A Behavioral and Ecological Study of the Fiddler Crab UCA CRENULATA

The social interaction and behavioral activities of a population of fiddler crabs, Uca crenulatat located in the Aqua Hedianda lagoon in Carlsbad, California, is the subject of this study. Variations in environmental factors as well as seasonal behavioral changes cause an important fluctuation in the male to female ratio and in population density. A daily and seasonal variation is observed in the different behavioral activities displayed by the crab colony and are caused by biotic and abiotic environmental factors and by intrinsic hormonal changes. A male color variation from dark to light is related to behavioral changes during the breeding season. This lightening of the carapace, most likely caused by sexual hormones, is a thermoregulatory advantage for the mating male. Studies of the waving behavior of the light colored male in presence of a female, shows wave periods ranging from 1 to 5 seconds. The rate of the wave\u27s major component corresponds to the optimum stimulus speeds (30-50 degrees,/ sec.) of a rate sensitive neuron found in the optic nerve of the crabs. These results show a strong relation between behavioral data obtained on the field and physiological data concerning movement and rate selective neurons in the eye of the crab U. crenulata. The identification of 9 different stages in the egg development of U. crenulata as well as the time necessary to complete the incubation shows that the breeding cycle length is 2 weeks