b13C, 6I5N, and C/N were measured for each of 247 muscle tlssue samples from 12 blrd, 4 seal, and 4 fish species collected In the Weddell Sea primanly d u n n g March 1986 ht3C values ranged flom -31 3 to -22 O%o and, in the case of f~s h and seal san~ples, varied inversely with C/N T h~s ~m p l~e d that l~p i d concentratlon s~gn~ficantly influenced these vertebrate hI3C measurements No such relat~on-shlp was found between C/N and bI5N where the latter values ranged from + 4 4 to + l 1 2 % w~t h cons~derable overlap among many of the taxonomic groups measured Notable exceptions to thls were found in the Wilson s storm-petrel and the Kerguelan petrel, among whlch elevated bl'N values of some lndivlduals probably reflected feeding outslde of the Weddell Sea Significant feedlng on vertebrate biomass was ~n d~c a t e d by the 15N enrichment of the southern giant fulmar and several snow petrel ind~viduals Some d~e t separation among crabeater, Antarct~c fur, leopard, and Ross seals was also evldent Nevertheless, the overlap In hI5N among most Weddell Sea vertebrates, coupled with an observed range of vertebrate values that was considerably narrower than that of t h e~r potent~al pley supports the hypothesis that many of these h~g h e r consumers share a small number of common food resources and trophlc levels

Polar regions have experienced significant warming in recent decades. Warming has been most pronounced across the Arctic Ocean Basin and along the Antarctic Peninsula, with significant decreases in the extent and seasonal duration of sea ice. Rapid retreat of glaciers and disintegration of ice sheets have also been documented. The rate of warming is increasing and is predicted to continue well into the current century, with continued impacts on ice dynamics. Climate-mediated changes in ice dynamics are a concern as ice serves as primary habitat for marine organisms central to the food webs of these regions. Changes in the timing and extent of sea ice impose temporal asynchronies and spatial separations between energy requirements and food availability for many higher trophic levels. These mismatches lead to decreased reproductive success, lower abundances, and changes in distribution. In addition to these direct impacts of ice loss, climate-induced changes also facilitate indirect effects through changes in hydrography, which include introduction of species from lower latitudes and altered assemblages of primary producers. Here, we review recent changes and trends in ice dynamics and the responses of marine ecosystems. Specifically, we provide examples of ice-dependent organisms and associated species from the Arctic and Antarctic to illustrate the impacts of the temporal and spatial changes in ice dynamics.

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Proximate (protein, lipid, carbohydrate and chitin) and elemental (carbon and nitrogen) composition were determined for 18 species of Antarctic micronektonic Crustacea, representing the majority of species found in the Antarctic water column. Individuals used in the analyses were captured during fall and winter; for 8 species data were collected in both seasons. Seven of the 8 species showed some evidence that combustion of body stores were an aid to surviving the winter months; comparison with data from other investigators suggests that most of the species inhabiting shallow and mid-depths exhibit some degree of combustion of body stores during winter. Three types of overwintering stratey e s are proposed for Antarctic zooplankton and micronekton. Type 1, exhibited by some calanoid copepods, is characterized by accumulation of large lipid deposits and a true dormancy, or diapause, during winter. Type 2, exhibited by euphausiids and hyperiid amphipods, is characterized by a marked reduction in metabolic rate, combustion of body substance, opportunistic feeding, but no true dormancy. Type 3, 'business as usual' is exhibited by decapods and gammarid amphipods; it is characterized by an absence of a winter reduction in metabolic rate, combustion of body stores in some species but a lack of combustion or accumulation of energy in others, and opportunistic feeding. Overwintering scenarios computed for Euphausia superba suggest that the impact of the winter season is most severe in the smaller size classes.KEY WORDS: Proximate composition . Antarctic . Pelagic Crustacea . Overwinter INTRODUCTIONThe micronektonic crustacean assemblage of the Antarctic pelagial is a unique blend of cosmopolitan deep-living species and high-latitude endemics (Nagata 1986, Iwasaki & Nemoto 1987, Lancraft et al. 1989. In the Atlantic sector, most of the cosmopolitan species disappear from the water column at the Weddell-Scotia confluence, a physical boundary that defines the northern limit of winter sea ice and separates the low and high Antarctic ecosystems (Lancraft et al. 1989). Species living south of the confluence must contend with the seasonal advance and retreat of pack ice and its influence on water column irradiance; all species must deal with highly pulsed seasonal production and uniformly cold temperatures in the upper 1000 m of the water column. In the Weddell Sea region primary production varies from 560 mg C m-2 d-l during spring in the vicinity of the ice edge at 60°S, 40" W (Smith & Sakshaug 1990) to 25 mg C m-2 d-' during winter (June-August) in the same region (W. 0 .Extreme seasonality in primary production has its most severe impact on herbivorous Crustacea and, as a consequence, shapes their Me histories. Many species of the best-studied pelagic Crustacea, the calanoid copepods, accumulate large quantities of lipid during the productive season and enter a state of true dormancy, or diapause, during the non-productive season, resuming normal feeding activity at the onset of phytoplankton growth (Sargent & Hen...