Role of microhabitats in food webs of benthic communities in a mangrove forest

Mangrove benthic macro-invertebrate communities have access to various food sources. The food web in this system may not be based on homogenous mangrove detritus. In order to determine the contributions of mangrove leaf litter and microalgae to the benthic macro-invertebrate community, we analyzed carbon and nitrogen stable isotope ratios in primary producers (mangrove leaf litter, phytoplankton and microphytobenthos), particulate organic matter, sedimentary organic matter and benthic macro-invertebrates from 3 microhabitats (tidal creeks, inside forests and forest gaps) in a mangrove forest in Trang province, Thailand. The stable isotope values of particulate and sedimentary organic matter did not differ greatly between microhabitats, and values were relatively similar to mangrove leaf litter. Invertebrates from tidal creeks and inside forests also showed delta 13C values similar to mangrove leaf litter, whereas invertebrate tissues from forest gaps were close to microphytobenthos VC values. Most invertebrates showed an enriched delta 15N value compared to the local particulate and sedimentary organic matter. These results indicate that invertebrates utilize different food sources in different microhabitats; they utilized mainly mangrove detritus in the tidal creeks and inside forests, but mainly microphytobenthos in the forest gaps. Moreover, the invertebrate biomass was highest in the forest gaps. This is important new information supporting the view that the mangrove food web is actually a diverse combination of webs based on a variety of resources, including homogenous mangrove detritus.