Abundance of gelatinous carnivores in the nekton community of the Antarctic Polar Frontal Zone in summer 1994

Abstract

The species composition, abundance, vertical distribution, biovolume and carbon content of gelatinous nekton in the Antarctic Polar Frontal Zone are described from a series of RMT25 hauls collected from a series of 200 m depth layers between 0 and 1000 m. In total, 13 species of medusa, 6 species of siphonophore, 3 species of ctenophore and 1 species of salp and nemertean were identified. On average gelatinous organisms contributed 69.3% to the biovolume and 30.3% to the carbon content of the samples, although the ranges were high (0 to 98.9% and 0 to 62.6% respectively). The most important contributor to the biovolume and carbon content was the scyphomedusan Periphylla periphylla. Some specific associations and restricted vertical distributions were related to trophic interactions among ostracods, amphipods and cnidarians. Observations made near South Georgia showed that medusae and ctenophores were preyed upon by albatrosses and notothenioid fish respectively. The results support the premise that gelatinous organisms are a major and, at times, are the main component of the oceanic macroplankton/nekton community in the Southern Ocean.