POWELL, M/L*; MORRIS, A/L; WATTS, S/A; Univ. of Alabama at Birmingham; Univ. of Alabama at Birmingham; Univ. of Alabama at Birmingham: Observations on Early Nutrition and Growth in Newly-metamorphosed Sea Urchins, Lytechinus variegatus

Research on early growth and nutrition of sea urchins has focused on the planktonic larval stages and the cues involved in their settlement and metamorphosis. Nutrition and growth of newly-metamorphosed juvenile sea urchins are not well understood. Larval stages are easily maintained on a variety of unicellular algae cultures; however, once the larvae metamorphose to juveniles they require a substrate-based diet on which to feed. We have isolated a benthic diatom of the genus Amphora (15-20 µm) that supports settlement and early growth in newly-metamorphosed juveniles (350-450 µm). Settlement is enhanced in the presence of a monoculture of the diatom. Feeding is initiated within 2 days of metamorphosis and is characterized by an uncoordinated movement of the teeth that break the diatoms loose from the substrate, allowing them to be transported into the mouth. This diatom will support high survivorship and growth during the first four weeks post-metamorphosis. The diatom will not support growth and survival after this time (ca. 1-1.5 mm diameter). We have successfully reared juvenile sea urchins past this critical size on a mixed-taxa biofilm containing green filamentous algae, red algae, diatoms, and their associated mucilage. This diet easily supports growth of juveniles to 10 mm diameter. Specific growth rates range from 8 to 10% body wet weight gain per day at this stage. Further evaluation of the composition of this diet may provide valuable insight into the nutrients required for early growth in these and other sea urchin species. This research is supported by the Mississippi-Alabama Sea Grant Consortium.