Development and expression of sexual maturity in femaleCalanus pacificus (Copepoda: Calanoida) in relation to food quality

Abstract

Dinoflagellates, which comprise an important part of the phytoplankton in the neritic region of the Southern California Bight, are known to be grazed byCalanus pacificus; rates of ingestion, development and survival of nauplii are influenced by the food quality of dinoflagellates. We have examined the effects of dinoflagellate food quality on reproduction ofC. pacificus females sampled in La Jolly Bay (32°N; 117°W) between 6 April and 4 May 1988. Four sets of experiments were conducted in which copepods were fed five different species:Gymnodinium splendens, Gyrodinium resplendens., G. dorsum, Exuviella mariae lebourae andGymnodinium simplex. These species were selected on the criterion of their success in supporting the growth of nauplii in previous rearing experiments. The experimental culture concentration was maintained at 100µg C 1−1, near that of the natural seston. As indices of successful reproduction, we measured the percentage of spawning females and the number of eggs laid per female per day. Laboratory results were compared to stages of ovarian maturation of wild females. Four stages of maturation were determined using histological and microscopic observations.Gymnodinium splendens, Exuviella mariae lebourae, andG. simplex yielded clearly inferior results: few females were able to lay eggs repetitively over the first few days of confinement.Gyrodinium resplendens and, above all,G. dorsum yielded the best results. The stage of sexual maturation in situ appears to influence the rhythmicity of egg-laying events. In the presence of high-quality food, females are able to maintain high reproductive rates by sustaining the maturation of successive batches of eggs; good food quality appears to assure this secondary vitellogenesis and the rapid turnover of ovocytes.