MEPS 278:77-88 (2004)  -  doi:10.3354/meps278077

ABSTRACT: Mangrove epifaunal communities have access to various carbon and nitrogen sources and we hypothesized that the degree of material exchange with the aquatic environment might influence the overall use of different substrates by intertidal communities. Therefore, we analyzed C and N stable isotope ratios in primary producers, sediments and 245 samples of epifauna hand-collected from 5 sites in India, Sri Lanka and Kenya (representing estuarine, lagoonal and basin-type mangrove forests). Several patterns emerged from this data set. First, epifaunal communities used a range of available food substrates at all sites studied, including mangrove-derived organic matter, local microphytobenthos and micro-epiflora, as well as imported C and N from the aquatic environment (i.e. phytoplankton- and/or seagrass-derived organic matter). Secondly, our data indicate that at sites with significant inputs of aquatic sources, use of mangrove carbon is rather limited on a community basis, whereas in systems with less material exchange with adjacent waters, the relative importance of mangroves is higher. Thus, despite the unquestionable impact some epifaunal species may have on leaf litter dynamics, the dependency of the invertebrate community as a whole on mangrove litter is not ubiquitously large and varies according to the availability of local versus tidally imported sources. Precise quantification of the relative importance of different substrates with δ¹³C and δ¹⁵N is, however, not always straightforward due to the multitude of available sources and the overlap in source stable isotope signatures. Micro-epiflora on mangroves trees were remarkably depleted in ¹⁵N in all systems (δ¹⁵N between -8.2 and -2.4‰) and thus form an example where δ¹⁵N is a useful source indicator, as low δ¹⁵N values of several gastropod species indicated substantial feeding on such epiflora.

KEY WORDS: Sesarmid crab · Mollusk · Intertidal · Invertebrate · Foodweb · Stable isotope · Carbon · Nitrogen