The potential for ontogenetic vertical migration by larvae of bathyalechinoderms

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 in vestigating 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.