Seasonality of feeding and nutritional status during the austral winter inthe Antarctic sea urchin Sterechinus neumayeri

The seasonal pattern of food intake and tissue energy status was measured o ver a 2 year period for two populations of the common Antarctic echinoid St erechinus neumayeri living on contrasting substrata at Rothera Point, Adela ide Island, Antarctica. Food intake was estimated from faecal egestion, and both tissue mass and energy content assessed. Food availability was intens ely seasonal, in that water column chlorophyll content and sediment pigment content varied markedly throughout the year. In response, both urchin popu lations showed an extremely seasonal cycle of faecal egestion, indicating a strong seasonality of feeding activity. Urchins from North Cove living on soft sediment fed at a considerably higher rate, and had a significantly la rger Aristotle's lantern, than those in South Cove, I km away, living on ha rd substrata and taking a more cosmopolitan diet. Faecal egestion in both p opulations was zero for a 7 month period in the austral winter of 1997, and again for a 4 month period in 1998. During the austral summer of 1997/1998 , 84% of the total annual energy intake took place in the period January to March. Significant decrease in gut tissue mass provided energy for mainten ance in early winter, although progressive reduction of both gonad energy c ontent (but without a detectable change in gonad mass) and body wall organi c mass provided energy during the late winter period. The mass of reproduct ive tissue showed large differences between the two sites, but there was no marked decrease associated with spawning. Tissue proximate composition was assessed stoichiometrically from elemental composition and also checked by direct assay; gonad tissue was richer in lipid than gut tissue, though bot h were dominated by protein and contained only small amounts of carbohydrat e. These data suggest that the very strong seasonality of food intake does not pose a significant energetic challenge for this species.