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1. The common Antarctic echinoid Sterechinus neumayeri (Meissner) feeds mostly on diatoms, although such things as seal feces are also used for food when available.2. Specimens of S. neumayeri in McMurdo Sound have discrete reproductive periodicities as do most echinoids in other parts of the world. Oocyte growth begins in the summer between November and May, the oocytes take from 18 to 24 months to reach maturity after beginning growth, and spawning occurs sometime in the winter or spring between May and December. The embryos presumably develop slowly into demersal echinopluteus larvae in the summer when plant food is available.3. Nutrients seem to be accumulated in the nutritive phagocytes of the gonads during the summer when phytoproduction occurs, and the gonads increase in size during this period. These nutrients are probably utilized during the winter to maintain a relatively constant rate of gametogenesis.4. The lipid, carbohydrate, protein and total nitrogen levels in the gonads, test, gut and gut...

Studies of the benthos between 30 and 60 m at Cape Armitage, McMurdo Sound. Antarctica, reveal an epifaunal community in which sponges and their asteroid and nudibranch predators predominate. Field experiments demonstrated that, with the exception of Mycale accrata, the growth rates of the sponges are too slow to measure in one year. Mycale, however, was observed to increase its mass as much as 67%. Because of its more rapid growth rate, Mycale appears to be the potential dominant in competition for substratum space, the resource potentially limiting to the sessile species. This conclusion is supported by observations of Mycale growing over and, in some cases, apparently having smothered many other sessile species representing at least three phyla. The densities and size frequency distributions of all the predators were measured; numerous feeding observations allowed an accurate appraisal of dietary compositions. Because of the predators' very slow consumption rates, however, direct measures of ingestion and its impact on prey populations were not possible. Estimates of the ingestion rates were derived from measurements of predator respiration rates, growth rates, and gonad growth. Data from the field surveys and the energetics studies suggest that Mycale is prevented from dominating the space resource by the predation of two asteroids. Perknaster fuscus antarcticus and Acodontaster conspicuus. Adult Perknaster specialize on Mycale, and the sponge provides a small proportion of the diet of A. conspicuus. Acodontaster conspicuus and the dorid nudibranch Austrodoris memurdensis are the most important predators on three species of rossellid sponges (Rossella racovitzae, R. nuda, and Scolymastra joubini). Despite this relatively heavy consumption and despite the fact that none of these sponges has a refuge in growth from potential mortality from A. conspicuus, very large standing crops of the rossellid sponges have accumulated. This accumulation appears to result from predation on larval and young A. conspicuus and Austrodoris by Odontaster validus, which is primarily a detrital feeder and apparently acts as a filter against the settlement and survival of the A. conspicuus and Austrodoris larvae. In addition, predation upon adult A. conspicuus by O. validus and the actinian urticinopsis antarcticus annually kills approximately 3.5% of the A. conspicuus population. This mortality exceeds the apparent rate at which A. conspicuus escape the larval filter.

The early development of Odontaster validus at McMurdo Sound, Antarctica, is indirect and includes equal cleavage, a convoluted blastula, a free-swimming coeloblastula, a gastrula, and a feeding bipinnaria larva. Development differs from that of other asteroids in two respects: (1) The developmental rate is extremely slow; blastulae form nearly 2 days after fertilization, gastrulation begins after 7 days, and the bipinnaria develops in about 40 to 55 days. The slow developmental rate appears to be only partly related to the low environmental temperature (-1.5°C). (2) The embryos and larvae are largely demersal. Such behavior may be an adaptation to keep the larvae out of antarctic surface waters, as does brooding in many other polar echinoderms.

Toxicity in sponges and holothurians is inversely related to latitude and may reach 100 percent for holothurians in high-diversity coral reefs. Evidence from approximately 700 experiments and from underwater observations suggests that predation by fish has resulted in natural selection for noxious and toxic chemical compounds in species within these taxa.

The mean oxygen consumption, QO2, in µlO2/g/hr at -1.8° C (ambient temperature), of the antarctic echinoid Sterechinus neumayeri and the antarctic asteroid Odontaster validus, determined with an oxygen electrode, were recorded as follows: neumayeri (whole body) 3.5±2.1, (body wall) 5.6±0.9; and O. validus (whole body) 4.9±1.5, (body wall) 9.6±2.0. The oxygen consumption fell with the decline in partial pressure of oxygen as the oxygen was used by the organisms. Small increases in temperature, from -1.8° C to 3° C, had no significant effect on the QO2 of whole animals, and at 3° C only a small effect on the QO2 of the body wall. Comparisons indicate that some temperate species have QO2 values in the same range as the antarctic species. Tropical species cited, however, consume oxygen at a higher rate than the antarctic species.

The fact that samples of Odontaster validus from the Balleny Islands (67 degrees S) and Robertson Bay (71 degrees S) closely resembled reproductively samples taken from McMurdo Sound (77 degrees S) indicates reproductive synchrony in this species over much or all of their circumcontinental antarctic distribution. This synchrony suggests that the reproductive periodicities of O. validus are both adapted to and synchronized by the summer period of phytoproduction and that neither light nor temperature changes have any direct synchronizing role.

ASTEROIDS are usually considered to have little or no control over the volume of water in the perivisceral coelom, the body wall being freely permeable to water and most ions1. The Antarctic asteroid Odontaster validus Koehler, however, apparently regulates coelomic water volume to the extent of maintaining seasonal fluctuations2. This species is a “cushion” type asteroid with small, loosely scattered ossicles in a thin body wall permitting considerable flexibility in body shape. Individuals often markedly swollen with coelomic water were collected, while others were “normal” or even shrivelled. Many animals lost weight during successive weighings, and in some cases the decrease was more than 40 per cent of the original wet weight. Other animals maintained their original weight, or gained up to 30 per cent of their original wet weight, during successive weighings. Animals in the field had significantly less coelomic water in March and April, and significantly more in June, than at other times during the year. This seasonal fluctuation did not correlate with fluctuations in gonadal, pyloric caecal or intestinal caecal size. Several experiments, carried out at McMurdo Station, Antarctica, and showing other possible aspects of coelomic water volume regulation in O. validus, are described here.