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Fin whales (Balaenoptera physalus quoyi) of the Southern Hemisphere were brought to near extinction by twentieth century industrial whaling. For decades, they had all but disappeared from previously highly frequented feeding grounds in Antarctic waters. Our dedicated surveys now confirm their return to ancestral feeding grounds, gathering at the Antarctic Peninsula in large aggregations to feed. We report on the results of an abundance survey and present the first scientific documentation of large fin whale feeding aggregations at Elephant Island, Antarctica, including the first ever video documentation. We interpret high densities, re-establishment of historical behaviours and the return to ancestral feeding grounds as signs for a recovering population. Recovery of a large whale population has the potential to augment primary productivity at their feeding grounds through the effects of nutrient recycling, known as 'the whale pump'. The recovery of fin whales in that area could thus restore ecosystem functions crucial for atmospheric carbon regulation in the world's most important ocean region for the uptake of anthropogenic CO2. [ABSTRACT FROM AUTHOR]

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 specific 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 influenced 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. [ABSTRACT FROM AUTHOR]

The article presents an analysis of the seasonal variation of the adult krill's (Euphausia superba) metabolic activity, body composition, growth, and feeding in Lazarev Sea, Antarctica. It explores the three expeditions launched by the researchers in summer, mid autumn, and winter to gather krill sampling and study its body composition and growth. The researchers employ rectangular midwater trawl to collect krill samples and determine krill's measurement, color, size, and variety. The study observes that krill grow by 0.5 to 3.8 percent in length, decline in respiration rates is notable in autumn and winter, and krill's body lipids and proteins are consumed in winter. It adds that adult krill adopt metabolic delay and omnivorous feeding during winter.

The physiological condition of larval Antarctic krill was investigated during austral autumn 2004 and winter 2006 in the Lazarev Sea. The condition of larvae was quantified in both seasons by determining their body length (BL), dry weight (DW), elemental and biochemical composition, stomach content analysis, and rates of metabolism and growth. Overall the larvae in autumn were in better condition under the ice than in open water, and for those under the ice, condition decreased from autumn to winter. Thus, growth rates of furcilia larvae in open water in autumn were similar to winter values under the ice (mean, 0.008 mm d-1), whereas autumn underice values were higher (0.015 mm d-1). Equivalent larval stages in winter had up to 30% shorter BL and 70% lower DW than in autumn. Mean respiration rates of winter larvae were 43% lower than of autumn larvae. However, their ammonium excretion rates doubled in winter from 0.03 to 0.06 µg NH4 DW-1 h-1, resulting in mean O:N ratios of 46 in autumn and 15 in winter. Thus, differing metabolic substrates were used between autumn and winter, which supports a degree of flexibility for overwintering of larval krill. The larvae were eating small copepods (Oithona spp.) and protozoans, as well as autotrophic food under the ice. The interplay between under-ice topography, apparent current speed under sea ice, and the swimming ability of larval krill is probably critical to whether larval krill can maintain position and exploit suitable feeding areas under the ice. [ABSTRACT FROM AUTHOR]

Abstract: We investigated the effect of short-term starvation (18days) on the physiology of adult Euphausia superba from the Lazarev Sea at the onset of summer. Metabolic data, elemental and biochemical composition as well as morphological parameters revealed that, at the beginning of the experiment, krill was in transition from winter to summer physiology, with some features typical for late winter/spring (low lipid reserves, low C:N ratio, elevated O:N ratio) and others for summer (high respiration rates, high MDH activity, large green digestive gland, short intermoult period (IMP) and fast growth). Starvation reduced body reserves drastically by more than 1% C per day. In relative terms, lipids (40%) and glycogen (30%) were reduced most and proteins by 10% of the initial value. Absolute consumption, however, was approximately 4% DM for lipids and proteins each, whereas contribution of glycogen was negligible. Within lipids, triacylglycerols (TAG) and phospholipids (PL) fell most dramatically from already low levels by 84% and 39%, respectively. Phosphatylcholine (PC) constituted 57% of PL and declined by 46%. As a result, proportions of the lipid classes changed with sterols increasing relatively. Metabolite changes were similar in cephalothorax and abdomen, although TAG in the cephalothorax fell more drastically. High metabolic activity at the beginning of starvation was quickly reduced to reach 53% after 18days, accompanied by a reduction in the abdominal activity of malate dehydrogenase (MDH) by 25%. Our results may provide some explanation why recruitment of some year-classes of krill fails. Despite execution of the experiment in spring (i.e. transitional physiology state) and its short duration, some changes in the activity of metabolic enzymes in the abdomen, representing lipolytic, glycolytic and proteolytic pathways, respectively, were measured. Rising activities of 3-hydroxyacyl-CoA dehydrogenase (HOAD) and glyceralaldehyde-3-phosphate dehydrogenase (GAPDH) indicated increased lipolytic and glycolytic fluxes, respectively, whereas declining glutamate dehydrogenase (GluDH) activity suggests reduced proteolytic flux. Activities of other enzymes from protein catabolism, alanine aminotransferase (AlaAT) and aspartate aminotransferase (AspAT), however, remained unchanged. Ratios calculated from these trends indicated a declining importance of protein use during the course of starvation compared with consumption of lipids and glycogen. These results suggest that constant-proportion enzymes from different catabolic pathways, and calculated ratios thereof, may be useful in detecting shifts between the consumption of different body reserves. [Copyright &y& Elsevier]