Mangrove ecosystems in Sri Lanka are increasingly under threat from development projects, especially aquaculture. An economic assessment is presented for a relatively large (42 ha) shrimp culture development proposed for the Rekawa Lagoon system in the south of Sri Lanka, which involved an extended cost-benefit analysis of the proposal and an estimate of the "total economic value" (TEV) of a mangrove ecosystem. The analysis revealed that the internal benefits of developing the shrimp farm are higher than the internal costs in the ratio of 1.5:1. However, when the wider environmental impacts are more comprehensively evaluated, the external benefits are much lower than the external costs in a ratio that ranges between 1:6 and 1:11. In areas like Rekawa, where agriculture and fisheries are widely practiced at subsistence levels, shrimp aquaculture developments have disproportionately large impacts on traditional livelihoods and social welfare. Thus, although the analysis retains considerable uncertainties, more explicit costing of the environmental services provided by mangrove ecosystems demonstrates that low intensity, but sustainable, harvesting has far greater long-term value to local stakeholders and the wider community than large shrimp aquaculture developments.
"Although 25 percent of all mangroves occur in protected areas, rates of loss appear highest in less developed countries where mangroves are being cleared for coastal development, aquaculture, timber, and fuel production (Spalding et al., 2014). The case for the importance of retaining mangrove forests has focused on the multiple social and economic benefits that are likely to be derived from the range of ecosystem services that they provide: fisheries, carbon cycling and sequestration, water purification, and high biodiversity (e.g., Sathirathai and Barbier, 2001; Gunawardena and Rowan, 2005; Barbier et al., 2011; Hutchison et al., 2014). A particularly strong argument, however, has been made for mangrove protection and management through their potential role as dissipaters of incident wave energy (e.g., Badola and Husain, 2005), in relation to storm surges, and in response to tsunami impacts, the last of these three being brought into sharp focus by the Asian tsunami of December 2004. 1 The mixed messages from the attempts to assess the role of mangroves in mitigating the impact of this tsunami event (e.g., Cochard et al., 2008) provide one example of the underpinning lack of basic information regarding the level of coastal protection that mangrove forests can provide in the face of coastal hazards. "
[Show abstract][Hide abstract] ABSTRACT: Risks from coastal hazards to people and property are expected to increase with near-future sea level rise, changes in storminess, and increasing coastal populations. Evidence from empirical and modeling studies suggests that mangrove forest vegetation can reduce storm surge peak waters levels where mangroves are present over sufficiently large areas. Mangroves are best used alongside other risk reduction measures (embankments, early warning systems) to ensure the lowest possible level of residual risk.
Coastal and Marine Hazards, Risks, and Disasters, 12/2015: pages 403-429; , ISBN: 9780123964830
"Many small-scale farmers took on farming, leading to an expansion of shrimp aquaculture. Small-scale farmers continued to farm within their community areas, while large and medium-scale farmers shifted from place to place by converting mangrove  and coconut cultivating lands into shrimp farms . Low stocking densities of shrimp postlarvae (PL) in small-scale farms (7–12 PL/m 2 ) compared to that of large-and medium-scale farms (12–25 PL/m 2 ) cause less disease incidences in small-scale farms and also lower operation cost in small-scale farms than in other farms bring about high profit margins per unit area in small-scale farms . "
[Show abstract][Hide abstract] ABSTRACT: Shrimp aquaculture in northwestern Sri Lanka shows co-management like features. To understand the reasons behind co-management and to identify the mechanisms by which co-management is carried out, the paper examines shrimp aquaculture operations in three coastal communities using a case study approach. Water from an interconnected lagoon system is the key input for shrimp ponds, but it is also the potential source of shrimp disease outbreaks that threaten all shrimp farms. Farmers try to prevent the spread of disease by co-operating to adjust the timing of water intake and wastewater release. This is done through a zonal crop calendar system which is developed and implemented by a vertically integrated institutional structure with three levels: sub-zonal/community, zonal, and national. Partnerships, overall sharing of power and authority, and learning-by-doing are key features of this collaborative management system. The case shows that adaptive co-management can develop through collaborative problem-solving over time, even in the absence of legal arrangements.
"Rapid losses of mangroves make it crucial to inventory and monitor the remaining mangroves to protect them from harmful development (Blasco, Aizpuru, & Gers, 2001; Gunawardena & Rowan, 2005; Terchunian et al., 1986). Mapping and quantifying the structure and biomass of mangrove ecosystems on a large scale is also important for studies of carbon storage, biodiversity, forest quality, and habitat suitability . "
[Show abstract][Hide abstract] ABSTRACT: Tidal wetlands are highly productive and act as critical habitat for a wide variety of plants, fish, shellfish, and other wildlife. These ecotones between aquatic and terrestrial environments also provide protection from storm damage, run-off filtering, and recharge of aquifers. Many wetlands along coasts have been exposed to stress-inducing alterations globally, including dredge and fill operations, hydrologic modifications, pollutants, impoundments, fragmentation by roads/ditches, and sea level rise. For wetland protection and sensible coastal development, there is a need to monitor these ecosystems at global and regional scales. Recent advances in satellite sensor design and data analysis are providing practical methods for monitoring natural and man-made changes in wetlands. However, available satellite remote sensors have been limited to mapping primarily wetland location and extent. This paper describes how the HyspIRI hyperspectral and thermal infrared sensors can be used to study and map key ecological properties, such as species composition, biomass, hydrology, and evapotranspiration of tidal salt and brackish marshes and mangroves, and perhaps other major wetland types, including freshwater marshes and wooded/shrub wetlands.
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