CHEMICAL-COMPOSITION OF ANTARCTIC ZOOPLANKTON DURING AUSTRAL FALL ANDWINTER

Water level, ash content, proximate (protein, lipid, carbohydrate and chitin) and elemental (carbon and nitrogen) composition were analyzed in twenty-three species of Antarctic zooplankton collected during the austral fall (1986) and winter (1988) from the Scotia/Weddell Sea regi on. Extremes in water level, ash content and organic components were t ypified by copepods and gelatinous forms. Ostracods and polychaetes we re generally similar in composition to copepods, being only slightly h igher in water level and ash content. Chaetognaths exhibited a composi tion intermediate in character with some components similar in value t o that shown by crustaceans (i.e. protein) while other components were more in the range of values seen in gelatinous forms (i.e. water leve l and ash content). Protein was the major proximate component and meas ured values (as % AFDW) were fairly uniform among non-gelatinous speci es (x = 33.9 +/- 6.9). Lipid levels were variable, with high values (> 30% AFDW) only found for the copepods Calanoides acutus, Calanus prop inquus and Euchaeta antarctica. Carbohydrate values were low in all sp ecies examined. Chitin was measured in crustacean species only. With t he exception of C. acutus (x = 2.5% AFDW chitin), values were similar among species with mean values being slightly higher in fall (x = 11.8 +/- 2.5) than in winter (x = 6.7 +/- 1.8). Among non-gelatinous speci es, the ratio of carbon to nitrogen was positively correlated with the lipid to protein ratio, underscoring the compositional association be tween elemental and proximate components in these groups. In gelatinou s species, the relationship between carbon:nitrogen and lipid:protein was inconsistent and less pronounced. Caloric content was estimated fr om recovered organic matter for nongelatinous species, As a function o f wet weight and dry weight, values reflected differences in water lev el and ash content among individual species. As a function of ash-free dry weight, values were similar among all species (x = 3.6 +/- 0.9 kc al/g). Seasonal comparisons were possible for 12 of the 23 species. Am ong crustaceans, changes in water level and organic components were va riable reflecting dissimilar trophic, reproductive or ecological habit s among different species. Essentially no change in composition betwee n fall and winter was observed for diapause species (e.g. Calanoides a cutus and Rhincalanus gigas) as well as for omnivorous/carnivorous spe cies (e.g. Gaetanus tenuispinus). Conversely, large compositional chan ges were evident for Calanus propinquus, a small-particle grazer that relies heavily on lipid reserves. Chaetognaths and some gelatinous spe cies exhibited a considerable decrease in ash content from fall to win ter which, for most cases, was mirrored by some degree of increase in lipid level. At present, however, scant data are available to help exp lain the observed patterns of compositional change within non-crustace an species.