A new report commissioned by Wetlands International for the first time quantified the provision of mangrove ecosystem services according to different management regimes. The study concludes that ecosystem service provision depends strongly on the type of management and that mangrove-rich management regimes generally outscore aquaculture regimes. Decision-makers can make management choices depending on the desired outcome in terms of ecosystem services.
This new report, published by Wageningen University and Wetlands International, seeks to fill a significant gap in mangrove ecosystem service estimates. The analysis conducted for the report served as the basis for a peer reviewed article on the journal Ocean & Coastal Management.
While several studies have sought to measure and value the ecosystem services provided by mangrove ecosystems in general, this new piece of research has for the first time conducted separate evaluations for zones that are characterised by distinct management activities – so-called ‘management regimes’, which include protected, rehabilitated, silvo-fishery and converted mangrove systems.
Natural mangroves were found to score highest for all 7 evaluated ecosystem services except food, which scored only fractionally lower than aquaculture. Conversely, mangroves converted for aquaculture received the maximum score for food production, but this coincides with low or even negative provision of all other ecosystem services. Such disservices include high carbon emissions, wave height increase (increasing flood risk) and water pollution. Mangrove plantations and silvo-fisheries, which combine ecosystem rehabilitation with the provision of raw materials and shrimp, respectively, also outscore mangroves converted for aquaculture. This clearly indicates the merits of restoring mangroves formerly used for intensive land use.
By assessing the effects of management regimes in the provision of a whole suite of 7 ecosystem services, the study contains significant policy and management-relevant messages. Furthermore, by comparing various mangrove regimes to aquaculture the study also for the first time enables decision-makers to explore the crucial elements of optimal coastal management, by considering which management regime will result in the provision of which bundle of ecosystem services.
The new management typology introduced by the study is innovative in that it takes into account policy, legislation and management activities in Java (Indonesia), while the regimes’ ecological characteristics (resulting from management) can be used to deduce ecosystem service provision.
Some of the study’s findings include:
- All management regimes with some mangroves outperform aquaculture regimes in terms of number of ecosystem services provided.
- Aquaculture only provides one single service (food provision), but this largely depends on artificial production and jeopardizes other services (carbon storage, coastal protection, water purification).
- Although aquaculture systems (almost entirely artificial) and mangrove systems (natural) are difficult to compare, the study found that fishery yields in more natural mangrove systems compare in magnitude (in terms of kg/ha/yr) to aquaculture, while also providing additional benefits. However, this may entail a wide variety of species in the case of mangroves while aquaculture delivers specific target species.
- Mangrove tree age (and related height, diameter, root length, species richness and structural complexity) were found crucial for all seven ecosystem services analysed in the study.
- There are at least 9 varieties of silvo-fisheries, which differ widely in terms of ecosystem service provisioning. The ones that perform best have separate inlets and outlets, and separate parts for forestry and fishing, which optimises functionality.
- Eco-certification has great potential (in view of greenbelt and rehabilitation requirements) but can still have negative impacts on other services unless management is adjusted.
The study describes state and performance indicators for 7 ecosystem services: food, raw materials, coastal protection, carbon sequestration, water purification, nursery for fish and shrimp, and nature-based recreation. The typology of management regimes is based on 10 specific management characteristics and indicators, taking into consideration local variation in Javanese legislation and management activities, and includes 8 ecological characteristics. The study assumes a stable situation over time, not taking into account possible exhaustion of a system.
Recent studies have assigned monetary values to mangrove ecosystems as a whole (often including mangroves converted for aquaculture), but this report sought to also quantify and compare ecosystem services for which no valuations are currently possible. The study’s findings are based on a combination of literature review and rapid field assessments.