PRE-FEEDING EMBRYOS OF ANTARCTIC AND TEMPERATE ECHINODERMS USE DISSOLVED ORGANIC MATERIAL FOR GROWTH AND METABOLIC NEEDS

The energy reserves of eggs of marine invertebrates have been assumed to supply the metabolic needs of development until feeding on particles commences. This view is challenged by recent laboratory studies which show that marine invertebrate embryos of some nonarthropodan phyla are able to transport and use dissolved organic material (DOM, e.g. amino acids and fatty acids) in seawater as a source of material (energy) for metabolic needs and growth. Here we present results of experiments conducted in situ (in Antarctica and N. Pacific) and in the laboratory, which show that embryos could, in some cases, meet the metabolic costs of embryonic development and increase in organic weight (biomass) prior to being able to feed on particles. Increases in biomass of embryos of temperate species correlated with the timing of spring phytoplankton blooms. In contrast, the biomass of embryos (of temperate species) reared during periods of low primary productivity decreased, or remained constant. Phytoplankters exude DOM into seawater and these exudates are shown here to enhance embryonic growth. In most cases, there was no net use of endogenous reserves during prefeeding development; growth and energy needs were apparently met through consumption of DOM in seawater. We suggest that DOM is an important food source for embryos of soft-bodied marine invertebrates in polar and temperate oceans.