Seasonal Pattern of Reproduction of the Sand Crab, Emerita Analoga, in Southern California

Abstract

Reproductive activity was studied over a 20—month period in a population of the sand crab, Emerita analog, at Whale View Point in La Jolla, California, through collections made at monthly or semimonthly intervals. Marked animals were also observed in tanks containing only females, only males, and both males and females. Males over 5 mm in size were potentially fertile and were present in this population throughout the year. Oviferous females were observed in the field from February (1967) or March (1966) the beginning of September. The failure of isolated females to produce eggs, and the low frequency of oviferous females at Whale View Point in the early spring of 966, when the ratio of fertile males to potentially fertile females was very low, suggested that some stimulus by the male is necessary for egg production. Females of the largest modal size classes showed the highest average frequency of egg carrying and initiated egg production earliest in the season. Laboratory observations showed that egg masses were usually produced soon after molting, and were carried for an average of 22.5 days. Individual females produced up to four consecutive egg masses in the laboratory. In field populations, considerations of the percentage of oviferous females, the length of time eggs were carried, and the duration of the breed season, suggested that the larger females breed repeatedly if conditions are favorable. Production of egg masses in the Whale View Point population was synchronized for individuals within each modal class so that the frequency of oviferous females fluctuated cyclically during the season.