Metabolism of gymnosomatous pteropods in waters of the western Antarctic Peninsula shelf during austral fall

Two species of Southern Ocean gymnosomatous pteropods with dissimilar distribu- tional ranges were collected from western Antarctic Peninsula (WAP) shelf waters in the vicinity of Anvers, Lavoisier, Adelaide and Charcot Islands from March to April 2010 and between 0 and 500 m. The sub-Antarctic gymnosome species, Spongiobranchaea australis, typically occupies regions north of the Polar Front, whereas the true Antarctic gymnosome species, Clione antarc- tica, inhabits colder waters and higher latitudes. Oxygen consumption rates, ammonia excretion rates, proximate body compositions and the activities of 3 metabolic enzymes — lactate dehydro- genase, malate dehydrogenase, and citrate synthase (CS) — were determined in both gymnosome species. Oxygen consumption rates of S. australis and C. antarctica were found to be similar; how- ever, the mean ratio of oxygen consumed to ammonia excreted (O:N, 61.26 ± 18.68:1) indicated that S. australis was oxidizing primarily lipids while C. antarctica was oxidizing a mixture of proteins and lipids (26.41 ± 14.82:1). Proximate body compositions based on percent protein, per- cent lipid, and carbon to nitrogen ratios, suggested larger lipid storage in C. antarctica (~5%) than in S. australis (~3%). CS activities among gymnosomes were dissimilar, and comparisons of enzyme activities were made to other Antarctic organisms. Observed differences in S. australisu0027 physiological indicators may be related to prolonged starvation, whereas C. antarctica appears ready to survive overwintering in Antarctica. Water mass advection from the Antarctic Circum - polar Current is thought to be transporting S. australis onto the WAP shelf, and away from its typical sub-Antarctic habitat.