Abstract
Mesozooplankton were sampled at shelf and oceanic stations close to South Georgia, South Atlantic during austral autumn 2004 with a Longhurst Hardy Plankton Recorder. Onshelf biomass ranged from 2.18 to 5.75 g DM m−2 (0–200 m) and was dominated by the small euphausiid Thysanöessa spp. At the oceanic stations (10.57–14.71 g DM m−2, 0–1,000 m) large calanoids, principally Rhincalanus gigas comprised ∼47–52% of biomass. Here Calanus simillimus was still active and reproducing in surface waters (0–11.2 eggs fem day−1) but R. gigas and Calanoides acutus were largely resident in the warm deep water and undergoing their seasonal descent. A comparison with spring and summer data indicated increased abundance and biomass from spring through to summer followed by a decline towards autumn particularly over the shelf. Autumn values in oceanic waters differed little from summer. Mesozooplankton biomass in the surface 200 m of the oceanic stations as a proportion of that found in the top 1,000 m ranged from 63 to 78% of the total in spring and 62–73% in summer, but was only 23–29% of the total in this study, following redistribution down the water column.
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Acknowledgments
We thank Martin Collins, cruise leader of cruise JR100, for enabling this field work to take place within an already busy cruise schedule and Captain Jerry Burgan and his crew aboard RRS James Clark Ross for facilitating the scientific work under the sometimes difficult conditions. Beki Korb kindly provided the chlorophyll data and Mick Whitehouse constructed Fig. 3. This paper is a contribution from the FLEXICON project to the BAS DISCOVERY 2010 programme.
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Ward, P., Shreeve, R. & Tarling, G.A. The autumn mesozooplankton community at South Georgia: biomass, population structure and vertical distribution. Polar Biol 29, 950–962 (2006). https://doi.org/10.1007/s00300-006-0136-3
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DOI: https://doi.org/10.1007/s00300-006-0136-3