DEVELOPMENT, METAMORPHOSIS, AND SEASONAL ABUNDANCE OF EMBRYOS AND LARVAE OF THE ANTARCTIC SEA URCHIN STERECHINUS NEUMAYERI.

The development to metamorphosis of the shallow-water antarctic sea urchin, Sterechinus neumayeri, is described for the first time. Developmental stages are similar to those of closely related temperate species with feeding larvae, but the rate of development is extremely slow. Hatching of ciliated blastulae occurs approximately 140, 128, and 110 hours after fertilization at -1.8, -1.0, and -0.5°C, respectively, more than twice the time required for closely related temperate species near their normal ambient temperature. Larvae reared at -1.8 to -0.9°C are capable of feeding 20 days after fertilization and are competent to metamorphose after 115 days. Early cleavage embryos, blastulae, gastrulae, and prism larvae of this species were collected from the plankton adjacent to McMurdo Station, Antarctica, in early November and December, 1984 and 1985. Echinoplutei were not found during this study, but they have been collected from the plankton in other years; there is no evidence that the larvae are demersal. The timing of spawning ensures that feeding larvae are in the plankton during the abbreviated summer peak of phytoplankton abundance in McMurdo Sound. Recruitment of juveniles into the benthos most likely occurs in synchrony with the subsequent period of high levels of benthic chl a concentrations.