Fauna of the mangrovesBarnacles are actually crustaceans, which include members such as prawns and crabs. Once they find a suitable site, they attach themselves head-first to the support by secreting a strong protein cement, forming strong calcareous plates around themselves. They feed during high tide using their legs like a filtering device, sieving plankton from the water during hide tide to their mouth. When the tide recede they retreat to the safety of their shells, closing the valves to protect themselves from drying out.