THE POTENTIAL FOR ONTOGENIC VERTICAL MIGRATION BY LARVAE OF BATHYAL ECHINODERMS

Planktotrophy is a relatively common developmental mode among bathyal and abyssal echinoderms, but the sources of food used by deep-sea plan ktotrophic larvae remain generally unknown. Very few deep-sea echinode rm larvae have been collected in plankton samples, so we do not know w hether larvae migrate to the euphotic zone to feed or if they rely on bacteria or detritus at greater depths. We approached this question in directly by investigating whether larvae of bathyal echinoids can tole rate the temperatures they would encounter in the euphotic zone and wh ether they possess sufficient energy stores to migrate to the euphotic zone without feeding. Twenty-four hour survival at 20 and 24 degrees C was always much lower than survival at colder temperatures, but ther e were species-specific and stage-specific differences in temperature tolerances. A numerical model of the energy consumed by migrating larv ae predicted that larvae should be able to reach adequate phytoplankto n concentrations before exhausting parental reserves, unless they swim very slowly and have very high metabolic rates. These results suggest that long vertical migrations are more likely to be limited by physio logical tolerances than by energy stores.