Competition and interaction between Neosarmatium smithi (Crustacea : Grapsidae) and Terebralia palustris (Mollusca : Gastropoda) in a Kenyan mangrove

In a Kenyan mangrove, we studied the interactions between the gastropod Ter ebralia palustris and the crab Neosarmatium smithi when foraging on decayin g mangrove leaves. Interactions are considerable on account of their wide o verlap in zonation (Rhizophora mucronata belt), food items (mangrove leaves ) and activity window (diurnal low water). The snails find a leaf by a syst ematic transecting of the platform and eat the leaf after crawling on to it , usually en masse. The crabs rarely venture beyond 80 cm from their burrow s, and once they find a leaf they quickly drag it back into their burrow, p robably to reduce the strong intra-specific competition. A crab is able to drag a leaf away even if a number of snails are already feeding on it, by s trongly pulling the leaf away or by pushing the snails off the leaf. The su ccess of the "thief" depends on both the crab's size and the number of snai ls on the leaf.