ZIEGLER, T. A.; FORWARD, JR., R. B.; Duke University Marine Laboratory; Duke University Marine Laboratory: Synchronous timing of larval release in the mole crab, Emerita talpoidia

Ovigerous females of the mole crab Emerita talpodia were monitored in the laboratory to determine if the time of larval release is synchronous and to investigate the role of the female in this synchrony. To determine the time of larval release, ovigerous females were placed under a 14:10 LD cycle simulating the ambient photoperiod. Hatching was synchronous and occurred shortly after the onset of darkness as a short burst lasting approximately 5-15 min. An individual mole crab will release batches of larvae for up to three successive nights, suggesting that the larval release rhythm is under endogenous control. Crabs monitored under constant low-level red light displayed the same release pattern, with hatching occurring near the time of expected sunset, indicating a circadian rhythm in larval release. The female may control the timing of larval release by rapidly beats her walking legs and pleopods, presumably to assist in breaking the egg case membrane. A portion of the egg mass (50-300 embryos) was separated from the female, and the time of hatching of the detached embryos was compared with those still attached to the female. Embryos were removed �48 h before the predicted time of larval release and observed for three days after the embryos attached to the female hatched. The detached embryos failed to hatch during the observation period, suggesting that mechanical stimuli from the female is important in the hatching process.