to produce exploitable fish Determination of indirect use monetary values biomass. Determining indirect use monetary value is specific to each service and ecosystem. Carbon sequestration and production of fish biomass valuation use, respec- Application of a weighting coefficient tively, the price market of a tonne of CO and kilo- Production functions are weighted according to the gram for fish. Water purification and coastal estimated amount of service provided by the ecosys- protection functions are evaluated according to repla- tem. Health status indexes and levels of vulnerability cement cost and value transfer methods. The value of marine environments are elaborated from pub- transfer method was used to provide economic value lished references. They are applied to a production of ecosystem services through a simple approach function that would provide 100% of the service. usable in different contexts and for comparison. The coastal protection service provided by coral This methodology, although questionable, was reefs is weighted by their health conditions (Wickel retained in the IFRECOR terms of reference for this and Thomassin 2005; PARETO 2013) and the meth- study, essentially because it can be easily adjustable to ods from Sheppard et al. (2005) and Ferrario et al. any case study. Coastal linear length ecosystem and (2014), considering that: gross domestic product (GDP) are basically the only A 100% mortality of live corals in coral reefs data necessary to obtain a gross estimate. This article leads to an average 10% decrease of the waves provides guidance for conducting and refining such attenuation effect; value transfers to facilitate its application despite the The outer barrier absorbs up to 91% of the wave various constraints that make primary data collection power; impractical. A linear model correlates coral reef health status The coastal protection service value is calculated and wave attenuation; using the method of costs replacement by artificial The width of the reef flat influences the attenua- breakwater-like structures such as: tion of the remaining wave power. PC ¼ðÞ C  E  PIB  T =PIB (1) i i i m i r The width of the reef flat is 1150 m for the outer barrier (between 800 and 1500 m) and 425 m for the with: fringing reef (between 50 and 800 m) (Jeanson 2009). PC = value of coastal protection for ecosystem i The average width of the inner barrier reef flat, mea- (€/year), sured from 18 measurements of aerial images (Google C = cost of producing a man-made structure Earth) is 360 m. providing the same service of coastal protection as Ecosystem vulnerability categories established by ecosystem i (€/km/year or €/km /year), the UICN (2015) for mangroves were used to weight E = coastline or surface of ecosystem i (km mangrove services of Mayotte: 20, 40, 60, 80 and or km ), 100%, respectively, for habitat critically endangered PIB = GDP/capita of Mayotte (€), (CR), endangered (EN), vulnerable (VU), near threa- PIB = GDP/capita of reference study area (€) and tened (NT) and of least concern (LC). T = type of protection provided by ecosystem The European Water Framework Directive (WFD) (between 0 and 1 for service provided, respectively, recommendation on seagrass beds classification was between 0 and 100%). used for the weighting of ecosystem services. Five The water treatment value is obtained from the health status categories are used to assess ecosystem estimated replacement cost of coastal waters natural (bad, poor, moderate, good and high) to which will purification functions by technological artefacts be associated the respective weighting coefficients 20, such as: 40, 60, 80 and 100%. TE ¼ðÞ C  E  PIB =PIB (2) i i i m r Weighting of ecosystem services of CRAE by health status is poorly developed in the literature with: and few indicators are available to estimate the health TE = value of water treatment provided by eco- status of coral reefs, mangroves and seagrass beds. system i in Mayotte (€/year), WFD indicators have been created or are under C = water treatment reference value per unit of development (Le Moal and Aish 2013; Dirberg area of ecosystem i (€/km /year), 2015). For coral reefs ecosystems, coral and macro- E = total surface area of ecosystem i providing a algae covers are the major variables (Le Moal and type of water treatment (km ), Aish 2013), while for mangroves and seagrass beds, PIB = GDP/capita of Mayotte (€) and m INTERNATIONAL JOURNAL OF BIODIVERSITY SCIENCE, ECOSYSTEM SERVICES & MANAGEMENT 23 PIB = GDP/capita of reference study area (€). B = average biomass production per unit area for r i The value of carbon sequestration services is ecosystem i, obtained by estimating the amount of carbon assimi- T = portion of marketable and exploitable species lated by the ecosystem multiplied by the average price (between 0 and 1), of a tonne of CO according to the following E = total area of ecosystem i and 2 i equation: VA = average value added per kilo of fish for the considered region. SQ ¼ A  E  PCO (3) i i 2 with: SQ = value of carbon sequestration for ecosystem i Results (€/year), Marine ecosystems mapping A =CO absorption rate for ecosystem i 2 i(tCO /km /year), Coastal ecosystems of Mayotte consist of coral reefs, E = total area of ecosystem i (km ) and mangroves and seagrass beds with respective areas of 2 2 PCO = average price of a tonne of CO (€). 342 km (Andréfouët et al. 2008), 8.5 km (UICN 2 2 The production of fish biomass is calculated from 2015) and 7.6 km (Loricourt 2005 – see Figure 1). the estimated value of catchable (and marketable) Coral reefs comprise barrier reefs (266 km – 208 km), biomass using the following equation: fringing reefs (47 km – 195 km) and internal lagoon reefs (30 km – 18 km) forming a double barrier in the PB ¼ B  T  E  VA (4) i i i i southwest of the island (Guilcher et al. 1965; with: Thomassin et al. 1989; Wickel and Thomassin 2005; PB = biomass production value for ecosystem i Andréfouët et al. 2008). The large area of coral reefs of (€/year), Mayotte comes from the geological history of the Figure 1. Geographical distribution of CRAE of Mayotte – Modified from Gigou et al. (2009). Copyright 2017 by Agence des Aires Marines Protégées. Adapted with permission. 24 E. TRÉGAROT ET AL. island and the subsidence effect (sinking of the island large surfaces during proliferation outbreaks under its own weight), causing the formation of the (Gérard et al. 2008;Gigou 2011). Beyond the pres- lagoon and the barrier reef. The lagoon area is four sures of natural origin, coral reefs (particularly, times the land surface (Thomassin et al. 1989;Mirault fringing reefs) are affected by demographic pres- and David 2009). The relief is the result of an intense sures, such as the deterioration of coastal water past volcanic activity. Sixty-three per cent of the sur- quality, hyper-sedimentation, trampling upon reefs face of Grande-Terre is characterised by slopes greater (shore fishing) and destructive fishing techniques. Thehealthstatusofcoral reefs(Wickel and than 15% and/or located at more than 300 m altitude. Mangroves spread over a linear strip of 76 km and Thomassin 2005;PARETO 2013)ofMayotte an area of 8.5 km , covering 30% of Mayotte coast (Figures 2 and 3) is generally coted as degraded, but some areas show high coral cover. (UICN 2013). They are only located in bays and the Urban development and expansion of human few flat areas of the coastal zone. The nomenclature of mangrove of Mayotte comes in four ecological activities along the coastline are the main factors of degradation of mangroves, including the accumula- assemblages, from land to the sea: salty marshes tion of macro waste and wastewater discharge of all (6%), rear mangroves (22%), central and internal foreshore mangroves (55%) and the pioneer fronts watersheds (Herteman 2010; Thongo 2016). According to the assessment criteria of the Red List of Sonneratia alba (17%). Eleven seagrass species have been found in of French ecosystems (UICN 2015), the salt marshes Mayotte. Generally multi-specific, 56% of seagrass (50 ha) and the rear mangrove (190 ha) are the most threatened habitats, ranked ‘Critically Endangered’ beds are located near the barrier reef on the eastern part of Mayotte, 39% close to the fringing reefs of (CR). The central and internal foreshore mangroves Grande-Terre and 5% around Mtsamboro and (465 ha) are classified as ‘Least Concerned’ (LC). The pioneer fronts of Sonneratia alba (141 ha) are listed Karoni islets (Loricourt 2005). They thrive on sandy substrates outside reef flats areas but the depth of the ‘Vulnerable’. Jeanson (2009) evaluates the regression lagoon (30 to 45 m) does not offer optimal light of mangrove surfaces by 5.5% between 1950 and 2003 conditions for the development of the Indian Ocean (Figure 4). seagrass species. Finally, the seagrass ecosystems, poorly studied in Mayotte, with the exception of specific feeding grounds for the green turtle populations, Chelonia mydas Health status of coral reef and associated (Ballorain et al. 2010), show signs of deterioration that ecosystems cannot yet be specified. The deterioration of water qual- ity, hyper-sedimentation and trampling, are, in this The health status of coral reef varies according to respect, the main threats from human activities. The geographical sectors related to the 1998 and 2010 crossover study between the distribution of seagrass bleaching events (Nicet et al. 2012;Erikssonetal. beds and the quality of water bodies highlighted that 2013). Beside, the crown-of-thorn starfish 7.6 haand296.4hectaresofseagrassbedsare subjected (Acanthaster planci) that feed on corals destroy Figure 2. Health status of the barrier reef (% of coral cover) by station and sector – Modified from PARETO (2013, p. 26). Copyright 2017 by PARETO. Adapted with permission. INTERNATIONAL JOURNAL OF BIODIVERSITY SCIENCE, ECOSYSTEM SERVICES & MANAGEMENT 25 Figure 3. Health status of the fringing reefs of Mayotte – Modified from Wickel and Thomassin (2005, p. 12). Copyright 2017 by Wickel J. and Thomassin BA. Adapted with permission. to water bodies of, respectively, poor and moderate attenuation rate ranges between 92.7 and 97%. quality (between Mamoudzou and Bandrélé), and Finally for the fringing reef, the average width is 456haare locatedinawater bodypresenting ‘good’ 425 m, and the coastal protection function is fulfilled ecological environmental conditions, as is the case of the at 93.4% to 97.4% depending on the coral cover lagoon and offshore water masses (Figure 5). (Table 4). Surface data and health status from each ecosys- The biomass production service is not weighed in tem is synthesised in Table 3. the case of coral reefs as the fish biomass assessment is based on actual fish assemblage data in the current state of the ecosystem. This is a direct measurement. Production functions and weighting factors Mangroves The level of ecosystem services varies according to the Weighting factors for mangroves follow the vulner- health status and/or the vulnerability of ecosystems. ability criteria from UICN (2015). Each vulnerability class is assigned a weight that is used in the moneti- Coral reefs sation of the coastal protection, water purification The weighting calculations for coral reefs are com- and carbon sequestration services (Table 5). The plex. Indeed, as long as the physical structure of the fish biomass is a direct estimate from aerial visual reef remains, coastal protection function is poorly census (Guezel et al. 2009) and Djarifa fishing statis- affected by the health status of the ecosystem and tics in Mayotte (Jamon et al. 2010). weighting factors are never below 90%, despite low coral cover. The average outer barrier reef width is 1150 m, what influences also coastal protection. Seagrass Efficiency varies between 95.5 and 98.5% depending The weighting factors for seagrass beds are based on on the coral cover. For the inner barrier, the average the ecological state of the water bodies presented in width of the reef is 360 m and wave energy Figure 5. For instance, a seagrass patch located within 26 E. TRÉGAROT ET AL. Figure 4. Evolution of mangrove surfaces (ha) over the 1950–2003 period. The seaward arrows illustrate growth of mangroves; the landward arrows represent a regression of mangroves areas – Modified from Jeanson (2009, p. 146). Copyright 2017 by M. Jeanson. Adapted with permission. a water body of moderate quality will be assigned a Seagrass beds reduce waves’ energy by 40% weighting factor of 0.6 (Table 5), used in the mon- (Fonseca and Cahalan 1992; Christianen et al. 2013). etisation of production functions. Using the same value transfer mode than the one used for reefs, the annual value of coastal protection reaches € 63907/km according to the weight factors described in Table 5. Monetary value of ecosystem services Spurgeon et al. (2004) and Cooper et al. (2009) put Coastal protection service forward replacement values of mangroves by respec- The cost of installation of a breakwater system is tive artificial structures of € 254,559/km /year in approximately € 4000/m (France 2014 – GDP/cap.: Samoa (GDP/hab: € 2126) and € 239,204/km /year € 25846) with an annual maintenance cost equivalent in Belize (GDP/hab: € 4219). Considering an average to 4% of the installation cost (Balouin et al. 2012). value of € 88.2 per GDP unit, the value of coastal Taking into account the import taxes of 30% and the protection service of mangroves in Mayotte reaches amortization over 10 years of the structure, the annually € 491,077/km , taking into account the GDP annual cost is € 728/m or € 728,000/km. The transfer per capita during the transfer of value and health of value based on the GDP per capita (€ 7900 in status of mangroves (Table 5, supra). 2014) and taking into account of the weighting fac- The ‘optional’ values of coastal protection provided tors (Table 5) results in an annual cost of € 222,518/ by mangroves and seagrass reach, respectively, € 4.2 km. Overall, monetary values of coastal protection by million/year and € 2.7 million/year. Reported to the coral reefs reach about € 45.1 million/year for the km of each ecosystem, fringing reef has the highest outer barrier, € 3.8 million/year and € 40.9 million/ value (869 K€/year), while barrier reef and inner bar- year, respectively, for inner and fringing reefs where rier reef have respective values of 169 K€/year and these values are considered optional (Table 6). 127 K€/year. Finally, mangroves and seagrass have INTERNATIONAL JOURNAL OF BIODIVERSITY SCIENCE, ECOSYSTEM SERVICES & MANAGEMENT 27 Figure 5. Distribution of seagrass areas in Mayotte and environmental status of coastal water bodies – Modified from Loricourt (2005, p. 43), and PARETO, ASCONIT (2013, p. 143). Copyright 2017 by Loricourt A., PARETO and ASCONIT. Adapted with permission. Table 3. Summary of surface data and health status of coastal ecosystems in Mayotte (Indian Ocean). Coral reef Coral cover % 0–56–10 21–50 51–80 >80 Area (km)96 84 51 47 21 Mangroves Vulnerability CR EN VU NT LC Area (km ) 2.40 - 1.41 - 4.65 Seagrass Ecological state Bad Poor Moderate Good High Area (km ) - 0.076 2.96 4.56 - Table 4. Weighting of coastal protection service associated to coral reefs of Mayotte (Indian Ocean). Type of reef Outer barrier Inner barrier Fringing reef Reef flat width (m) 1150 360 425 Coral cover (%) Linear (km) Weighting factors (%) Linear (km) Weighting factors (%) Linear (km) Weighting factors (%) 0–5 45 95.5 0.8 92.7 71.2 93.4 6–20 36 96.0 4.2 93.3 70.6 94.0 21–50 22 96.8 3.1 94.4 41.9 95.1 51–80 27 97.8 3.1 95.9 11.1 96.4 >80 11 98.5 6.8 97.0 0.2 97.4 Coral cover on the barrier and the reef flat are considered equal. 28 E. TRÉGAROT ET AL. Table 5. Weighting of ecosystem services of mangroves and seagrass of Mayotte (Indian Ocean). Mangroves Seagrass Ecosystem Vulnerability Area (ha) Ecological state Area (ha) Weighting factors (%) Health status CR 240 Bad – 20 EN - Poor 7.6 40 VU 141 Moderate 296.4 60 NT - Good 456 80 LC 465 High – 100 CR: Critically endangered; EN: Endangered; VU: Vulnerable; NT: Near Threatened; LC: Least Concerned (UICN 2015). Ecological state according to water masses quality (PARETO, ASCONIT 2013). values per km of 491 K€/year and 353 K€/year, data on the water purification by algae, it is difficult respectively. to quantify the weighted value. It is likely that the real value of water purification by coral reefs with nearly 60% algal cover is substantially higher. Water purification service Mangroves water purification represents up to € Coral reef organisms have limited ‘water purification’ 1.6 million/year, with a value per unit area of 191 K capabilities, evaluated by De Groot et al. (2012)toUS 2 2 €/km /year, well below that of seagrass beds which is $ 8500/km /year, or € 7752/km /year (Table 6). € 1.2 million/km /year. The monetary value of the As reported by Lal (2003), the value of treatment of water purification service provided by seagrass beds inland waters by mangroves in Fiji represents € 2 in Mayotte reaches almost € 9.5 million/year. 174,200/km /year for a GDP/capita of € 5078 in 2003. According to the transfer of values for Carbon sequestration Mayotte, and the health status of mangroves, the Considering the stock market value of a tonne of CO value of water treatment by mangroves reaches equal to € 6.12 (2015) and the values of net produc- annually € 191,435/km . tivity of mangroves (3667 tCO eq/km /year) and sea- According to Costanza et al. (1997), the value of the grass (435 tCO eq/km /year), monetary values of water purification service produced by seagrass beds is carbon sequestration for these two ecosystems are, US$ 19002/ha/year or € 1,732,255/km /year (Table 6). respectively, 134 K€/year and 15 K€/year. The value This result is to be interpreted with caution because it of carbon sequestration per km for mangroves is 8.3 is the only existing value from the literature without times that of seagrasses (€ 15853 against € 1911). This clarification on the monetary valuation of this service difference is explained by the size of the plants struc- (Barbier et al. 2011). If we consider the weighting turing each ecosystem. factors (Table 5), the value of water purification for seagrass beds is € 1,243,759/km /year. The values of water purification services vary Fish biomass production greatly according to ecosystems. Coral reefs have a The average biomass of commercial fish species of total value of € 2.7 million/year, but in the absence of Mayotte coral reefs is estimated at 95.8 g/m (Wickel Table 6. Monetary values of ecosystem services provided by CRAE of Mayotte (Indian Ocean). Length Area 2 2 Ecosystem services (km) (km ) Max Unit value Monetary value (€/year) Value per km (€/year) Coastal Protection Outer barrier reef 210 266 222,518 €/km 45,089,035 169,508 Optional values Inner barrier 18 30 222,518 €/km 3,816,249 127,208 Fringing reefs 195 47 222,518 €/km 40,861,390 869,391 Mangroves - 8.46 695,200 €/km 4,154,515 491,077 Seagrass 42 7.6 89,007 €/km 2,684,095 353,170 Water treatment Coral reefs 342 7752 €/km /year > 2,651,184 > 7752 Mangroves 8.46 271,008 €/km /year 1,619,544 191,435 Seagrass 7.6 1,732,255 €/km /year 9,452,569 1,243,759 Carbon sequestration Coral reefs 342 - - - Mangroves 8.46 22,442 €/km /year 134,113 15,853 Seagrass 7.6 2662 €/km /year 14,527 1911 Fish Biomass Production Coral reefs 342 120 t/km /year 92,340,000 270,000 Mangroves 1.41 25 t/year 75,000 53,191 Seagrass 7.6 1 t/km /year 16,370 2154 Value of a tonne of CO in the stock market: 6.12 € (September 2015). The value added per kilo of fish is € 3 (Own survey 2015). INTERNATIONAL JOURNAL OF BIODIVERSITY SCIENCE, ECOSYSTEM SERVICES & MANAGEMENT 29 et al. 2005) and 82.8 g/m for the stations of the Coral statuses. The total VUI would be € 188 million if Reefs Observatory (Chabanet 2002). The average ecosystems were in pristine conditions, which repre- 2 2 value is either 90 g/m sents € 37 million more. Considering the optional or 90 t/km for all the reefs of Mayotte. coastal protection values, the total economic value The evaluation of fish biomass in mangroves is would be € 245 million for ecosystems in very good based on traditional fishery: djarifa fishing, exclu- condition, that is, € 42 million more than the current sively women practice. The fishing gear, the ‘lamba’, value of € 203 million. is similar to a beach senne with a much smaller mesh. The fishing practice gathers a team of three to nine women for one to three djarifas. They target small Discussion pelagic and juvenile fish out of mangroves, within protected bays and on the reef flat at low tide The deterioration of ecosystem health status changes (Jamon et al. 2010). The average number of djarifa the amount of services produced. However, services are not affected in the same way, as a specific func- fishing trips in Mayotte was estimated at 1092 per year in 2009, of which 70% in mangroves (Guezel tion can increase in degraded ecosystems. This para- et al. 2009) or 764 djarifa fishing/year. According to dox is especially true for water purification and carbon sequestration services provided by coral Jamon et al. (2010), the average weight of the catches of one fishing trip in mangroves is 32.8 ± 10.4 kg, or reefs. When coral reefs are degrading along with an annual total of approximately 25 ± 8 t/year algal overgrowth, the production functions increase due to the macroalgae capacities for water purifica- (Table 6). (Gullström et al. 2002) found that the exploited tion and carbon absorption. However, the coastal biomass of seagrass fish in Mozambique is protection and biomass production functions are, respectively, hardly and moderately impacted by approximately 1 t/km /year. When transposed to coral coverage as long as the physical structure of Mayotte and by applying weighting factors the reef remains. Indeed, coral reef organisms have (Table 5), the exploitable biomass accounts 0.72 t/km /year. limited or negligible ‘water purification’ abilities com- pared to seagrass beds (Costanza et al. 1997;De The total biomass production value for coral Groot et al. 2012). However, algae overgrowth, reefs reaches 92 M€/year, much higher than the values for mangroves and seagrass beds, respec- usually leads to the reduction of live coral cover (Hughes 1994; McManus et al. 2000; Mumby 2009), tively, 75 K€/year and 16 K€/year. but contributes positively to water purification by The value per unit area (km ) helps to show the absorbing part of the nutrients (Lapointe 1997). real marketable fishery potential of each ecosystem, Considering the steep growth of macroalgae induced reefs having the highest value (270 K€/year) com- by the enrichment of coastal waters with nutrients pared to mangroves (53 K€/year) and seagrass beds and their ability to absorb excess nitrates and phos- (2 K€/year). phates, the water purification service provided by The economic value of indirect uses is estimated at degraded reef ecosystems will increase. A high eco- € 151 million/year, of which € 140 million originates from coral reefs only, € 1.8 million from mangroves nomic value, not quantifiable in the present state of and € 9.5 million for seagrass (Table 7). knowledge, is then allocated to a service provided by a degraded state of the original ecosystem. This pro- Coastal protection and biomass production are the two major ecological services, followed by the sea- duction function would be minimal in a healthy reef grass water purification capacity. Optional values ecosystem. It exists thereupon only because of the degradation of the ecosystem under pressures of associated with coastal protection from inner and fringing reefs, mangroves and seagrass add € 52 mil- anthropic origins. Carbon absorption by algae lion. By reporting the IUV per km through photosynthesis is unequivocally proven and of ecosystem, even comparable to that of seagrasses (Beer and Koch seagrass rank first with the highest value (€ 1.2 mil- 1996; Hanelt et al. 2003) while it is questioned on lion/km /year), followed by coral reefs (€ 0.4 million/ 2 2 healthy reef formations (Shaw et al. 2015). Eutrophic km /year) and mangroves (€ 0.2 million/km /year). These values reflect ecosystems in various health conditions in coastal waters of Mayotte promote algal Table 7. Overview of maximum IUVs and monetary IUVs gathered for the CRAE or Mayotte (Indian Ocean). CR M S Total Options Total + options IUV max 172.5 M€ 2.6 M€ 13.2 M€ 188.3 M€ 57.0 M€ 245.3 M€ IUV calculated 140.1 M€ 1.8 M€ 9.5 M€ 151.4 M€ 51.5 M€ 202.9 M€ % 81% 71% 72% 80% 90% 83% Total loss 32.4 M€ 0.7 M€ 3.7 M€ 36.9 M€ 5.5 M€ 42.4 M€ IUV/km 0.4 M€ 0.2 M€ 1.2 M€ 0.4 M€ 0.6 M€ 0.6 M€ 30 E. TRÉGAROT ET AL. total loss of coral cover leads to a reduction of 39% growth; the function of carbon sequestration of reef fishery landings in Eastern Indonesia. increases accordingly, as does the monetary value of this service. McClanahan et al. (2016) found that natural fish biomass in pristine coral reefs in the Western Pascal et al. (2014) evaluated the carbon sequestra- Indian Ocean can reach 120 t/km tion service for Mayotte at € 2,380,000. In this article, . Using this later the evaluation is based solely on the absorption of value, the maximum monetary value of fish biomass carbon dioxide, not taking into account the amount production in Mayotte reaches € 123 million, that is, of carbon that has been stored for hundreds of years € 31 million more than the monetary value of € 92 in the soil. Consequently, the value in this paper is 16 million obtained. Pascal et al. (2014) evaluated the times lower than the previous stated value: € 148,640. commercial biomass production service for both Valuation of carbon sequestration service varies commercial and self-consumption fisheries related greatly in the literature. The reason is the number to CRAE such as coastal fisheries, deep-sea fishing of compartments to valued (soil and/or living bio- and supervised sport fishing and reached an annual mass) and the number of processes (carbon storage value of € 9,180,500. Our results refer to the fish and/or carbon absorption) included in the evaluation. biomass production (of which a portion forms also Also, one of the major factors is to determine the a provisioning service as part of the biomass sub- value of one ton of carbon dioxide. According to jected to fishing) and represent the ecosystem ability Canu et al. (2015), the value of one ton of CO to produce exploitable fish biomass worth is € 92,340,000 per year, which significantly differs € 19, which appears to be very conservative compared to the value of € 97/tCO reported by Van Den Bergh from the previous cited report value. Mangroves and seagrass beds of Mayotte actively and Botzen (2014). In this article, the current market contribute to the purification of coastal waters and nutri- price is the reference (€ 6.12 in 2015). Degradation of coral substrate and erosion of reefs ent absorption. This ecosystem service generates the highest monetary value (respectively, € 1.6 million and are rather slow mechanisms: the changes occurring in ecosystems neither affect entirely the coastal protec- € 9.5 million, representing 89 and 99% of the total value tion service (Sheppard et al. 2005), nor the biomass of indirect use services provided by these ecosystems). However, even if these ecosystems absorb excess nutri- production (Ainsworth and Mumby 2015). Other parameters influence the production of the service ents, the fact remains that poor water quality negatively such as the presence of a barrier reef and the extent impacts their functioning. According to Herteman (2010), the wastewater effect on mangrove crabs popula- of the reef flat (Ferrario et al. 2014). Degraded coral reef communities hardly affect wave energy attenua- tion in Mayotte translates into a modification of the tion, reducing it by 10% maximum (Sheppard et al. nitrification/denitrification process (bioturbation) and over time significantly perturbates the mangrove ecosys- 2005). The weighting by the health status is therefore not significant; the associated value remains high tem. For seagrass beds, excess nutrients favours algae accordingly. Services of coastal protection and carbon growth at the cost of seagrass plants (Duarte 2002). Besides the need to maintain production func- sequestration are discussed in Pascal et al. (2014). Although very interesting, they used a detailed tionsby implementingspecificmeasurestomiti- experimental approach based on the evaluation of gate or even annihilate the effects of human avoided cost. As a result, coral reefs that would pro- activities, coastal ecosystem preservation also tect highly urbanized areas are worth much more requires conservation of iconic species, some of than coral reef protecting pristine coastal habitats which are listed on the red list of UICN. Seagrass without any human infrastructures. In other words, beds are important feeding areas for dugongs if there is no infrastructure to protect, coral reef is (Dugong dugong – Vulnerable), less than 10 indivi- worth nothing in terms of coastal protection, which is duals remain in the lagoon of Mayotte (Pusineri a very limiting approach. As a result, Pascal et al. et al. 2013), green turtles (Chelonia mydas – (2014) evaluated the coastal protection in Mayotte at Endangered) and, to a lesser extent, hawksbills tur- € 10.5 million while in our article the value reaches € tles (Eretmochelys imbricata – Critically 45.1 million. Endangered). In this context, the preservation of The progressive and rapid shifts between coral dense and healthy seagrass beds is a key issue, dominant communities and dense algal populations associated to strong regulations to limit poaching affect the structure of fish communities in coral reefs and risks of collision with boats. The decline of (Wilson et al. 2006), but not necessarily the biomass. seagrass beds has much more serious and durable The complex three-dimensional structure of the reef consequences than the sole disappearance of this is determining for the presence of dense fish popula- ecosystem (Waycott et al. 2009), given the close tions. The proportion of herbivorous fish is increas- relationship with associated ecosystems. ing in algae dominated environments. According to The marine and coastal environments of Mayotte Ainsworth and Mumby (2015), it appears that the have been deteriorating for several decades. Between INTERNATIONAL JOURNAL OF BIODIVERSITY SCIENCE, ECOSYSTEM SERVICES & MANAGEMENT 31 species richness. Therefore, nutrient loading is a key 1989 and 2004 (15 years), the coral cover of fringing parameter to control, prior to protect coastal marine reefs has decreased by 60% (Wickel and Thomassin 2005), while between 2005 and 2013 (8 years) that of ecosystems. Protection of CRAE is a major challenge for the barrier reef has shrunk by 15% (PARETO 2013). island of Mayotte in the current context of uncon- Degradation also occurs in mangroves where Sonneratia pioneer fronts have diminished by 43 ha trolled urbanisation of the coast (PADD 2008). in 30 years (Jeanson 2009). Such changes affect the production functions of ecosystems. For pristine coastal environments, the maximum value of these Conclusion services would reach € 188 million/year (up to € 245 million with optional values of coastal protection). The total value of indirect uses provided by CRAE of Given the actual state of degradation of ecosystems, Mayotte reaches € 176 million/year. This amount is the IUV calculated (€ 151 millions) is € 37 million significant to the local economy of Mayotte since it is lower than the optimal value. If we consider the higher than the added value generated by the agricul- optional values, the IUV calculated reaches € 203 ture: 95 M€, the industrial: 57 M€ or the construction million (€ 42 million lower than the optimal value). sector: 135 M€ (INSEE 1975–2017). The estimated The gradual degradation of ecosystem health in values of coastal protection (€ 30 million) and biomass recent years is the principal reason. Natural events production (€ 81 million) by coral reefs and those of such as increased water temperature leading to coral water purification services provided by mangroves (€ bleaching, hurricanes and proliferation of crown-of- 1.6 million) and seagrass beds (€ 9.5 million) emphasise thorn starfish Acanthaster had major contribution to the economic interest in conservation efforts for the the changes observed. However another factor, much preservation and restoration of ecosystems. Coral reefs more significant, is imputable to public inaction, that contribute to 91% of the economic value derived from is, the lack of political consideration, laissez-faire the four ecosystem services presented in this article. attitudes and the deficient interest in understanding However, the ecosystem with the highest monetary the ecological and economic functions of value, relative to one square kilometre, is seagrass marine coastal environments. Thus, overall the lack- beds (€ 1.2 million), followed by reefs (€ 0.4 million) ing € 37 million/year in services may be interpreted and mangroves (€ 0.2 million). as the cost of public non-intervention in Mayotte Human activities contribute to the degradation of CRAE management. Mayotte CRAE including remote reefs, located more The results of the Mayotte study have been pre- than 10 km away from the coast. One third of these sented to the Environment, Planning and Housing reefs have a coral cover between 0 and 20%. This Directorate. The economic development of Mayotte assessment is worrying in a context of economic is a priority, which relegates environmental impera- development and increasing risks of degradation. tives in the background. The same observation can be Consequently, the economic loss from indirect use made currently to all French Overseas Collectivities values reaches € 32 million. where IFRECOR works. The lack of understanding This study highlights the close link between environ- and additional mechanisms to integrate economic mental conservation and economic valuation challenges, evaluations in the decision-making process makes and should provide support for future policy decisions unlikely the use of the results of such work, and on coastal management and marine environmental pro- constitutes a very critical issue for the marine park tection. The paradox highlighted that a higher monetary of Mayotte. value is assigned to a deteriorating ecosystem, however, It is expected that the IUV will continue to shows the limits of the economic evaluation. It is there- decrease in the near future because too little is done fore necessary to accompany the results with interpreta- to counter pollution by sewage releases. In 2015, only tion elements, essential to public decisions. the Mamoudzou municipality was equipped with a Several lines of study can be sketched in this functional water treatment plant which can process regard. This involves, for example, quantifying the discharges of 10000 inhabitants, while the total popu- water purification function by seagrass beds, but lation of the island exceeds 235,132 inhabitants. The also by algae that are becoming particularly impor- shortage of water treatment therefore degrades the tant among reef communities. In order to monetise coastal water quality, meaning the presence of heavy this service, it is necessary to estimate (1) the absorp- metals, polyaromatic hydrocarbons and polychloro- tion rate of nutrients by an ecosystem or organism biphenyls (Thomassin et al. 2010). According to and (2) the replacement cost of a technological arte- Duprey et al. (2016), eutrophication of coastal waters fact (water treatment plant) for an equivalent water causes a decrease in coral cover and a decrease in treatment level. 32 E. TRÉGAROT ET AL. Bridge TC, Hughes TP, Guinotte JM, Bongaerts P. 2013. Acknowledgements Call to protect all coral reefs. Nat Clim Change. 3:528– This study was conducted under the theme of transversal interest ‘Total economic value of coral reefs and associated Burke L, Reytar K, Spalding M, Perry A. 2011. Reefs at risk ecosystems of the French overseas territories’ of IFRECOR . revisited. Washington (DC): World Resources Institute. The authors thank the DEAL Mayotte, the General Council Cabral P, Levrel H, Schoenn J, Thiebaut E, Le Mao P, of Mayotte, the University of Mayotte, and the Marine Park Mongruel R, Rollet C, Dedieu K, Carrier S, Morisseau of Mayotte for providing all completed studies of these F. 2015. Marine habitats ecosystem service potential: a ecosystems, their health status and the pressures, and vulnerability approach in the Normand-Breton (Saint developed the economic and environmental issues in Malo) Gulf, France. Ecosyst Serv. 16:306–318. Mayotte. Finally, the authors would like to thank Claire Canu DM, Ghermandi A, Nunes PA, Lazzari P, Cossarini Montocchio and Christopher Martin for their help in G, Solidoro C. 2015. Estimating the value of carbon proofreading and translating this paper. sequestration ecosystem services in the Mediterranean Sea: an ecological economics approach. Global Environ Chang. 32:87–95. Chabanet P. 2002. Coral reef fish communities of Mayotte Disclosure statement (western Indian Ocean) two years after the impact of the 1998 bleaching event. Mar Freshwater Res. 53:107–114. No potential conflict of interest was reported by the Christianen MJ, van Belzen J, Herman PM, van Katwijk authors. MM, Lamers LP, van Leent PJ, Bouma TJ. 2013. 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Journal

International Journal of Biodiversity Science, Ecosystem Services & ManagementTaylor & Francis

Published: Nov 29, 2017

Keywords: Indirect use values; ecosystem services; coral reefs; mangroves; seagrass beds; Mayotte; Indian Ocean

References