Effects of food concentration and availability on the incidence of cloningin planktotrophic larvae of the sea star Pisaster ochraceus

A decade ago, cloning was first observed in the planktotrophic larvae of se a stars obtained from plankton tows. However, no controlled experimental st udies have investigated what factors may regulate this remarkable phenomeno n. In the present study we offer the first documentation of cloning in the planktotrophic larvae of Pisaster ochraceus from the northern Pacific coast . This species was used as a model system to investigate three factors that may influence the incidence of asexual reproduction (cloning) in planktotr ophic sea star larvae. In an initial experiment, larvae were reared under n ine combinations of three temperatures and three food (phytoplankton) conce ntrations. Larvae reared at 12-15 degreesC and fed the highest food concent rations grew larger than the other larvae and produced significantly more c lones. In a second experiment, qualitatively different algal diets were fed to larvae reared under the conditions found to be optimal in the initial e xperiment. Up to 24% of the larvae consuming a mixed phytoplankton diet of Isochrysis galbana, Chaetocerous calcitrans, and Dunaliella tertiolecta clo ned, and significantly more clones were produced by these larvae than by th ose fed monospecific diets. Our experiments indicate that cloning generally occurs after larvae have attained asymptotic body length and only when foo d is abundant and of high quality. Since larval mortality is considered to be extremely high for marine invertebrates with planktotrophic larvae, prod uction of clones under optimal conditions of temperature and food may serve to increase larval populations when the environment is most conducive to l arval growth.