Source, density and composition of sympagic fauna in the Barents Sea OLE J. LBNNE and BJBRN GULLIKSEN bnne, 0. J. & Gulliksen, B. 1991: Source, density and composition of sympagic fauna in the Barents Sea. Pp. 28%294 in Sakshaug, E., Hopkins, C. C. E. & Britsland, N. A. (eds.): Proceedings of the Pro Mare Symposium on Polar Marine Ecology, Trondheim, 12-16 May 1990. Polar Research lO(1). The sympagic fauna (= ice fauna) of the Barents Sea was investigated on nine different cruises in 1982- 1988. Each cruise lasted from two to five weeks. Sampling techniques were based on scuba diving. The most abundant sympagic organisms were the polar cod (Boreogadus saida) and the three amphipods Apherusa glacialis, Onisimus sp. and Gammarus wilkitzkii. Mean biomass-values (wet weight) of the invertebrate sympagic fauna ranged from 0 to 2 g/m2. Values above 0.001 g/m2 were not recorded in five of the nine cruises. This is orders of magnitude lower than mean values recorded in multi-year ice north of Svalbard and in the Fram Strait where values between 1- 10 g/m2 are quite common. Apherusa glacialis seemed to have the best spreading capacity of the three most conspicuous amphipods. Gammarus wilkitzkii was most dependent on a passive transport with the ice. Sympagic amphipods play an important part in a food chain from microalgae to polar cod and marine birds in areas covered with ice, especially in areas with multi-year ice. Ole J. Lmnne and Bjgrn Gulliksen, Departmenf of Marine Biology, Tromsm Museum, University of Trams@, N-9000 Troms), Norway. Present address: The Norwegian College of Fishery Science, Unioersity of Tromsg, N-9000 Tromsc. Norway. Introduction The word “sympagic” means “with ice”, and The Barents Sea, one of the marginal seas to the we use this term to include all animals that live Arctic Ocean, is seasonally partly covered with at least temporarily in or on the submerged parts ice. The average water-depth is about 230m of the sea ice. Species are assigned to the sympagic (Wassmann & Sakshaug 1987). Water depths less assemblage of animals on the basis of observations than 50m are found on Spitsbergenbanken and of their actual presence (temporary or perma- in nearshore areas only. The Barents Sea is, in nent) in the ice or on the ice surface. Our present the north, partly separated from the Arctic Ocean understanding of the structure and composition proper with a small number of islands situated of sympagic assemblages is to a large extent based between Nordaustlandet (Svalbard) and Frans on sampling and observations using scuba tech- Josef Land. niques. Most of our data, and data previously The age and origin of the sea ice in the Barents published by others, have been gathered from Sea is variable. Usually it is a mixture of locally areas near shore-based stations or from ships produced first-year (FY) ice and multi-year (MY) working along the rim of the Arctic basin. Water ice, in addition to the similar sea ice types depth and the duration of the ice-covered season imported from the Arctic Ocean. There may be affect composition and density of sympagic assem- considerable variation in the relationship between blages in such areas (Carey 1985). the different components (Vinje 1985). The ice There are fewer data available from areas with cover reaches its maximum extent in February to a permanent cover of sea ice. Year-round studies May and may extend south of Bj~rn~ya.Most of from the Soviet ice drift station NP23 in the the FY ice melts by the end of August. By that central Arctic Basin, however, have shown that time, in most years, the ice edge has retreated to a unique assemblage of species exists and utilises north of Kong Karls Land in the northern Barents the ice substrate throughout its life cycle. Sym- Sea (Vinje 1985). Areas north of Svalbard and pagic species therefore have been divided into an Frans Josef Land are dominated by MY ice from autochthonous group consisting of the permanent the perennial sea ice zone. residents of the ice and an allochthonous group 290 Ole J. L~nne& Bjorn Gulliksen consisting of temporary residents (Mel’nikov & yrocerus anguipes were relatively rare. Nereis pel- Kulikov 1980). agica (epitoke stage), calanoid copepods (Calanus The link between the sympagic assemblages finmarchicus. C. glacialis), the eaphausiid Thy- occupying FY ice and assemblages associated with sanoessa inermis. the amphipod Parathemisto lib- MY ice has attained little attention. The aim of elluh and others (Table 1) were also recorded, this paper is to focus on the variations in density but we regarded these organisms at present as and relative distribution of the sympagic fauna planktonic and not belonging to the sympagic found in the seasonally ice-covered Barents Sea fauna. and to compare our findings with similar data The most frequently occurring sympagic organ- from the perennial sea ice zone further north. ism in the Barents Sea is A. glacialis. This species, which had a mean wet weight of O.OO58 ? 0.0022 g in the 1988 data, is mainly attached to the lower surface of the ice and on some occasions to the Material and methods vertical floe edges. It is not usually associated The sympagic faunal communities in the Barents with brine channels or crevices in the ice. Sea were studied on nine different cruises in 1982- Onisirnus sp. occurred on the ice surface, but 1988, each lasting from two to five weeks (Gul- was more often found within small cracks and liksen 1984; L~nne& Gulliksen 1991a). The holes. Its mean weight in our 1988 samples were cruises in the Barents Sea have together spanned almost an order of magnitude higher than A. the months from February through October. The glacialis, 0.01350 k 0.0728 g. In 1988, floating sympagic iauna within the perennial sea ice zone algal clumps were frequently recorded in holes in north of Svalbard and in the Fram Strait were the ice, and Onisimus sp. were usually associated studied on two different cruises in 1986 and 1988 with these. Individuals sampled in these clumps (L~nne& Gulliksen 1991b). were often the same colour as the algae. Sampling in the field was based on different The largest of the amphipods was G. wilkitzkii, techniques using scuba equipment. This included which in the Barents Sea in 1988 had a mean the use of a suction sampler especially designed weight of 0.07280 k 0.0600 g. Juveniles and for collection of organisms on rough surfaces, in young adults were most common in these samples. brine channels and from other habitats that are G. wilkitzkii is almost always found inside small difficult to reach (L~nne1988). Also used were a holes or channels. If disturbed, it retracts and plankton net with a straight upper frame suitable instantly attaches itself to the walls of the channels to haul along flat undersurfaces of the ice (Gul- by the spiny appendages on pleopods six and liksen 1984), underwater-photography, and in situ seven. observations. To quantify the abundance of the The polar cod, B. saida, is mostly observed sympagic organisms, suction samples were taken between sandwiched ice floes or in melting holes within specific time intervals. Predetermined and crevices of the ice (L~nne& Gulliksen 1989). areas of the undersurface were scraped and photo- All specimens captured in the ice belonged to graphs of the organisms were taken within ref- year-class I or 11. Older fish descend to greater erence-frames of known sizes. (See L~nne& depths during spawning (Ponomarenko 1968). Gulliksen 1991a. b for detailed descriptions of The absence of other year-classes in the samples sampling techniques and sampling locations). support the view that spawned polar cod do not return to the surface. No reliable values for the density of polar cod could be calculated, partly due to their patchy density and their mobility. Results and discussion They are difficult to collect between sandwiched Three amphipods. Apherusa glacialis, Onisimus ice floes. and the couple of hundred individuals sp. and Gammarus wilkitzkii, and the polar cod, we were able to catch using hand-held dip nets Boreogadw saida. were the most abundant sym- required several hours of diving. pagic macro-organisms in the ice of the Barents Sea. Onisimus sp. is most probably 0. glacialis Variation in biomass and abundance only, but since it is difficult to distinguish from 0. nanseni it is denoted as Onisimus sp. The The total biomass of invertebrate sympagic fauna amphipods Gammaracanthus loricatus and Isch- in individual localities in the Barents Sea usually Sympagic fauna in the Barents Sea 291 Table 1. The relative occurrence of species collected in the Barents Sea (SSIZ) and north of Svalbard (PSIZ). SSIZ PSIZ Year: 1982 1983 1985 1986 1986 1987 1987 1988 1988 1986 1988 Month: Aug. M.4. A.-M. Apr. M.-J. F.-M. Oct. Mar. May J.-A. Sep. Annelida Polychaeta Nereis pelagica * Harmathoinae ind. X X X Mollusca Limacina sp. X X X Crustacea Ostraccda Ostracoda ind. X Copepoda Calanus spp. xxx xx xx X X Mysidacea Mysis sp. X X X Amphipoda * Apherusa glacialis xxx xxx X xx X X xx xxx xxx xxx Onisimus spp. xx xx X xx X X xx xxx xxx xxx * Gammarus wilkitzkii xxx x X X xx X X xx xx xxx xxx Gammaracanthus loricatus X X xx Parathemisto libellula X X X X X X X X * Weyprechtia pengub X Anonyx nugax X * Ischyrocerus anguipes X Amphipoda ind X X X X X Euphausiacea Thysanoessa inermis X X X X Decapoda Fandalus sp.