Macroplankton/micronekton dynamics in the vicinity of the Prince Edward Islands (Southern Ocean) |
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Authors: | E A Pakhomov P W Froneman |
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Institution: | (1) Southern Ocean Group, Department of Zoology and Entomology, Rhodes University, P.O. Box 94, Grahamstown 6140, South Africa Fax: 0027(0)46 622 4377; e-mail: zoep@warthog.ru.ac.za, ZA |
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Abstract: | Combined trawling (rectangular midwater trawl, RMT-8 net) and acoustic (120 kHz) surveys in the upstream and downstream region
of the Prince Edward Islands were undertaken during April and May 1996 and 1997. A total of 49 species of macroplankton and
micronekton were encountered within the region investigated. Mesopelagic fishes, euphausiids, chaetognaths and tunicates dominated
numerically and by biomass. Average abundance and biomass of macroplankton/micronekton in the top 300 m layer were low, 18
individuals 1000 m−3 and 288 mg dry wt 1000 m−3, respectively. Numerical analysis revealed the presence of two major groups of stations broadly corresponding to the offshore
(upstream and downstream) and inshore (inter-island) realms. Planktonic samples and acoustic measurements revealed that elevated
densities of macroplankton/micronekton were associated with the subantarctic front region and in close proximity to the island
plateau. Based on trawling and acoustic survey results, it is suggested that large plankton and micronekton are mostly washed
around rather than across the inter-island shelf region. This is in contrast with the “replenishing hypothesis” previously
proposed for this region by other investigators.
Received: 11 May 1998 / Accepted: 25 March 1999 |
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