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Marine Ecology Progress Series

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MEPS 452:63-80 (2012)  -  DOI:

Austral fall−winter transition of mesozooplankton assemblages and krill aggregations in an embayment west of the Antarctic Peninsula

Boris Espinasse1, Meng Zhou2,*, Yiwu Zhu2, Elliott L. Hazen3, Ari S. Friedlaender3, Douglas P. Nowacek3, Dezhang Chu4, Francois Carlotti1

1Laboratoire d’Océanographie Physique et Biogéochimique, Centre Océanologique de Marseille, CNRS, Université de la Méditerranée, Campus de Luminy, Case 901, 13288, Marseille Cedex 09, France
2Department of Environmental, Earth and Ocean Sciences, University of Massachusetts Boston, 100 Morrissey Boulevard, Boston, Massachusetts 02125, USA
3Nicholas School of the Environment and Pratt School of Engineering, Duke University Marine Laboratory,
135 Duke Marine Lab Road, Beaufort, North Carolina 28516, USA
4National Oceanic and Atmospheric Administration Fisheries, 2725 Montlake Boulevard E, Seattle, Washington 98112, USA

ABSTRACT: To assess krill aggregations and humpback whale Megaptera novaeangliae foraging behavior, spatial and temporal relationships between Antarctic krill Euphausia superba and zooplankton taxonomic groups were studied during an interdisciplinary cruise conducted in May and June 2009 within Wilhelmina Bay on the western side of the Antarctic Peninsula. A vessel-mounted acoustic Doppler current profiler (ADCP) and a calibrated EK-60 echo sounder were used to assess circulation patterns and krill distributions in the bay, and a multiple opening and closing net (with 333 µm mesh) and environmental sensing system (MOCNESS) was used to collect live samples of mesozooplankton and krill for taxonomic composition analysis. The results from this field study complement a previous one that examined an anticyclonic bay-scale circulation of Antarctic krill. This super-aggregation of krill covered ~100 km2, had a concentration of 1000s of individuals m–2 and was associated with more than 306 humpback whales present in Wilhelmina Bay. Our results from the mesozooplankton study revealed that krill continuously conducted diel vertical migrations and formed aggregations in the inner bay, while the chlorophyll concentration at the surface decreased from 2.2 to 0.6 g C m−2 due to the decrease of daylight, and zooplankton concentrations increased from 0.5 to 1.5 g C m−2 probably from advective influx. Most zooplankton were distributed below 200 m while krill fed in the upper 150 m. The spatial and temporal correlations between krill and small- to medium-sized mesozooplankton imply that krill may become omnivorous when there is a lack of phytoplankton in the late austral fall. Though both phytoplankton and zooplankton biomasses contributed only small fractions of the daily ration needed for krill metabolism in Wilhelmina Bay, it is not clear what caused krill to aggregate on such a large scale, as this led to high mortality as a result of starvation and predation by whales and other top predators.

KEY WORDS: Antarctic Peninsula · Chlorophyll · Zooplankton · Krill · Food web · Austral fall

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Cite this article as: Espinasse B, Zhou M, Zhu Y, Hazen EL and others (2012) Austral fall−winter transition of mesozooplankton assemblages and krill aggregations in an embayment west of the Antarctic Peninsula. Mar Ecol Prog Ser 452:63-80.

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