STRATHMANN, R. R. *; HYSERT, A. ; FOLEY, R.; University of Washington, Friday Harbor: Food Limited Growth, Plasticity in Loss and Gain of Metamorphic Competence, and Recruitment of the Cyphonautes Larva of a Bryozoan

The cyphonautes larvae of bryozoans have a low capacity for clearing food from suspension. As predicted, they starved at concentrations of food that supported growth of sea urchin larvae. Nevertheless, these bryozoans developed from egg through metamorphosis in 4 weeks at 14�C when food was abundant in laboratory cultures. The cyphonautes larvae also tolerated extended starvation at low concentrations of food. The internal sac (a rudiment of postlarval juvenile structures) shrank in starved larvae, which lost competence for metamorphosis, but the larvae regrew the internal sac and regained competence when fed. Thus the larvae can use the juvenile rudiment as a nutrient reserve when food is scarce and grow it back when food is abundant. The four week planktonic period in laboratory culture was close to the time lag between larval abundance and zooid density in P. Yoshioka�s study of a population off southern California, but a similar time lag did not occur in the population near the Friday Harbor Laboratories. Peak densities of reproductive adults occurred in the summer, larval abundance declined to low densities of precompetent larvae during the autumn and winter, then abundant competent larvae appeared from an unknown source and settled at high densities in the spring. Extreme plasticity in size and age of reproduction was confirmed: first reproduction occurred a month after settlement in colonies with only about 20 zooids when space for growth was limited.