Search

The effects of temperature on development and viability were measured at 14 levels between -2{deg}C and +3{deg}C on embryos of two asteroids (Odontaster validus and Odontaster meridionalis) and an echinoid (Sterechinus neumayeri) from Signy Island, Antarctica. Development rates were 2 to 10 times slower than those for temperate or tropical echinoderms, with times to hatching up to 240 h. Development rates for the two asteroids differed by 1.15 x, and rates for both species approximately doubled over the experimental temperature range. In O. validus, embryo viability was independent of temperature, but in O. meridionalis viability declined with increasing temperature. Development rates for S. neumayeri were little affected by temperature above +0.2{deg}C, but declined rapidly at lower temperatures. Conversely, the number of nonviable eggs was low and constant below +1.7{deg}C, but rose rapidly at higher temperatures. A window of optimal temperature, between +0.2{deg}C and +1.7{deg}C, has therefore been proposed for development time and embryo viability in this population of S. neumayeri. Spawning trials and field observations of larvae indicated that the time of gamete release and periods of larval development in S. neumayeri coincided with austral summer sea temperatures in the same window. Embryos of O. meridionalis and O. validus are released in winter, when temperatures are constantly below -1.6{deg}C. Comparison of the different strategies suggests that larval food supply and predation during planktonic phases are not the dominant ecological factors for these species.

The rates of oxygen consumption by embryos of antarctic echinoderms (Acodontaster hodgsoni, Odontaster validus, Psilaster charcoti, and Sterechinus neumayeri) were compared to the biomas (ash-free dry organic weight) of the egg of each species. These species could survive for months to years (range: 10 months to 5 years) by relying solely on the reserves present in the egg. However, certain species did not use any of the egg's reserves during early development. Embryonic stages of O. validus (a species with planktotrophic larvae) did not decrease in lipid, protein, or total biomass during the first 35 days of development. During the first 42 days of development, embryos of A. hodgsoni (a species with lecithotrophic development) used protein as an energy source. For both species lipid composed 40 to 50% of egg biomass, but was not used as an energy reserve. Larvae of O. validus have a high-affinity transport system for amino acids dissolved in seawater (K1 = 1.3 {mu}M for alanine). The rate of alanine transport from a low concentration (50 nM) could supply 32% of the larva's metabolic needs. This is a 10-fold higher input to metabolism than was determined (3% at 50 nM) for larvae of a temperate asteroid, Asterina miniata. Larvae of antarctic echinoderms live in an environment where the food supply is low for most of the year. Relative to their metabolic rates, antarctic larvae have larger energy stores and planktotrophic larvae have higher nutrient transport capacities when compared to larvae from temperate regions. These physiological differences allow antarctic larvae to survive for long periods without particulate food.

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...