Entrainment of the larval release rhythm of the crab Rhithropanopeus harrisii (Brachyura: Xanthidae) by cycles in salinity change

Ovigerous females of the crab Rhithropanopeus harrisii (Gould) were collected from an estuary having irregular tides and exposed to only a semi-diurnal tidal cycle in salinity change in the laboratory. A circatidal rhythm developed, in which larval release occurred around the predicted time of highest salinity (high tide). Thus, salinity cycles can entrain a tidal rhythm. After exposure to only a diel light/dark (LD) cycle, releases occurred mainly in the first 2 h of the dark phase. When exposed to both a tidal salinity cycle and an LD cycle, larval release depended upon the time of nocturnal high tide. Crabs only released at night. If high tide was near the beginning or within about 3 h of the end of the dark phase, releases occurred at the beginning of the dark phase. As high tide moved toward the middle of the night, an increasing proportion of crabs released around the predicted time of high tide. These data support the suggestions that (1) the LD and tidal salinity cycles control the specific time of hatching and (2) there is a hierarchy in the functional advantages for the timing of larval release, in which reduced vulnerability to visual predators is more important than avoidance of stressful salinities or intial seaward transport. © 1986 Springer-Verlag.

Duke Scholars

Author Richard B. Forward Marine Science and Conservation