Rapid development of megalopae of the fiddler crab ilea pugilator reared over sediment: implications for models of larval recruitment

Fiddler crabs l ~v e as adults in estuaries but their planktonic larvae develop in the coastal ocean. Megalopae, the flnal larval stage, may return to adult habitats either slowly, via transport by residual currents near the bottom, or rapidly, by riding nocturnal flood tides. When reared in the laboratory over sedlment from adult habitat, megalopae of the fiddler crab Uca pugilator molted to the crab stage in 7.5 1 1.64 d at 22 to 24OC and in 4 . 3 t 2.66d at 28C. The rate of development over sediment is 2 to 3 times faster than rates observed when megalopae are reared in clean containers. On their second day of development, megalopae in a settlement tank remalned on sediment exposed during artificial low tides and some molted to crabs a day later In clean containers, survival of megalopae and their competence to metamorphose declined with time while the occurrence of aberrant behavior increased. These results, together with what is known about the distribution and behavior of megalopae in coastal waters, are consistent with a mechanism of immigration into estuaries based on rapid transport of megalopae by tidal currents.