Macro- and megaplanktonic cnidarians collected in the eastern part of the Weddel Gyre during summer 1979

22 pagesThe species composition, abundance and spatial distribution of macroplanktonic cnidarians in the eastern part of the Weddell Gyre are described from a series of nekton samples collected over three depth ranges between 0 and 2000 m. On average, cnidarians contributed 52·6% to the biovolume of these samples, although the range was high (5·0–93·1%). In total 23 species of siphonophores and 20 species of medusae were identified; a number that is very high in comparison with previous studies. There was a high diversity at bathypelagic depths, with 38 species being collected below 1000 m. The most abundant siphonophores were Dimophyes arctica (up to 45 nectophores per 104 m3) and Heteropyramis crystallina (up to 22 nectophores per 104 m3). The most abundant medusa was Pantachogon haeckeli (up to 30 specimens per 104 m3). Medusae were most abundant at mesopelagic depths, reaching 46 specimens per 104 m3 in the 500–1000 m depth range. Smaller calycophoran siphonophores were concentrated in the top 500 m of the water column, with total numbers averaging 107 per 104 m3. The number of larger calycophorans in-creased with depth, being most abundant in the 1000–2000 m depth range. Although many species had a widespread geographical distribution within the sampling area, the hydrographical conditions appeared to be affecting the distribution of som