A FIELD STUDY OF GROWTH AND REPRODUCTION IN APLYSIA CALIFORNICA

1. Observations of field growth rates, reproductive activities, and abundance of Aplysia calfiornica were made over a three-year period on Santa Catalina Island off southern California. 2. The mean weight of the population was found to vary with the location in which the animals were collected, presumably as a result of differing availability of food. 3. Seasonal weight differences were also apparent. In general, small specimens of A. californica appear between February and May. Mean weight reached a maximum between June and August. Considerable variability was encountered from year to year. 4. Tagging and recapture showed that growth rates reached a maximum in the spring just prior to breeding. The rate decreased thereafter until weight loss was experienced in August and September. 5. A. californica was usually most abundant in the spring, with numbers decreasing during the summer. The animals almost completely disappeared during the months of October, November, and December with the exception of extremely small specimens found on algae. 6. Breeding activity was occasionally observed as early as April and reached its greatest intensity during July and August when at least 80% of the animals collected were in breeding aggregations. 7. Histological examination of gonads showed maximum oocyte diameter between June and October, and minimum between January and March. 8. Data are consistent with an annual species whose extended summer breeding period is terminated by the death of mature individuals during the fall.