TDA-IME Project Final Report June, 2013 Ranong Biosphere Reserve in Thailand, Macintosh et al. (2002) reported that more than 20 species of mangrove-associated molluscs were collected for food by local people. Some bivalves are also important on a commercial scale, for example cockles and clams that are abundant in the mudflats adjacent to mangroves. Oysters and mussels, found attached to mangrove roots, are also collected as food, while green mussels (Perna viridis) and the larger species of mangrove oysters are farmed commercially in suitable locations, including mangrove waterways. The consequences of mangrove clearing on the associated faunal community have been reported on for only a few species and locations (Ashton et al., 2003; Manson et al., 2005). Ashton et al. (2003) showed that management history and age of the mangrove forest stand played an important role in moderating crab community structure. They also showed that former tin-mining areas, former concession forests (for charcoal production), or abandoned shrimp ponds, rehabilitated by planting mangroves can recover in terms of crustacean and molluscan biodiversity. Rapid recolonization is possible because crustaceans and molluscs produce larval life stages with strong recruitment potential into the intertidal zone (Macintosh, 1984). In addition, adults can move into restored habitat from nearby mangrove sites (Ashton et al., 2003). Thus mangrove areas across borders may act as important sources of recruitment, with larger transboundary areas being more robust than smaller ones. To help overcome mangrove degradation and protect biodiversity, a network of protected areas would provide refuges for fish and invertebrate species that could then recolonize adjacent impoverished areas. Brachyuran crab and molluscan communities are ubiquitous throughout the mangroves of Indochina and an important component of coastal food webs. A high diversity of grapsoid crabs, especially sesarmids, may indicate good mangrove ecosystem health (Macintosh et al., 2002). One species may not be able to serve as an indicator alone, but changes in brachyuran crab community structure could be a useful tool for managers to monitor mangrove habitat status (Ashton et al., 2003). Mangrove crabs are good indicators of ecological integrity because of their high visibility and physical impact on mangrove soil structure. Their high recruitment potential into rehabilitated mangrove habitats also makes them potential indicators of ecosystem recovery. Crab abundance can be estimated directly when they are active at low tide, or indirectly by counting the density of their burrows. Other Benthic Fauna Mangrove sediments also support high densities of epibenthic, infaunal and meiofaunal invertebrates. The rich epifaunal communities on mangrove tree roots, trunks and branches include sponges, hydroids, anemones, polychaetes, bivalves, barnacles, bryozoans and ascidians. These organisms represent important food sources for other invertebrates and fish (Farnsworth and Ellison, 1996). The macrobenthos include annelids, polychaetes, oligochaetes and hydrozoans. The meiofauna (defined as organisms ranging from 53 to 1,000 μm) consist mainly of nematodes, copepods and protozoans. Meiofauna are widely distributed and abundant, but poorly studied. Thus, their biodiversity is likely to be much higher than has been recorded to date. The abundance of meiofauna can number in the millions per square metre of soil. They are heavily concentrated in the upper centimeter, with their numbers falling off rapidly below this soil depth (Somerfield et al., 1998). Meiofauna populations have high numbers of species and a high level of taxonomic diversity. Meiofauna are thought to be important in converting mangrove primary production to detritus and as a food source for many deposit-feeding or surface-grazing macrofauna. Crabs, mudskippers, penaeid shrimps and a number of fish species are reported to consume large quantities of meiofauna (e.g. Sasekumar, 1981). In conclusion, mangrove meiofauna are a little studied group of various animal taxa, but they can be regarded as an important component of the mangrove-coastal waters food web. 38
Transboundary Diagnostic Analysis of Indochina Mangrove Ecosystems
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