Mesoscale zooplankton distribution patterns and euphausiid population ecology in the south-west Atlantic

• Main Author: Tarling, Geraint Andrew
• Format: Thesis
• Language: English
• Published: 1995
• Subjects: Antarctic; Austral; Antarc*
• Online Access: https://eprints.soton.ac.uk/353530/; https://eprints.soton.ac.uk/353530/1/96057098.pdf

Two mesoscale net sampling surveys were conducted in the south-west Atlantic between 34° and 55 °S. The first survey was in the austral spring of 1990 and used both an RMT8 net which was trawled obliquely down to 200 or 300 m and caught mainly macrozooplankton and a Bongo net which was deployed at the surface and sampled mesozooplankton. The second survey was in the austral spring of 1991 and used a Bongo net which was deployed obliquely down to 50 m and sampled mesozooplankton. This thesis considers the species composition and abundance of these samples and represents one of the first insights into the mesoscale biogeography of zooplankton communities in the south-west Atlantic. 155 species from 9 taxonomic groups were considered including euphausiids, hyperiid amphipods, chaetognaths, salps, siphonophores, and nektonic/planktonic fish. Multivariate analyses were used to highlight species assemblage distribution patterns and determine strongly correlated environmental variables. In the 1990 RMT8 samples, species assemblages showed a distribution pattern related to the location of water masses, which was reflected in a combination of water mass and latitude being the most strongly correlated environmental variables. In the 1990 Bongo samples, a combination of seasurface temperature and latitude were most strongly correlated environmental variables and different species assemblages showed a pattern of being located in exclusive temperature ranges. The two sample sets did exhibit some common distribution patterns especially in the warm, sub-tropical waters to the north and the Falkland Shelf to the south. However, there were fundamental differences in the mid-latitudes regions, possibly reflecting the reduced ability of larvae to counteract expatriating forces when compared with adults. Further comparisons made between the 1990 and 1991 Bongo sample sets highlighted some of the causal factors behind distribution patterns. For instance, the precise definition of the boundary between sub-tropical and sub-Antarctic ...