INTRODUCTIONIn the Northern Hemisphere, sea-ice extent varies from a minimum of 7.0 × 10 6 km 2 in September to a maximum of 15.4 × 10 6 km 2 in March (Parkinson et al. 1999). Sea ice is recognized as playing a significant role in the biology and ecology of polar marine systems, supporting a productive community of microalgae as well as a diversity of heterotrophs ranging from bacteria to metazoa (Carey & Montagna 1982, Carey 1985, Laurion et al. 1995, Gradinger & Zhang 1997. Most of the studies on the sea-ice biota in the Arctic Ocean and adjacent seas have been restricted to the coastal fast-ice, probably because of easier access compared to pack ice. With the recent development of highly sophisticated supports, investigations on ice floes have become feasible. Recently, studies of autotrophic and heterotrophic components of sea ice have been carried out on packice systems in the Barents, Laptev, and Greenland Seas and in the central Arctic Ocean (Gradinger et al. 1992, 1999, Friedrich 1997, Melnikov 1997, Gradinger 1999 ABSTRACT: The abundance, biomass, composition and grazing impact of the bottom sea-ice meiofauna were investigated in the North Water, High Arctic, during April and May 1998. Sampling was conducted on both pack ice and land fast-ice. At the lowermost 2 to 4 cm of the sea ice, chlorophyll a reached a maximum concentration of 55.7 mg m -2. Sea-ice meiofauna were observed only at the ice bottom, and were composed of nematodes, copepods (harpacticoids and cyclopoids), crustacean nauplii, polychaete larvae and turbellarians. Total abundance of sea-ice meiofauna ranged from 0 to 34 500 ind. m -2 at the sampling stations. Nematodes were the most abundant taxon in the ice, with highest densities at a land fast-ice station. Highest abundances of copepods as well as crustacean nauplii were observed in the pack ice. The total sea-ice meiofauna biomass varied between 0 and 19.4 mg C m -2 . Potential ingestion rates, determined using allometric equations, indicated that seaice meiofauna never consumed more than 0.9% of the ice-algae standing stock and 5.7% of the daily ice-algae production. These calculations strongly suggest that the grazing impact of sea-ice meiofauna on ice algae was negligible in the North Water in early spring. The low standing stock of ice meiofauna also precludes their potential as an important food source for higher trophic levels. Meiofauna, therefore, appear to be a minor contributor to the overall carbon flow in the sea-ice biota of the North Water during spring. KEY WORDS: Arctic polynya · Sea ice · Algae · Meiofauna · Grazing impactResale or republication not permitted without written consent of the publisher

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Nematode species from three intertidal assemblages (St Lawrence Estuary, Quebec, Canada) were studied in order to form an ecological interpretation of three allometric attributes: body width, size spectra, and morphotypes. The three assemblages were characterized by a very similar sediment grain median (Md) but different silt–clay proportions: A1 (upper-tidal level; Md=122 μm; silt=34.8%), A3 (mid-tidal level; Md=182 μm; silt=12.8%), and A5 (lower-tidal level; Md=122 μm; silt=6.8%). Silt–clay proportions were an influential factor in determining the mean nematode body width, used as a morphological discriminant between burrowing and interstitial organisms. A plot of the number of species vs the body width-classes showed two peaks: between 19.3 and 22.6 μm (interstitial), and between 32.0 and 45.5 μm (burrowers). As for the size spectra, in sandy sediments the mean nematode individual biomass was smaller than in muddy sediments. As a consequence, the estimated mean individual respiration rate was greater in muddy (A1=2.26 nl O2 h−1) than sandy sediments (A3=1.25 nl O2 h−1; A5=1.12 nl O2 h−1). In contrast, estimated metabolic ratios were lower in A1 (2.78 nl O2 h−1 μg−1 dry weight, DW) than in A3 (2.95 nl O2 h−1 μg−1 DW) and A5 (3.01 nl O2 h−1 μg−1 DW) suggesting different productivity and/or physiological adaptations to different lifestyles (burrowing vs interstitial) between species inhabiting muddy or sandy sediments. Morphotypes (body width/body length ratio=w/l ratio) were found to be associated with feeding groups. Small w/l ratios were typical of microvores, while greater ratios were typical of epigrowth feeders and predators. Ciliate-feeders, deposit-feeders and facultative predators had intermediate ratios. A morphotype food-related hypothesis is proposed: the species morphotype reflects the quality of exploited food; a small w/l ratio (i.e. long gut) would favour digestive efficiency and would be an adaptation to low quality food (microvores); inversely, a greater w/l ratio (i.e. short gut) would be an adaptation to high quality food (epigrowth-feeders and predators).

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