5 TESTS OF FOOD-LIMITED GROWTH OF LARVAE IN COASTAL WATERS BY COMPARISONS OF RATES OF DEVELOPMENT AND FORM OF ECHINOPLUTEI

Any single method of testing food limitation can be misleading or inco nclusive. We therefore used five different tests for food-limited grow th of larvae of a sea urchin from the northwest Mediterranean: 1. In b oth spring and autumn, larvae given a nearly natural ration of food fr om daily changes of seawater grew and developed more slowly than larva e with the same water enhanced with a cultured alga. 2. Larvae given a nearly natural ration of food developed more slowly in autumn, when c oncentrations of chlorophyll a and particles in the plankton were lowe r, than in spring when these indications of food were higher. 3. Larva e given the enhanced ration grew and developed more rapidly than larva e in presumed cohorts in the plankton. 4. In both spring and autumn, l arvae in the field had a food-limited form (longer arms and delayed fo rmation of the echinus rudiment) in contrast to larvae given an enhanc ed ration. 5. Larvae in the autumn plankton had a more food-limited fo rm than larvae in the spring plankton. Results of all five tests indic ated food-limited growth in coastal waters in autumn; three indicated food-limited growth in spring. The concentrations of natural food were not unusually low. Food-limited growth suggests that these larvae may commonly feed with maximal or near-maximal clearance rates. If echino id larval growth is limited by food under these conditions, it is like ly that growth of other larval invertebrates is food limited in many c oastal waters.