Growth, development and condition of Dendraster excentricus (Eschscholtz) larvae reared on natural and laboratory diets

Feeding invertebrate larvae may be food limited while developing in the ocean. If they are, then their time in the plankton is prolonged, which likely increases mortality. Food limitation could be due to the quantity and/or quality of the food available. In an effort to answer how food type influences larval nutrition, we compared growth, development and lipid deposition for Dendraster excentricus larvae reared in natural seawater from two depths (1 and 20 m) and in filtered seawater on a monoculture laboratory diet of 6 cells L 1 of the green alga Dunaliella tertiolecta (Butcher). Five days post-fertilization, larvae reared on the laboratory diet had developed to the latest stage, were the largest and had lipid deposits. Larvae reared on natural surface water were intermediate in size and developmental stage, and larvae reared in the water from 20 m depth were the smallest and developed the slowest. This trend continued at 8 days post-fertilization when surface water diet larvae were similar in size to laboratory diet larvae, but their juvenile rudiments were significantly smaller. To assess food availability in each food treatment, we compared the concentration of chlorophyll (Chl) a, b and c in natural seawater from each depth and in D. tertiolecta culture in filtered seawater. Natural seawater collected from the surface had the highest concentration of Chl a and c, whereas Chl b was not significantly different between treatments. Increased Chl concentrations in the surface water are likely due to higher concentrations of diatoms and dinoflagellates, which are typically not high-quality food items for echinoid larvae. Our results support a hypothesis that echinoid larvae in the water column may be limited by food quality.