6 research outputs found
Super-Aggregations of Krill and Humpback Whales in Wilhelmina Bay, Antarctic Peninsula
Ecological relationships of krill and whales have not been explored in the Western Antarctic Peninsula (WAP), and have only rarely been studied elsewhere in the Southern Ocean. In the austral autumn we observed an extremely high density (5.1 whales per km2) of humpback whales (Megaptera novaeangliae) feeding on a super-aggregation of Antarctic krill (Euphausia superba) in Wilhelmina Bay. The krill biomass was approximately 2 million tons, distributed over an area of 100 km2 at densities of up to 2000 individuals m−3; reports of such ‘super-aggregations’ of krill have been absent in the scientific literature for >20 years. Retentive circulation patterns in the Bay entrained phytoplankton and meso-zooplankton that were grazed by the krill. Tagged whales rested during daylight hours and fed intensively throughout the night as krill migrated toward the surface. We infer that the previously unstudied WAP embayments are important foraging areas for whales during autumn and, furthermore, that meso-scale variation in the distribution of whales and their prey are important features of this system. Recent decreases in the abundance of Antarctic krill around the WAP have been linked to reductions in sea ice, mediated by rapid climate change in this area. At the same time, baleen whale populations in the Southern Ocean, which feed primarily on krill, are recovering from past exploitation. Consideration of these features and the effects of climate change on krill dynamics are critical to managing both krill harvests and the recovery of baleen whales in the Southern Ocean
The overwintering of Antarctic krill, Euphausia superba, from an ecophysiological perspective
A major aim of this review is to determine
which physiological functions are adopted by adults and
larvae to survive the winter season with low food supply
and their relative importance. A second aim is to clarify the
extent to which seasonal variation in larval and adult krill
physiology is mediated by environmental factors with a
strong seasonality, such as food supply or day light. Experimental
studies on adult krill have demonstrated that speciWc
physiological adaptations during autumn and winter,
such as reduced metabolic rates and feeding activity, are
not caused simply by the scarcity of food, as was previously
assumed. These adaptations appear to be inXuenced
by the local light regime. The physiological functions that
larval krill adopt during winter (reduced metabolism,
delayed development, lipid utilisation, and variable growth
rates) are, in contrast to the adults, under direct control by
the available food supply. During winter, the adults often
seem to have little association with sea ice (at least until
early spring). The larvae, however, feed within sea ice but
mainly on the grazers of the ice algal community rather
than on the algae themselves. In this respect, a miss-match
in timing of the occurrence of the last phytoplankton
blooms in autumn and the start of the sea ice formation, as
has been increasingly observed in the west Antarctic Peninsula
(WAP) region, will impact larval krill development
during winter in terms of food supply and consequently the
krill stock in this region