Variation of storage lipid quantity with body size and season in fifth copepodites of Calanus finmarchicus from Georges Bank and the Gulf of Maine

C. B. Miller, J. Crain and C. Morgan

Oil sac volume has been estimated in live fifth copepodites (C5) of Calanus finmarchicus using video images of the side view. Careful attention has been paid to details of the approximate volume integration, and a new method is proposed. The upper limit of stored wax volume increases with body size both absolutely and as a fraction of prosome volume, because relatively more space is available for wax in large (2.8 mm prosome) than in small (1.6 mm prosome) C5. Actual amounts stored vary from the maximum for the body size to near zero from January through June at all depths and all sites in the vicinity of Georges Bank. Nevertheless there are trends. January specimens mostly retain less oil than June specimens, presumably due to some use over the summer-autumn diapause. Reduction is more advanced in February for the few C5 remaining. During April, as the winter spring generation (G1) completes development, C5 of all degrees of relative fullness are present. More are near the maximum in May and June. After factoring out body size, most C5 collected at depth during spring and early summer hold more wax than most of those collected near the surface. Patterns of data density on plots of oil sac volume versus prosome size do not, however, always shift with season and depth in a simple, readily interpreted manner.