No abstract

The Young Sound estuary was covered by sea ice for approximately 10 mo during 1996. Investigations of pelaglc primary production and est~mated grazing were performed during the summer thaw (20 June to 25 August) and in the winter month of February. The phytoplankton community was dominated by diatoms in the surface samples, as well as in the subsurface bloom succeeding the spring bloom. Pelagic primary production was l~mited by light during sea ice cover After break-up of the sea ice, silicate initially limited primary production in the surface water due to a well-established pycnocline, and maximum photosynthesis occurred in a subsurface layer at 15 to 20 m depth. In August, production sank to deeper water layers presumably due to nitrogen limitation. The carbon budget describing the fate of the annual pelagic primary production in Young Sound reveals that the pelagic production of -10 g C m-2 yr-' was tightly coupled to the grazer community, since total consumption by the grazer community amounted to 10-12 g C m-2 yr-'. The classical food web dominated this northeastern Greenlandic fjord, and it was estimated that copepods account for >80% of the grazing pressure upon phytoplankton. Based on this study and other values of annual pelagic primary production and sea ice cover found in the literature, we suggest that annual pelagic primary production in the Arctic can be described as proportional to the length of the open water light period. We propose that annual pelaglc pnmary production, and hence secondary production, in a wide range of Arctic marine areas may increase in the future as a consequence of reduction and thinning of sea ice cover due to global warming.

Stabilin-2, the hepatic hyaluronan receptor, has recently been cloned by us. Together with stabilin-1, stabilin-2 constitutes a novel family of fasciclin-like hyaluronan receptor homologues. Here, we analyzed expression of stabilin-2 (mStab-2) in a broad array of C57BL/6 mouse organs and tissues. While northern blot analysis showed positive expression of mStab-2 mRNA confined to liver and spleen, immunohistochemistry demonstrated mStab-2 protein expression in the endothelial sinuses of liver, lymph nodes, spleen, and bone marrow, and in specialized structures of eye, heart, brain, and kidney. Expression of mStab-2 was detected in corneal and lens epithelium, in mesenchymal cells of the heart valves, in the ependymal cells lining the ventricles in the brain, and in the prismatic epithelial cells covering the renal papillae. In pathological conditions, such as tumor growth or wound healing processes, mStab-2 was not expressed in the newly formed vasculature or other tissue components. Based on these results, we suggest that mStab-2 might be involved in the clearance of hyaluronan from the lymph or the blood circulation via the network of endothelial sinuses. At the other mStab-2-positive tissues sites that are either avascular and/or demarcate a solid/liquid interface, mStab-2 may serve to maintain tissue integrity by supporting extracellular matrix turnover or it may contribute to maintaining fluidity of bodily liquids by resorption of hyaluronan.

Pelagic food web structure and carbon dynamics were studied in Disko Bay, western Greenland, following the breakup of the sea ~c e in June-July 1992. Disko Bay was influenced by meltwater, and calm sunny weather heated the surface water from 0 to 6°C. lnitially a dlatom bloom was present throughout the p h o t~c zone. Due to nutrlent depletion, and deepening of the surface layer, the bloom left the photic zone. Active bacter~oplankton was observed from the first s a m p l~n g Bactenal production i.ncreased from a few percent to one-third of the primary production after the sedimentation of the bloom. The grazing impact by the copepod community was assessed by 2 independent methods. The gut fluorescence method and the egg production method resulted in copepod grazing estimates of about 80 and 4 5 % of the primary production d -l , respectively. Carbon budget considerations showed that the estimated protozooplankton grazing impact was comparable, or higher, than grazing by the Calanus spp. dominated copepod community. The observed importance of Arctic bacteria and protozooplankton stress that high latitude pelagic food webs potentially have the same trophic complexity as low latitude pelagic ecosystems.