Feeding and asexual reproduction of the jellyfish Sarsia gemmifera in response to resource enrichment.

Jellyfish are ubiquitous predators in marine pelagic environments and can sometimes control their zooplankton prey populations. Recent considerations of the fertilization of entire food webs in coastal areas make it important to investigate the response of jellyfish to resource enrichment. We investigated feeding, assimilation and life history parameters in the hydromedusa species Sarsia gemmifera. S. gemmifera was able to ingest up to 3 micro g carbon per hour, which corresponds to a daily carbon ingestion that exceeds the individual's body weight (carbon). Conversion of ingested carbon into tissue was less than 30%. The assimilated carbon was allocated such that approximately 65% was used for growth and the remainder for asexual reproduction. Carbon from food was allocated to asexually produced offspring within hours. The numerical response of S. gemmifera reached saturation at prey levels of 100 or more copepods per liter. Propagule quality was influenced by maternal effects: higher net production of the mothers in higher food environments resulted in higher carbon content of individual propagules. Starvation resistance of propagules was therefore positively related to food density in the maternal environment. The food concentrations which S. gemmifera normally experiences in the field are much lower than the food levels at which this species had its maximum asexual reproductive output in the laboratory. Therefore, S. gemmifera may potentially benefit from food web perturbations which increase crustacean zooplankton densities.