Biometry and trophodynamics of Salpa thompsoni foxton (Tunicata: Thaliacea) near the Antarctic Peninsula in austral summer, 1983?1984

Abstract

Salpa thompsoni aggregates have a biometric profile similar to that of mid-latitude salps, being approximately 96% water and only about 1% organic matter. Of its ash-free dry weight about 13.6% is carbon and 3.1% is nitrogen. All weight parameters were related to body length by a power function of ∼2.3. S. thompsoni was a dominant member of the zooplankton community in waters near the Antarctic Peninsula in the austral summer of 1983–1984, with biomass in mid-March ranging from 49 to 671 mgCm−2 and 9.6 to 146 mgNm−2. Three subpopulations occurred in separate regions: (1) the Bransfield Strait, (2) north of the South Shetland Islands, and (3) west of Elephant Island; these were dominated by 20, 30 and 40 mm individuals, respectively. Biomass was greatest in the Bransfield Strait and least near the South Shetland Islands. Clearance rate measurements of S. thompsoni on naturally occurring particulate matter were significantly lower than those previously reported for mid-latitude salps, a result which we attribute primarily to the effect of low habitat temperature (ca. 1°C). Direct measurements suggest that fecal production by 21 mm blastozoids is equivalent to 10.2% body carbon d−1 and 6.6% body nitrogen d−1. Grazing by S. thompsoni may have removed a majority of the daily primary production in March, but <1% in January. The comparatively low biomass of krill larvae in 1983–1984 may be attributed partially to competitive removal of food by salps, but an equally important effect may have been direct predation.