FEEDING BEHAVIOR AND REPRODUCTIVE CYCLES IN PISASTER OCHRACEUS

Abstract

Pisaster ochraceus shows a definite seasonal feeding periodicity, in terms of per cent of the population feeding at one time, dry weight ingested, and in composition of ingested prey. Less than 5% are feeding in Jan. and Feb.; 60% to 80% in July and Aug. The dry weight ingested varies from about 3 g/ tidal cycle/100 animals in the winter to about 30 g in the summer months. Chitons are the principal winter prey, while barnacles and limpets are fed on most often in the summer. Cyclic changes in gonad and pyloric caeca size and histological appearance characterize this species. The gonads are smallest in the fall, and grow during the winter to a maximum in the late spring, when spawning occurs. The pyloric caeca size-changes are approximately inverse to those of the gonads. Seasonal histological changes of the oocytes, and storage granules in the pyloric caeca, are correlated with the gross organ patterns. Two factors are suggested as explanations for these cyclic phenomena more favorable summer feeding for both the adult and larval Pisaster may have led to evolution of a storage function for the pyloric caeca; nutrients could then be transferred to the gonads in the winter; and it would seem evolutionarily advantageous to fill more of the limited space available in the arms with gonads than with pyloric caeca in the spring, at the time of spawning.