Egg-hatching Rhythms in Three Species of Fiddler Crabs

Abstract

The time of egg hatching of the fiddler crabs, Uca pugnax, U. pugilator and U. minax was monitored under controlled laboratory conditions and under natural field conditions. Hatch profiles were constructed by counting zoeae collected from individual females under controlled laboratory conditions every 10 minutes. Complete hatching of the 1,500–94,000 embryos in an egg sponge occurred over the course of several minutes, related to the time of the nocturnal high tide. The female aided hatching by vigorous abdominal contractions. Sampling in a typical intertidal creek every two hours at four depths over a 33-hour period indicated a large peak of zoeae near the nighttime high tide. Such timing may minimize predation on eggladen females walking to the water's edge to deposit their hatching zoeae. Tidal timing may also reduce predation as well as tidal flushing of Uca larvae.