No abstract

The fate of first-year ice algae production was assessed from April to June 1998, in the North Water Polynya. A landfast ice station was regularly visited and sampled for biomass, composition, and production of bottom ice algae, composition and grazing of the bottom ice meiofauna, and under-ice sedimentation. The latter was assessed using particle interceptor traps, which were installed at 1 m underneath the ice. The composition, carbon biomass and grazing of the bottom ice microfauna were also assessed at various stations within the polynya. A carbon budget for ice production and export, including meio-and microfauna grazing and sedimentation, was calculated based on 2 independent estimates. At the landfast ice station, the ice algae community was strongly dominated by pennate diatoms, with Nitzschia frigida averaging 85% of total cell numbers. The biomass of microheterotrophs and microautotrophs was less than 1% of total bottom ice carbon at the stations visited. Heterotrophic dinoflagellates and ciliates dominated the bottom ice microfauna community. Size-frequency distributions for the dominant ciliates (Strombidium spp. and hypotrichs) and dinoflagellates suggest that only the latter were able to utilise ice diatoms as a food resource. There was good agreement between carbon budget estimates and results showed that very little ice algal production was channelled through the meio-and microfauna within the ice. The bulk of the bottom ice carbon biomass was readily exported to the water column through direct sinking (75% of ice export). These results stress that the main flow of organic carbon at the ice-water interface was through sedimentation of ice algae and suggest that food-web interactions within the ice do not influence the availability of ice algae to pelagic grazers, in seasonally ice covered areas.KEY WORDS: Protists · Dinoflagellates · Ciliates · Sedimentation · Carbon cycling · Sea ice · Ice algae Resale or republication not permitted without written consent of the publisherAquat Microb Ecol 30: [57][58][59][60][61][62][63][64][65][66][67][68] 2002 Michel et , Mock & Gradinger 2000. However, the role of grazers in the cycling of carbon in ice communities has, so far, received less attention (Vézina et al. 1997).In the Arctic, the importance of ice algal production for under-ice amphipods and metazooplankton grazers has been reported, based on both direct (Conover et al. 1986a, Runge & Ingram 1988, Werner 1997 and indirect (Michel et al. 1996, Scott et al. 1999) assessments. Results from an annual study in West Greenland also suggest that ice algae could serve as food for pelagic protozoans (Levinsen et al. 2000). With regard to grazing within the ice, previous work on meiofauna in annual Arctic sea ice generally suggest that a minor fraction of ice algae production is cycled through this pathway (Gradinger 1999. However, grazing by meiofauna can control biomass accumulation in Greenland pack ice in summer . Studies on ice microheterotrophs have focussed primarily on the composition of...

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

No abstract