Behavioral basis of internal-wave-induced shoreward transport of megalopae of the crab Pachygrapsus crassipes

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Abstract
In field experiments, megalopae of the intertidal crab P. crasasipes Randall, released in the water column at 1-5 m depths and observed by a SCUBA diver, swam to the surface. Laboratory experiments on the orientation of megalopae demonstrated a positive phototaxis at 3 light intensities (1240, 690, 70 lx), negative geotaxis, high baro- and photokinesis, and a strong tendency to cling to objects in the water. Spontaneous swimming of megalopae yielded an average speed of 9.5 cm s-1. These observations are consisted with the hypothesis that P. crassipes megalopae inhabit the neuston and are transported shoreward by tidally forced internal waves.