Do mangrove root structures function to shelter benthic macrofauna from predators?

Clarification of the role of mangrove root structures as shelter from predators for benthic animals was investigated by considering (1) the impact of predation on benthic faunal communities in a mangrove forest as indicated by a predator exclusion experiment, and (2) the uses and effects of mangrove root structures by benthic animals under laboratory conditions. In the exclusion experiment, three treatments (predator exclusion cages, partial cages and un-caged controls) were established on surface substrates in each of 3 microhabitats (tidal creek, mangrove cover present and mangrove cover absent) in a Rhizophora mangrove forest in Southern Thailand. After 1 month, benthic invertebrates were sampled and comparisons made of their species' richness, abundance and biomass among the treatments. Laboratory experiments were undertaken in tanks containing artificial mangrove roots, using 2 dominant crab species (Perisesarma indiarum and Uca bengali) as prey and the barred mudskipper Periophthalmus argentilineatus as predator. Crab preference for root structure and predation rates were recorded. Predator exclusion from the mangrove area resulted in enhanced species' richness, abundance and biomass of benthic invertebrates in all microhabitats, including those with mangrove roots. However, the partial cage treatment did not change such characteristics, indicating that the artificial cage itself did not affect the animals. The laboratory experiments demonstrated that crab preferences for root structures were not influenced by predator presence, and that root structures did not reduce crab predation rates. Such process of dominant species might be cause for significant predation in field benthic community. The overall results indicated that predation was significant for species' richness, abundance and biomass of benthic mangrove forest communities, and vertical root structures did not necessarily provide effective shelter for benthic animals.