Factors that affect the nearshore aggregations of Antarctic krill in a biological hotspot

TitleFactors that affect the nearshore aggregations of Antarctic krill in a biological hotspot
Publication TypeJournal Article
Year of Publication2017
AuthorsBernard KS, Cimino M, Fraser W, Kohut J, Oliver MJ, Patterson-Fraser D, Schofield OME, Statscewich H, Steinberg DK, Winsor P
JournalDeep Sea Research Part I: Oceanographic Research Papers
Volume126
Pagination139-147
Date Published2017/08
ISBN Number0967-0637
Keywordsaggregation; Antarctic krill; Biological hotspots; Euphausia superba; physical-biological interactions; tide; wind
Abstract

Antarctic krill, Euphausia superba, is a highly abundant and ecologically important zooplankton species in the Southern Ocean. Regions of elevated Antarctic krill biomass exist around Antarctica, often as a result of the concentrating effect of bathymetry and ocean currents. Such areas are considered biological hotspots and are key foraging grounds for numerous top predators in the region. A hotspot of Antarctic krill biomass exists off the southern extent of Anvers Island, Western Antarctic Peninsula, and supports a population of Adélie penguins that feed almost exclusively on it, as well as numerous other top predators. We investigated the spatio-temporal variability in Antarctic krill biomass and aggregation structure over four consecutive summer seasons, identifying environmental factors that were responsible. We identified three distinct krill aggregation types (Large-dense, Small-close and Small-sparse), and found that the relative proportion of each type to total aggregation numbers varied significantly between survey days. Large-dense aggregations occurred more frequently when westerly winds predominated and when the local mixed tide was in the diurnal regime. Small-close aggregations were also more frequent during diurnal tides and were negatively correlated with phytoplankton biomass. Small-sparse aggregations, on the other hand, were more prevalent when the mixed tide was in the semi-diurnal phase. We suggest that, under certain conditions (i.e. diurnal tides and westerly winds), the biological hotspot in the nearshore waters off Palmer Station, Anvers Island, functions as a zone of accumulation, concentrating krill biomass. Our findings provide important information on the dynamics of Antarctic krill at the local scale.

DOI10.1016/j.dsr.2017.05.008
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