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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.

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Planktotrophic larvae that occur beneath the annual sea ice in the Antarctic assimilate organic solutes and preferentially ingest bacteria, whereas they actively exclude phytoplankton. In regions where phytoplankton biomass is temporally limited by light or nutrient concentrations, the growth and development of planktotrophic larvae may not be directly coupled to phytoplankton production.

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The mode of development was ascertained for 14 of the 16 species of sea stars known to occur in shallow waters of McMurdo Sound, Antarctica (77°51'S; 166°40'E). The species were collected between September 1984 and December 1985. Females of three species, Odontaster validus, O. meridionalis and Porania antarctica, spawn small to moderate eggs (0.17 to 0.55 mm), have a high fecundity, and produce feeding larvae. Females of an undescribed Porania species spawn a few eggs (150 to 310) that are 0.55 mm in diameter and develop into demersal non-feeding larvae. Females of Diplasterias brucei and Notasterias armata produce a few (<300) large eggs (2.8 to 3.5 mm) and brood their young. Females of the remaining eight species have moderate fecundity and produce pelagic non-feeding larvae, as determined from egg type (buoyant, 0.54 to 1.28 mm diam) and direct observations of spawning and development. The high incidence (11 out of 14 species; 79%) of non-feeding development is consistent with predictions that environmental conditions in high-latitude regions are unfavorable for planktotrophic development. Nonetheless, most of the species surveyed (11 out of 14) had pelagic larvae, which contradicts inferences of unusual selection for benthic development in the Antarctic.

SYNOPSIS. Every spring for the past two decades, depletion of stratospheric ozone has caused increases in ultraviolet B radiation (UVB, 280-320 nm) reaching Antarctic terrestrial and aquatic habitats. Research efforts to evaluate the impact of this phenomenon have focused on phytoplankton under the assumption that ecosystem effects will most likely originate through reductions in primary productivity; however, phytoplankton do not represent the only significant component in ecosystem response to elevated UVB. Antarctic bacterioplankton are adversely affected by UVB exposure; and invertebrates and fish, particularly early developmental stages that reside in the plankton, are sensitive to UVB. There is little information available on UV responses of larger Antarctic marine animals (e.g., birds, seals and whales). Understanding the balance between direct biological damage and species-specific potentials for UV tolerance (protection and recovery) relative to trophic dynamics and biogeochemical cycling is a crucial factor in evaluating the overall impact of ozone depletion. After more than a decade of research, much information has been gathered about UV-photobiology in Antarctica; however, a definitive quantitative assessment of the effect of ozone depletion on the Antarctic ecosystem still eludes us. It is only obvious that ozone depletion has not had a catastrophic effect in the Antarctic region. The long-term consequences of possible subtle shifts in species composition and trophic interactions are still uncertain.

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