Mesozooplankton assemblages in the shallow Arctic Laptev Sea in summer 1993 and autumn 1995

Mesozooplankton distribution and composition in the very shallow part of the Siberian Laptev Sea shelf were studied during the German-Russian expeditions “Transdrift I” (August/September 1993) and “Transdrift III” (October 1995). Maximum abundances were found close to the outflow of the Lena River (7,965 ind. m⁻³) and in the Yana river mouth (38,163 ind. m⁻³). Lowest abundances occurred in the northeast and west of the Laptev Sea (64–95 ind. m⁻³). Highest biomass values (104–146 mg DM m⁻³) were determined in the northern and northeastern part of the shallow Laptev Sea, as well as close to the river outflows, with a record biomass maximum in the Yana river mouth (270 mg DM m⁻³). Biomass minima were situated north of the Lena Delta and in the western part of the shallow Laptev Sea (0.3–1.0 mg DM m⁻³). Copepods dominated in terms of abundance and biomass. Cluster analyses separated four mesozooplankton assemblages: the assemblage “Lena/Yana” in the southern part, “Eastern-central” in the centre, “Kotelnyy” in the eastern part and “Taimyr” in the western part of the shallow Laptev Sea. The small-sized neritic and brackish-water copepods Drepanopus bungei, Limnocalanus grimaldii and Pseudocalanus major occurred in enormous numbers and made up the bulk of zooplankton abundance and biomass in the very shallow part of the Laptev Sea close to the rivers Lena and Yana. In the more northern and northeastern areas, Calanus glacialis, P. minutus and P. major were dominant copepod species, whereas Oithona similis and Acartia sp. became important in the western Laptev Sea. Appendicularians, as well as hydromedusae and the chaetognath Sagitta sp., contributed significantly to abundance and biomass, respectively, but not over the entire area studied. One can identify taxon-specific distribution patterns (e.g. Sagitta predominated the biomass in a zone between the area heavily influenced by Lena/Yana and the offshore area to the north), which differ from the patterns revealed by cluster analysis. Hydrographic features, especially the enormous freshwater inflow, apparently determine the occurrence and formation of zooplankton aggregations. Extremely high numbers of small-sized neritic and brackish-water copepods occurred locally, which were probably also supported by excellent feeding conditions.     

Breaking the ice: large-scale distribution of mesozooplankton after a decade of Arctic and transpolar cruises

Mesozooplankton collected during five summer expeditions to the Arctic Ocean between 1987 and 1991 was analysed for regional patterns in biomass and species distribution, distinguishing between an epipelagic (0–100 m) and a deeper (0–500 m) layer. A total of 58 stations was sampled mainly in the Nansen, Amundsen and Makarov Basins of the central Arctic Ocean and in areas of the Greenland Sea, West Spitsbergen Current and Barents Sea. Results from the different expeditions were combined to create a transect extending from the Fram Strait across the Eurasian Basin into the Makarov Basin. Mesozooplankton dry mass in the upper 500 m decreased from 8.4 g m⁻² in the West Spitsbergen Current to less than 2 g m⁻² in the high-Arctic deep-sea basins. In the central Arctic Ocean, biomass was concentrated in the upper 100 m and was dominated by the large copepods Calanus hyperboreus and C. glacialis. In contrast, the mesozooplankton in the West Spitsbergen Current was more evenly distributed throughout the upper 500 m, with C. finmarchicus as the prevailing species. The distribution of abundant mesopelagic species reflected the hydrographic regime: the calanoid copepod Gaetanus tenuispinus and the hyperiid amphipod Themisto abyssorum were most abundant in the Atlantic inflow, while Scaphocalanus magnus was a typical component of the high-Arctic fauna. The relatively high mesozooplankton biomass and the occurrence of boreal-Atlantic species in the central Arctic Ocean are indicators for the import of organic material from allochthonous sources, especially from the northern North Atlantic. Hence, in spite of its enclosure by land masses, the Arctic Ocean is characterized by an exchange of water masses and organisms with the North Atlantic, and advection processes strongly influence the distribution of plankton species in this high-latitude ecosystem. Received: 18 December 1997 / Accepted: 11 April 1998     

Vertical distribution of bacteria in Arctic sea ice from the Barents and Laptev Seas

The vertical distribution of bacterial abundance and biomass was investigated in relation to algal biomass in ice cores taken from drifting ice floes in two Arctic shelf areas: the Barents Sea and the Laptev Sea. Bacteria were not homogeneously distributed throughout the cores but occurred in dense layers. Different types of distribution patterns were found: either a single maximum occurred inside or at the bottom of the ice floe or maxima were found in different parts of the floes. Bacterial concentrations ranged from 0.4 to 36.7 · 10⁵ cells ml⁻¹. The size spectra of sea-ice bacteria were determined by image analysis. Cell sizes showed considerable variation between the ice floes. In multi-year sea ice, the largest bacteria were observed in the area of an internal chlorophyll a maximum. No specific vertical distribution patterns were found in first-year ice floes. Bacterial biomass for the ice cores ranged from 19.2 to 79.2 mg C m⁻², and the ratio of bacterial:ice algal biomass ranged from 0.43 to 10.42. A comparison with data collected from fast ice revealed large differences in terms of cell size, abundance and biomass. Received: 7 September 1995 / Accepted: 10 September 1996     

Reproduction of Calanus glacialis in the Laptev Sea, Arctic Ocean

Abundance and reproductive biology (gonad maturation and egg production) of the Arctic copepod Calanus glacialis were studied in the Laptev Sea and adjacent Arctic Ocean in September 1993 and from July to September 1995. Both abundance and reproductive activity were subject to strong spatial and seasonal variability, which was related to the ice cover, feeding conditions and circulation pattern. Maximum abundance of the C. glacialis population was generally confined to the outer shelf and slope with depths between 50 and 1000 m. During both cruises, highest egg production rates and largest number of young copepodite stages were observed in the eastern Laptev Sea, where the development of the C. glacialis population seems to follow the opening of the “Siberian Polynya”. In the western part, which is usually covered by pack ice, females were all immature, and no young stages were found. However, females responded quickly to a temporary opening of the ice there in 1995 and spawned. Starvation experiments showed that food-independent reproduction fuelled by internal energy resources was at least partly responsible for relatively high egg production rates at low ambient food concentrations. Egg production rates in starved females were considerably higher than those previously reported. Accepted: 14 June 2000     

Distribution patterns of diatom surface sediment assemblages in the Laptev Sea (Arctic Ocean)

The modern diatom distribution in the Laptev Sea, Arctic Ocean, was investigated in 89 surface sediment samples. Diatom concentrations are relatively low showing values between 0.01×10⁶ and 6.7×10⁶ valves per gram dry sediment. Based on a factor analysis using seventeen taxa or taxa groups five diatom surface sediment assemblages can be defined: the ice diatom assemblage of the central region of the Laptev Sea, the Chaetoceros assemblage of the eastern and southeastern shelf, the Thalassiosira antarctica assemblage of the continental slope and deep sea, the freshwater diatom assemblage in the vicinity of river mouths and deltas, and the Thalassiosira nordenskioeldii assemblage which shows a patchy occurrence on the central Laptev Sea shelf. The distribution pattern of diatom assemblages in surface sediment is significantly related to oceanographic conditions of surface water masses. The main factors controlling the distribution of diatoms in the Laptev Sea are the riverine freshwater input during the summer which strongly affects the salinity conditions, and the sea-ice extent. Furthermore, the composition of the Thalassiosira antarctica assemblage of the continental slope is largely influenced by dissolution and lateral transport processes.     

Integrated abundance and biomass of sympagic meiofauna in Arctic and Antarctic pack ice

The abundance and biomass of sympagic meiofauna were studied during three cruises to the Antarctic and one summer expedition to the central Arctic Ocean. Ice samples were collected by ice coring and algal pigment concentrations and meiofauna abundances were determined for entire cores. Median meiofauna abundances for the expeditions ranged from 4.4 to 139.5 × 10³ organisms m⁻² in Antarctic sea ice and accounted for 40.6 × 10³ organisms m⁻² in Arctic multi-year sea ice. While most taxa (ciliates, foraminifers, turbellarians, crustaceans) were common in both Arctic and Antarctic sea ice, nematodes and rotifers occurred only in the Arctic. Based on the calculated biomass, the potential meiofauna ingestion rates were determined by applying an allometric model. For both hemispheres, daily and yearly potential ingestion rates were below the production values of the ice algal communities, pointing towards non-limited feeding conditions for ice meiofauna year-round. Accepted: 29 March 1999     

Composition and distribution of mesozooplankton in the Nansen Basin,Arctic Ocean,during summer

Information about the large-scale zooplankton distribution in the Nansen Basin, that part of the Arctic Ocean most directly influenced by the inflow of Atlantic Water, is still scarce. During the Polarstern expedition ARK IV/3 in July/August 1987 zooplankton from the upper 500 m was sampled along two transects across the western Nansen Basin. Spatial variations in faunal composition, abundance, and biomass are described. Special emphasis is given to the distribution patterns and possible drifting routes of species advected into the Arctic Ocean through Fram Strait. Forty-five species and eight taxa not determined to species level were identified. Copepods clearly dominate in terms of species number, abundance, and biomass. Ostracods and chaetognaths comprise the most important groups of the non-copepod zooplankton. Maximum species numbers were recorded over the abyssal plain around 83°N. Total abundance and biomass decreased by more than 80% towards the northern part of the basin. Cluster analysis revealed two major faunal assemblages, broadly overlapping over the central Nansen Basin, and three principal types of spatial distribution. The well-defined zonation observed in the large-scale zooplankton distribution closely resembles the major hydrographic and topographic features. The opposite movement of the Polar Surface Water and the Atlantic Water in the southern Nansen Basin might cause pronounced deviations between the drifting routes of species with different water mass preferences advected through Fram Strait.     

Biogeography and Photosynthetic Biomass of Arctic Marine Pico-Eukaroytes during Summer of the Record Sea Ice Minimum 2012

Information on recent photosynthetic biomass distribution and biogeography of Arctic marine pico-eukaryotes (0.2–3 μm) is needed to better understand consequences of environmental change for Arctic marine ecosystems. We analysed pico-eukaryote biomass and community composition in Fram Strait and large parts of the Central Arctic Ocean (Nansen Basin, Amundsen Basin) using chlorophyll a (Chl a) measurements, automated ribosomal intergenic spacer analysis (ARISA) and 454-pyrosequencing. Samples were collected during summer 2012, the year with the most recent record sea ice minimum. Chl a concentrations were highest in eastern Fram Strait and pico-plankton accounted for 60–90% of Chl a biomass during the observation period. ARISA-patterns and 454-pyrosequencing revealed that pico-eukaryote distribution is closely related to water mass distribution in the euphotic zone of the Arctic Ocean. Phaeocystaceae, Micromonas sp., Dinophyceae and Syndiniales constitute a high proportion of sequence reads, while sequence abundance of autotrophic Phaeocystaceae and mixotrophic Micromonas sp. was inversely correlated. Highest sequence abundances of Phaeocystaceae were observed in the warm Atlantic Waters in Fram Strait, while Micromonas sp. dominated the abundant biosphere in the arctic halocline. Our results are of particular interest considering existing hypotheses that environmental conditions in Nansen Basin might become more similar to the current conditions in Fram Strait. We propose that in response, biodiversity and biomass of pico-eukaryotes in Nansen Basin could resemble those currently observed in Fram Strait in the future. This would significantly alter biogeochemical cycles in a large part of the Central Arctic Ocean.     

The metazoan meiobenthos along a depth gradient in the Arctic Laptev Sea with special attention to nematode communities

The meiobenthos along a depth transect of oligotrophic sediments in the Arctic Laptev Sea was studied. The meiobenthos followed the general trends reported from other studies: densities decreased with depth in relation to the more limited supply of degradable organic matter at greater depths. Although the sediments along the transect were poor in organic matter in comparison with the NE Atlantic, the densities fitted well with the meiobenthic densities reported from the latter area. It is suggested that the meiobenthos in the cold polar waters is adapted to this extreme environment by a rapid response to short food pulses to the sediments. Nematodes were identified up to genus level and assigned to trophic groups. A total of 32 families comprising 95 genera were found along the transect. The communities were dominated by deposit feeders whose importance increased with depth. Both TWINSPAN and CCA analyses revealed a community shift along the depth transect: a shelf community dominated by Microlaimus and Chromadora could be distinguished from a slope community dominated by Monhystera and Leptolaimus. Generic diversity decreased with depth. Received: 15 March 1997 / Accepted: 29 June 1997     

Landlocked Arctic charr (Salvelinus alpinus) population structure and lake morphometry in Greenland – is there a connection?

Landlocked Arctic charr (Salvelinus alpinus) populations in sub-Arctic and Arctic Greenland lakes were sampled with multi-mesh-sized survey gillnets. The study covered a range of small shallow lakes (0.01 km², maximum depth <3.3 m) to large deep lakes (43 km², maximum depth >200 m). Arctic charr were found in one to three different forms in lakes with maximum depths >3 m. A dwarf form occurred in all lakes inhabited by Arctic charr and was the only form in lakes with maximum depths <8 m. In deeper lakes with maximum depths >20 m and a surface area <0.5 km², larger charr were found, although in low numbers, the length-frequency distribution being unimodal with a tail towards large sizes. In lakes with a maximum depth >20 m, large-sized charr were more abundant, and the length-frequency distribution of the population was bimodal, with a first mode around 10–12 cm and a second mode around 26–37 cm. In a single large and deep lake, a distinct medium-sized pelagic zooplankton-eating charr form occurred. Maximum size of individual charr was significantly positively correlated with lake maximum depth and volume, and the mean size of large-sized charr was significantly positively correlated with lake volume. Our study indicates that the charr population structure became more complex with increasing lake size. Moreover, the population structure seemed to be influenced by lake-water transparency and the presence or absence of three-spined stickleback (Gasterosteus aculeatus). Accepted: 31 January 2000     

Phytoplankton biomass and primary production in the marginal ice zone of the northwestern Weddell Sea during austral summer

During the austral summer of 1995, distributions of phytoplankton biomass (as chlorophyll a), primary production, and nutrient concentrations along two north-south transects in the marginal ice zone of the northwestern Weddell Sea were examined as part of the 8th Korean Antarctic Research Program. An extensive phytoplankton bloom, ranging from 1.6 to 11.2 mg m⁻³ in surface chlorophyll a concentration, was encountered along the eastern transect and extended ca. 180 km north of the ice edge. The spatial extent of the bloom was closely related to the density field induced by the input of meltwater from the retreating sea ice. However, the extent (ca. 200 km) of the phytoplankton bloom along the western transect exceeded the meltwater-influenced zone (ca. 18 km). The extensive bloom along the western transect was more closely related to local hydrography than to the proximity of the ice edge and the resulting meltwater-induced stability of the upper water column. In addition, the marginal ice zone on the western transect was characterized by a deep, high phytoplankton biomass (up to 8 mg Chl a m⁻³) extending to 100-m depth, and the decreased nutrient concentration, which was probably caused by passive sinking from the upper euphotic zone and in situ growth. Despite the low bloom intensity relative to the marginal ice zone in both of the transects, mean primary productivity (2.6 g C m⁻² day⁻¹) in shelf waters corresponding to the northern side of the western transect was as high as in the marginal ice zone (2.1 g C m⁻² day⁻¹), and was 4.8 times greater than that in open waters, suggesting that shelf waters are as highly productive as the marginal ice zone. A comparison between the historical productivity data and our data also shows that the most productive regions in the Southern Ocean are shelf waters and the marginal ice zone, with emerging evidence of frontal regions as another major productive site. Accepted: 27 September 1998     

Small nanoplankton and bacteria in the Western Ross Sea during sea-ice retreat (spring 1994)

Spatial changes of small nanoplankton (2–10 μm) were investigated in relation to sea-ice conditions, hydrography and receding ice processes in the Ross Sea (Antarctica) during spring 1994. Abundance and biomass of heterotrophic and autotrophic nanoplankton, as well as bacterioplankton, were determined along a south-north transect from the open waters polynya towards the pack ice. Autotrophic and heterotrophic nanoplankton biomass ranged from 758 to 4570 mgC m⁻² and from 3 to 387 mgC m⁻², respectively. Heterotrophic nanoplankton accounted, on average, for about 9% of the total (i.e. autotrophic plus heterotrophic) nanoplankton biomass. The size structure of both auto- and heterotrophic nanoplankton in the Ross Sea continental shelf receding ice edge was different from that of nanoplankton associated with the shelf break and open Antarctic ice-edge area. Generally, the highest heterotrophic biomass was found in the pack-ice zone on the continental shelf, while the highest heterotrophic contribution to the total nanoplankton biomass (up to 25%) was encountered at the shelf break where phytoplankton was largely dominated by 2- to 3-μm-size cells. Accepted: 2 May 1999     

Meiobenthic stocks and benthic activity on the NE-Svalbard shelf and in the Nansen Basin

Summary High Arctic meiofaunal distribution, standing stock, sediment chemistry and benthic respiratory activity (determined by sediment oxygen consumption using a shipboard technique) were studied in summer 1980 on the NE Svalbard shelf (northern Barents Sea) and along a transect into the Nansen Basin, over a depth range of 240–3920 m. Particulate sediment proteins, carbohydrates and adenylates were measured as additional measures of benthic biomass. To estimate the sedimentation potential of primary organic matter, sediment bound chloroplastic pigments (chlorophylls, pheopigments) were assayed. Pigment concentrations were found comparable to values in sediments from the boreal and temperate N-Atlantic. Meiofauna, which was abundant on the shelf, decreased in numbers and biomasses with increasing depth, as did sediment proteins, carbohydrates, adenylates and sediment oxygen consumption. Meiofaunal abundances and biomasses within the Nansen Basin were comparable with those observed in abyssal sediments of the North Atlantic. Nematodes clearly dominated in metazoan meiofauna. Protozoans were abundant in shelf sediments. Probably in response to the sedimentation of the plankton bloom, meiofauna abundance and biomass as well as sediment proteins, carbohydrates and adenylates were significantly correlated to the amount of sediment bound chloroplastic pigments, stressing the importance of food quantity to determine benthic stocks. Ninety-four percent of the variance in sediment oxygen consumption were caused by chloroplastic pigments. Benthic respiration, calculated per unit biomass, was 3–10 times lower than in the East Atlantic, suggesting low turnover rates in combination with a high standing stocks for the high Arctic benthos.     

Abundance, biomass and small-scale distribution of cryopelagic amphipods in the Franz Josef Land area (Arctic)

Arctic sea ice is inhabited by several amphipod species. Abundance, biomass and small-scale distribution of these cryopelagic (=ice associated) amphipods were investigated near Franz Josef Land in summer 1994. The mean abundance of all species was 420 ind./m²; the mean biomass was 10.61 g ww/m². Gammarus wilkitzkii was the dominant species, whereas Apherusa glacialis, Onisimus nanseni and O. glacialis were only scarcely found. Amphipods were concentrated at the edges of ice floes and were less frequent in areas further away under the ice. The relationship between the distribution and ecological/physiological requirements of cryopelagic amphipods, as well as the small-scale morphology of Arctic sea ice, are discussed. Received: 14 January 1998 / Accepted 14 April 1998     

Arctic cyanobacteria and limnological properties of their environment: Bylot Island, Northwest Territories, Canada (73°N, 80°W)

Cyanobacteria were a major constituent of phototrophic communities in the lakes, ponds and streams of Bylot Island, in the Canadian high Arctic. The waters spanned a range of temperatures (1.8–16.8°C in late July), pH regimes (6.2–9.2) and conductivities (1.5–1700 μS cm⁻¹) but nutrient concentrations were consistently low (< 1 μg dissolved reactive P l⁻¹ at all sites; < 10 μg NO₃-N l⁻¹ at most sites). Picoplanktonic species (Synechococcus spp.) were often the numerical dominants in the plankton, and periphytic filamentous species (Oscillatoriaceae) commonly formed thick (5–50 mm) benthic mats. Bloom-forming species of cyanobacteria were either absent or poorly represented even in Chla-rich ponds. The total community biomass ranged from 0.1 to 29.8 μg Chla l⁻¹ in the plankton and from 1.1 to 34.8 μg Chla cm⁻² in the benthos. The in vivo absorbance characteristics of isolates from these environments indicated a genetically diverse range of species in each group of Arctic cyanobacteria. Growth versus irradiance relationships were determined for each of the isolates and similarly revealed large genetic differences (maximum growth rates from 0.17 to 0.61 day⁻¹), even between morphologically identical taxa. A comparison of nutrients, pigment concentrations and species composition underscores the strong similarities between freshwater ecosystems in the north and south polar zones. Received: 3 June 1996 / Accepted: 3 November 1996     

Structure, above-ground biomass and dynamics of mangrove ecosystems: new data from French Guiana

The article presents new results on the structure and the above-ground biomass of the various population types of mangroves in French Guiana. Nine mangrove stands were studied, each composed of three to ten adjoining plots with areas that varied depending on the density of the populations. Structural parameters and indices were calculated. Individuals representative of the three groups of taxa present were felled:Avicennia germinans (L) Stearn, Rhizophora spp., and Laguncularia racemosa (L) Gaertn. The trunks, branches and leaves were sorted and weighed separately. The biomass was obtained by determining the allometric relationships, the general equation selected being of the type y = a _o x ^a1, where the diameter (x) is the predictive variable. The total above-ground biomass varied from 31 t ha⁻¹ for the pioneer stages to 315 t ha⁻¹ for mature coastal mangroves, but with large variations depending on the structural characteristics at each site. The results place the Guianese mangroves among those with high biomass, although lower than those reported for Asia. Based on the relationships between structural parameters and standing biomass, in particular with the use of the “self-thinning rule”, population dynamics models are proposed. Received: 16 August 1996 / Accepted 17 January 1998     

Ice algal assemblages and vertical export of organic matter from sea ice in the Barents Sea and Nansen Basin (Arctic Ocean)

Algal communities and export of organic matter from sea ice were studied in the offshore marginal ice zone (MIZ) of the northern Barents Sea and Nansen Basin of the Arctic Ocean north of Svalbard by means of ice cores and short-term deployed sediment traps. The observations cover a total of ten stations within the drifting pack ice, visited over a period of 3 years during the period of ice melt in May and July. Maximum flux of particulate organic carbon and chlorophyll a from the ice at 1 m depth (1,537 mg C m⁻² per day and 20 mg Chl a m⁻² per day) exceeded the flux at 30 m by a factor of 2 during spring, a pattern that was reversed later in the season. Although diatoms dominated the ice-associated algal biomass, flagellates at times revealed similarly high biomass and typically dominated the exported algal carbon. Importance of flagellates to the vertical flux increased as melting progressed, whereas diatoms made the highest contribution during the early melting stage. High export of ice-derived organic matter and phytoplankton took place simultaneously in the offshore MIZ, likely as a consequence of ice drift dynamics and the mosaic structure of ice-covered and open water characteristic of this region.     

Macrofauna communities in the Amundsen Basin, at the Morris Jesup Rise and at the Yermak Plateau (Eurasian Arctic Ocean)

Macrofaunal communities of the western Eurasian Arctic Ocean were studied along a transect from the North Pole, across the Amundsen Basin and Gakkel Ridge towards the Morris Jesup Rise and the Yermak Plateau. Samples were collected during autumn 1991, from depths of 560–4411 m, using a box corer. Macrofaunal species numbers varied from 1 to 11 per 0.02 m² in the basins approaching the Morris Jesup Rise and from 44 to 81 per 0.25 m² at the Yermak Plateau. Abundances increased from 1 to 31 per 0.02 m² in the basin and on the Morris Jesup Rise to 24–60 per 0.02 m² on the Yermak Plateau. Biomass was low in the basin and at the Morris Jesup Rise (0.5–68.9 mg per 0.02 m²) but increased to 116.64 mg per 0.02 m² at the Yermak Plateau. A total of 108 taxa were recorded. The results contradict the hypothesis that diversity decreases with increasing latitude, and the high species richness at low abundance at intermediate depths was comparable with that observed in Antarctic and tropical regions.     

The sub-ice fauna of the Laptev Sea and the adjacent Arctic Ocean in summer 1995

The sub-ice habitat and fauna in the Laptev Sea and the adjacent Arctic Ocean were investigated during the “Polarstern” cruise ARK XI/1 in summer 1995. At the ice-water interface a thin thermo- and halocline developed at many stations due to melting processes. In the lower centi- to decimetres of the ice, an accumulation of organic matter was found (particulate organic carbon: 1.9 mg l⁻¹, chl a: 3.3 μg l⁻¹) that may have provided a food source for the fauna. The water layer directly beneath the ice was inhabited by high numbers of various nauplii (130–23911 ind. m⁻³), and two ecological groups, the pelagic sub-ice fauna that originates from the surface water plankton, and the sympagic sub-ice fauna that migrates into this boundary layer from the ice interior. The pelagic fauna dominated the sub-ice community both in terms of species number and abundance. Both groups mainly comprised small copepods (e.g. Oithona similis, Oncaea borealis, Pseudocalanus spp., Halectinosoma spp., Tisbe spp.), but foraminifers and pteropods, for example, also occurred regularly. Diversity was generally low. Factors influencing the composition and abundance of the sub-ice fauna were most likely water depth, salinity and sea-ice sediments. Accepted: 6 July 1998     

Zooplankton communities of the Arctic’s Canada Basin: the contribution by smaller taxa

Zooplankton was sampled at ten stations in the Canada Basin during August 2002 using both 53- and 236-m mesh nets to examine the contribution by smaller and less studied species. Copepod nauplii, the copepods Oithona similis, Oncaea borealis and Microcalanus pygmaeus, and the larvacean Fritillaria borealis typica dominated the upper 100 m of the water column numerically, while biomass was dominated by the copepods Calanus hyperboreus, Calanus glacialis and Paraeuchaeta glacialis, and the chaetognath Eukrohnia hamata. Zooplankton biomass ranged from 3.7 to 14.5 mg AFDW m^–3, with a mean of 9.6 mg AFDW m^–3 . While the three microcopepods contributed less than 5% of the biomass, estimates of their potential growth rates suggest they might contribute upwards of 25% of the metazoan zooplankton production. The true rates of growth and development of these microcopepods in the Arctic need to be determined to conclusively ascertain their importance.