Original Paper

Polar Biology

, Volume 14, Issue 4, pp 243-251

First online:

Vertical distribution and abundance of mesoplanktonic medusae and siphonophores from the Weddell Sea, Antarctica

  • F. PagèsAffiliated withAlfred-Wegener-Institut für Polar- und Meeresforschung
  • , F. KurbjeweitAffiliated withAlfred-Wegener-Institut für Polar- und Meeresforschung

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Abstract

The composition, abundance and vertical distribution of mesoplanktonic cnidarians collected along a transect across the Weddell Sea have been analysed. The transect was characterized by a thermocline, approximately between 200 and 100 m, which deepened significantly towards the shelf edges. In total, 10 species of medusae and 18 species of siphonophores were identified. The most abundant medusae were Pantachogon scotti (up to 11,671 specimens/1,000 m3) and Arctapodema ampla (up to 960 specimens/1000 m3). The most abundant siphonophores were Muggiaea bargmannae (up to 1,172 nectophores/1,000 m3) and Dimophyes arctica (up to 230 nectophores/1,000 m3). Five assemblages of planktonic cnidarians were distinguished: (a) epipelagic species located in and above the thermocline; (b) epi- and upper mesopelagic species located in, above and just below the thermocline; (c) epi- and mesopelagic species located in and below the thermocline; (d) mesopelagic species; (e) lower mesopelagic species. Differences in the depth distribution of the various species gave rise to a clear partitioning of the mesoplanktonic cnidarian population throughout the water column. This vertical partitioning was related to the existence of a thermocline, the structure of the water column and the vertical distribution of prey.