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 inconclusive. We therefore used five different tests for food-limited growth of larvae of a sea urchin from the northwest Mediterranean: 1. In both spring and autumn, larvae given a nearly natural ration of food from daily changes of seawater grew and developed more slowly than larvae with the same water enhanced with a cultured alga. 2. Larvae given a nearly natural ration of food developed more slowly in autumn, when concentrations of chlorophyll a and particles in the plankton were lower, than in spring when these indications of food were higher. 3. Larvae given the enhanced ration grew and developed more rapidly than larvae in presumed cohorts in the plankton. 4. In both spring and autumn, larvae in the field had a food-limited form (longer arms and delayed formation of the echinus rudiment) in contrast to larvae given an enhanced ration. 5. Larvae in the autumn plankton had a more food-limited form than larvae in the spring plankton. Results of all five tests indicated 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 echinoid larval growth is limited by food under these conditions, it is likely that growth of other larval invertebrates is food limited in many coastal waters.