A FIELD STUDY OF GROWTH AND REPRODUCTION IN APLYSIA CALIFORNICA

Abstract

Observations of field growth rates, reproductive activities and abundance of A. californica were made over 3 yr on Santa Catalina Island off southern California [USA]. The mean wt of the population varied with the location in which the animals were collected, presumably as a result of differing food availability. Seasonal wt differences were also apparent. Small specimens of A. californica appear between Feb. and May. Mean wt reached a maximum between June and Aug. Considerable variability was encountered from year to year. Tagging and recapture showed that growth reached a maximum in the spring just prior to breeding. The rate decreased thereafter until wt loss was experienced in Aug. and Sept. A. californica was usually most abundant in the spring, with numbers decreasing during the summer. The animals almost completely disappeared during the months of Oct., Nov. and Dec. with the exception of extremely small specimens found on algae. Breeding activity was occasionally observed as early as April and reached its greatest intensity during July and Aug. when at least 80% of the animals collected were in breeding aggregations. Histological examination of gonads showed maximum oocyte diameter between June and Oct. and minimum between Jan. and March. Data are consistent with an annual species whose extended summer breeding period is terminated by the death of mature individuals during the fall.