This study used an energy budget approach to record changes in the biology of the Antarctic sea urchin Sterechinus neumayeri in relation to environmental seasonality (i. e changes in chlorophyll standing stock and seawater temperature) over an unbroken two year period. Chlorophyll standing stock showed a brief but intense bloom each austral summer which contrasted with prolonged winter minima. Benthic chlorophyll standing stock, as recorded from sediment cores showed a similar cycle. Seawater temperature varied between -1.8°C and +1.2°C. Feeding activity was highly seasonal and closely correlated to chlorophyll standing stock. Feeding ceased during the austral winter of 1997 and 1998 for 6 and 4 months respectively. Metabolism, as measured by oxygen consumption and also ammonia excretion showed strong seasonality, with relatively brief 3 to 4 month periods of elevated activity in the austral summer contrasting with prolonged winter dormancy. Laboratory studies indicated that only 10-15% of the 3 fold seasonal rise in metabolism was caused directly by temperature (Q10=2.5) and that 80- 85% was related to increased physiological activity associated with feeding. Growth rate was measured over one year and was very slow. Comparison with other studies indicated that echinoid growth rate is strongly dependent on food availability, but that maximal growth rate is limited by seawater temperature, or by a co-varying factor. S. neumayeri is an annual spawner and histology was used to describe both the vitellogenic cycle and also to calculate reproductive output. Comparison with other published studies worldwide indicated that reproductive output is highly dependent on food availability, and that maximal reproductive output is not limited by temperature. Although the overall P: B ratio was low, the ratio of reproductive production to total production was higher than expected. These results indicated that due to the low metabolic rate only 12-16% of total body energy levels were used to endure the prolonged non-feeding polar winter. The overall annual growth efficiency was greater than for warmer water species, due to the larger relative contribution to reproductive output.