The Potential for Ontogenetic 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 planktotrophic larvae remain generally unknown. Very few deep-sea echinoderm larvae have been collected in plankton samples, so we do not know whether larvae migrate to the euphotic zone to feed or if they rely on bacteria or detritus at greater depths. We approached this question indirectly by investigating whether larvae of bathyal echinoids can tolerate the temperatures they would encounter in the euphotic zone and whether they possess sufficient energy stores to migrate to the euphotic zone without feeding. Twenty-four hour survival at 20 and 24 °C was always much lower than survival at colder temperatures, but there were species-specific and stage-specific differences in temperature tolerances. A numerical model of the energy consumed by migrating larvae predicted that larvae should be able to reach adequate phytoplankton 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 physiological tolerances than by energy stores