Prioritising Mangrove Ecosystem Services Results in Spatially Variable Management Priorities

Abstract

Incorporating the values of the services that ecosystems provide into decision making is becoming increasingly common in nature conservation and resource management policies, both locally and globally. Yet with limited funds for conservation of threatened species and ecosystems there is a desire to identify priority areas where investment efficiently conserves multiple ecosystem services. We mapped four mangrove ecosystems services (coastal protection, fisheries, biodiversity, and carbon storage) across Fiji. Using a cost-effectiveness analysis, we prioritised mangrove areas for each service, where the effectiveness was a function of the benefits provided to the local communities, and the costs were associated with restricting specific uses of mangroves. We demonstrate that, although priority mangrove areas (top 20%) for each service can be managed at relatively low opportunity costs (ranging from 4.5 to 11.3% of overall opportunity costs), prioritising for a single service yields relatively low co-benefits due to limited geographical overlap with priority areas for other services. None-the-less, prioritisation of mangrove areas provides greater overlap of benefits than if sites were selected randomly for most ecosystem services. We discuss deficiencies in the mapping of ecosystems services in data poor regions and how this may impact upon the equity of managing mangroves for particular services across the urban-rural divide in developing countries. Finally we discuss how our maps may aid decision-makers to direct funding for mangrove management from various sources to localities that best meet funding objectives, as well as how this knowledge can aid in creating a national mangrove zoning scheme.

Fig 1. Central areas of the Fijian Archipelago (inset).

Greater than 95% of Fiji's mangrove areas occur on the islands of Viti Levu, Vanua Levu, Kadavu, and within the Lomaiviti Group. Dark polygons are mangrove areas mapped in this study.

Fig 2. Management objectives and associated mangrove management actions aimed at ensuring long-term provisioning of the ES.

Fig 3. Percent of total cumulative ES benefits versus the percent of overall opportunity costs when managing each mangrove ES service objective; red and blue lines indicate the priority and bottom 20%-by-area for each service.

Coloured polygons indicate the cumulative percent of the total number of mangrove associated species that would be protected by managing sites in order of their priority ranking.

Fig 4. Ranking of priority sites for coastal protection services.

Panel (a) (red inset polygon) centres on the greater Suva area; the darkest coloured areas are the highest ranked priority sites in Fiji. Panel (b) (blue inset polygon) centres on the Nadi and Lautoka area in the Western Division; populations are also high in the area, but many areas where mangroves may have existed have been cleared for coastal and resort development. Little development occurs behind extant mangroves in this area. Dark grey areas are corals reefs.

Fig 5. Priority sites for fisheries services.

The highest ranked priority site was found on north-eastern Vanua Levu (panel a, red inset polygon) but a large clumping of the highest ranking priority sites occurred north of the Rewa Delta (panel b, blue inset polygon) on eastern Viti Levu. Dark grey areas are coral reefs.

Fig 6. Priority sites for biodiversity services.

The highest ranked priority mangrove for biodiversity was actually within the town limits of Suva and was the second smallest mangrove stand mapped (530 m²; panel a, red inset polygon). Priority mangroves contrast greatly with mangroves having the highest overall biodiversity benefit (S), for example, around the Rewa Delta area (panel b, blue inset polygon). Dark grey areas are coral reefs.

Fig 7. Carbon storage priority mangroves.

The majority of the 19 priority areas were on the island of Vanua Levu, where population and development is generally lower (panel a, red inset polygon). Several large priority areas are found on Viti Levu, however; for example, around the large mangrove stands near the mouth of the Ba river (panel b, blue inset polygon). Dark grey areas are coral reefs.