Lipids and trophic interactions of ice fauna and pelagic zooplankton in the marginal ice zone of the Barents Sea

Gammarus wilkitzkii, Apherusa glacialis, Onismus nanseni, Onismus glacialis, Boreogadus saida, Parathemisto libellula and Calanus hyperboreus, collected in late June in the Barents Sea marginal ice zone, contained substantial levels (28–51% of the dry mass) of total lipid, the highest levels (51% and 41% respectively) being in  A. glacialis and  C. hyperboreus. Neutral lipids were present in greater amounts than polar lipids in all species. Triacylglycerols were major neutral lipids in A. glacialis, G. wilkitzkii and O. nanseni; triacylglycerols and wax esters were present in similar amounts in O. glacialis; higher levels of wax esters than triacylglycerols occurred in P. libellula; wax esters greatly exceeded triacylglycerols in C. hyperboreus, the opposite being true for B. saida. Diatom fatty acid markers were prominent in the triacylglycerols of G. wilkitzkii, O. nanseni, O. glacialis and, particularly, of  A. glacialis; 20:1(n-9) and 22:1(n-11) moieties were abundant in wax esters of G. wilkitzkii, O. nanseni, O. glacialis, P. libellula and  C. hyperboreus, and in triacylglycerols of B. saida. We deduce that  A. glacialis feeds mainly on ice algae and phytodetritus, G. wilkitzkii and the Onismus spp. feed on calanoid copepods as well as ice algae, whereas P. libellula and especially B. saida feed extensively on calanoid copepods. Accepted: 17 May 1998     

Chick diet of dovekies Alle alle in Northwest Greenland

This paper reports the results of an investigation of dovekies (Alle alle) breeding at Hakluyt Island in the Thule District, Northwest Greenland. The paper presents a comprehensive examination of the chick diet of dovekies in the species' most important breeding area. Food delivered to nestlings consisted primarily of copepods Calanus hyperboreus and C. glacialis in the copepodite stages IV and V. Themisto libellula, other amphipods, decapods and fish larvae in small numbers were found in the chick diet. The zooplankton in the chick diet is presented both in terms of numbers and dry weight. The characteristic copepod of high-arctic waters, C. hyperboreus, was found to be the single most important species in the chick diet, contributing approximately 54% of the dry food weight. The food samples revealed low diversity, and the three species C. hyperboreus, C. glacialis and T. libellula made up 91.5% of the total zooplankton dry weight. The results from this paper are compared with previous dovekie-chick diet studies. Accepted: 14 June 2000     

Osmotic responses to hyposmotic stress in the amphipods Gammarus wilkitzkii,Onisimus glacialis and Parathemisto libellula from Arctic waters

Summary The amphipods Gammarus wilkitzkii and Onisimus glacialis, which commonly occur in burrows and pockets or near the bottom of the Arctic sea-ice, are euryhaline osmoregulators, displaying regulation of haemolymph concentrations of sodium and chloride. O. glacialis is the most efficient regulator. The amphipod Parathemisto libellula, which seems restricted to the subice fauna, is a stenohaline osmoconformer with no ability to regulate haemolymph concentrations of sodium and chloride. Thus, the physiological measurements made support the observed micro-distribution of the amphipods in relation to the Arctic sea ice.     

Zooplankton boom and ice amphipod bust below melting sea ice in the Amundsen Gulf, Arctic Canada

Early summer in the Arctic with extensive ice melt and break-up represents a dramatic change for sympagic–pelagic fauna below seasonal sea ice. As part of the International Polar Year-Circumpolar Flaw Lead system study (IPY-CFL), this investigation quantified zooplankton in the meltwater layer below landfast ice and remaining ice fauna below melting ice during June (2008) in Franklin Bay and Darnley Bay, Amundsen Gulf, Canada. The ice was in a state of advanced melt, with fully developed melt ponds. Intense melting resulted in a 0.3- to 0.5-m-thick meltwater layer below the ice, with a strong halocline to the Arctic water below. Zooplankton under the ice, in and below the meltwater layer, was sampled by SCUBA divers. Dense concentrations (max. 1,400 ind. m⁻³) of Calanus glacialis were associated with the meltwater layer, with dominant copepodid stages CIV and CV and high abundance of nauplii. Less abundant species included Pseudocalanus spp., Oithona similis and C. hyperboreus. The copepods were likely feeding on phytoplankton (0.5–2.3 mg Chl-a m⁻³) in the meltwater layer. Ice amphipods were present at low abundance (<10 ind. m⁻²) and wet biomass (<0.2 g m⁻²). Onisimus glacialis and Apherusa glacialis made up 64 and 51% of the total ice faunal abundance in Darnley Bay and Franklin Bay, respectively. During early summer, the autochthonous ice fauna becomes gradually replaced by allochthonous zooplankton, with an abundance boom near the meltwater layer. The ice amphipod bust occurs during late stages of melting and break-up, when their sympagic habitat is diminished then lost.     

Ice amphipod distribution relative to ice density and under-ice topography in the northern Barents Sea

Arctic ice amphipods are part of the sympagic macrofauna in the Marginal Ice Zone of the northern Barents Sea and represent an important link from lower to higher trophic levels in some Arctic marine food chains. The species diversity in this area (1995/1996) consisted of four species: Gammarus wilkitzkii, Apherusa glacialis, Onisimus nanseni and Onisimus glacialis. The larger ice amphipod, G. wilkitzkii, was the most abundant with the highest biomass (>90%), whereas A. glacialis was abundant, but contributed little to the total biomass (<4%). The other two species were found only in small numbers. Both abundance and biomass of ice amphipods decreased along a latitudinal gradient from north to south across the Marginal Ice Zone. Their distribution was also related to the under-ice topography with regard to mesoscale structures (edge, flat area, dome and ridge). Overall, the abundance and biomass on ridges were much higher in comparison to other mesoscale structures, although edges also showed high abundance, but low biomass. The large G. wilkitzkii was consistently abundant on ridges. The small A. glacialis was predominately associated with edges, but also showed high numbers in dome-shaped areas. The Onisimus species were present in low numbers at all structures, and their biomass contributed <10% on any one structure. The reasons for different distribution patterns of the dominant amphipod species under Arctic sea ice are probably related to different requirements of the species, especially for food, shelter and physiological conditions. Accepted: 27 November 1999     

Seabird species associations and affinities to areas covered with sea ice in the northern Greenland and Barents Seas

Species associations and affinity to sea ice among arctic marine birds were studied during ship transects in the northern Greenland and Barents Seas in the period 1980–1984. Associations were investigated at the scale of visual contact, and the sampling units were 10-min periods, corresponding to a transect length of 1.5–3 km. In the Greenland Sea, three or four of the most abundant species, fulmar (Fulmarus glacialis), little auk (Alle alle), Brünnich's guillemot (Uria lomvia) and kittiwake Rissa tridactyla, composed a recurrent group in all years. In the Barents Sea, fulmars, Brünnich's guillemots and kittiwakes were most often clustered. A positive association with sea ice was found in more than one cruise in three seabird species: black guillemots, ivory gulls and little auks, whereas seven other species showed negative association with ice in more than one cruise. The observed species associations and affinities to sea ice reflect similarities in diet among the species involved. Received: 23 February 1994 / Accepted: 12 January 1997     

Feeding, respiration and life history of the hyperiid amphipod Themisto libellula in the Arctic marginal ice zone of the Greenland Sea

Daily ingestion rates of the pelagic hyperiid amphipod Themisto libellula were studied in the marginal ice zone of the Arctic Fram Strait by feeding experiments, respiration measurements and an allometric approach based on body mass. Amphipods were collected by stratified multiple opening/closing net hauls and Rectangular Midwater Trawl (RMT 8) in August 2000 during the expedition ARK XVI/2 of R/V “Polarstern”. T. libellula occurred with abundances of 0.043 and 0.015 ind. m⁻³ in the upper 30 m of the water column at two RMT 8 stations. Based on respiration data, the daily ingestion necessary to cover metabolic energy demands measured 1.9±0.6% of body carbon per day. Actual prey consumption during feeding experiments with Calanus copepodids as prey was very similar and accounted for 1.9±1.5% day⁻¹, indicating that feeding on Calanus can meet the energy demands of T. libellula. In general, experimental results were slightly lower than the maximum potential ingestion (2% day⁻¹ for an individual of median body dry mass of 32 mg) estimated by an allometric equation based on body mass, but feeding experiments showed a strong variability. Reduced metabolism and low ingestion rates of T. libellula are consistent with low ambient temperature, large body size, slow growth and long life span of this polar species. The effect of the active pelagic life style of T. libellula on metabolism and ingestion rate is discussed in comparison to the sympagic (i.e. ice-associated) amphipod Gammarus wilkitzkii of similar body size living in the same environment. In relation to the mesozooplankton biomass in the investigation area, the predation impact by T. libellula was low. However, high-Arctic conditions also limit the secondary production of principal prey species, such as Calanus glacialis and Calanus hyperboreus, so that even low predation rates may affect the growth of prey populations.     

Export or retention? Copepod abundance,faecal pellet production and vertical flux in the marginal ice zone through snap shots from the northern Barents Sea

The balance between faecal pellet (FP) production and destruction that accelerates or diminishes vertical export has an effect on pelagic-benthic coupling, but is inadequately known. Production, export and retention of copepod FP were investigated in the marginal ice zone (MIZ) of the northern Barents Sea in July 2003. Older stages of Calanus finmarchicus and C. glacialis dominated the copepod biomass and FP production experiments revealed that more than 90% of the FP were produced in the upper 50 m where most of the copepods were located both day and night. Copepod pellets typically made up ∼10% of the vertical particulate organic carbon flux, and significantly less than what was produced by the copepod community. This implies a variable but significant retention of pellets. We suggest that retention of FP is caused partly by the zooplankton themselves and that retention of FP is the rule rather than the exception in the Barents Sea, particularly during non-bloom scenarios.     

Spatial distribution and life-cycle timing of zooplankton in the marginal ice zone of the Barents Sea during the summer melt season in 1995

The marginal ice zone (MIZ) in the northern Barents Sea is ecologically important because it represents a highly productive area in Arctic water masses north of the Polar Front. During a multi-disciplinary cruise in 1995, ecological and oceanographic processes were investigated at four stations located in a north-south transect in the MIZ. This study was carried out in Arctic water masses north of the Polar Front where ice conditions varied from dense first-year pack ice to open water. Also, the phytoplankton development varied along the transect from a pre-bloom situation at the northern-most station to a post-bloom situation in the open water. This paper includes a study of the zooplankton community and population structure of some of the dominant copepod species. Numerically, the most important mesozooplankton components were the copepods Calanus glacialis, Pseudocalanus minutus and Oithona similis. Copepods of Atlantic origin, such as Calanus finmarchicus and Oithona atlantica, gave evidence of an advection of Atlantic water masses into the area. It is concluded that the occurrence of new cohorts of Arctic copepods coincides with the onset of the phytoplankton bloom in the MIZ, and, that therefore, the spawning relies on stored energy.      

Is the poleward expansion by Atlantic cod and haddock threatening native polar cod, <Emphasis Type="Italic">Boreogadus saida</Emphasis>?

During a recent period of increased influx of warm Atlantic water to the western coast of Svalbard, we have observed a northward expansion of boreal Atlantic cod (Gadus morhua) and haddock (Melanogrammus aeglefinus) into areas dominated by the native polar cod (Boreogadus saida). To determine the potential impact of new ecological interactions, we studied the diet of co-occurring juvenile gadoids in fjords, open water, and sea ice around Svalbard. We also reviewed the available literature on polar cod feeding in different habitats across the Arctic to determine whether region, habitat, or fish size may influence diet. Feeding by polar cod in the pelagic zone was size dependent, with small fish primarily consuming Calanus spp. and smaller copepods, with an increasing ration of Themisto spp. at larger sizes. In benthic habitats, diets were more varied and included considerably more unidentified material and sediment. Less than 40% dietary overlap was detected among the three species when they were found together. Stable isotope analyses indicated these patterns were representative of longer-term assimilation. The low interspecific dietary overlap suggests little direct competition. Future increases in abundance and the high predation potential of the boreal taxa, however, may impact the persistence of polar cod on some Arctic shelves.     

Seasonal changes in zooplankton composition in the Barents Sea, with special attention to Calanus spp. (Copepoda)

The Barents Sea is an important area with respect to fisheriesresources (i.e. capelin and cod). In May, June and August 1981zooplankton biomass was measured along a transect at 30°E,from the ice border southwards. A maximum was recorded in Atlanticwater by the end of June (>100 g wet weight m^–2 InAugust the biomass values were relatively low south of the Polarfront and increased northwards into Arctic water (–50g m^–2 The species composition was influenced by the distributionof cold Arctic water and warmer Atlantic water. The zooplanktonwas dominated by the copepods Calanus finmarchicus and C. glacialis;the former is regarded as an Atlantic species and C. glacialisas an Arctic species.     

Arctic sea ice as feeding ground for amphipods – food sources and strategies

The amphipod species Gammarus wilkitzkii, Apherusa glacialis, Onisimus nanseni and O. glacialis live permanently associated with the Arctic sea ice. Qualitative and semi-quantitative investigations of gut contents and faeces showed that all four species use detritus as the main food source. Detrital lumps from the underside of sea ice had the same item composition as amphipod gut contents and faeces. Crustacean remains and ice algae were additional food items, but overall they were quantitatively less important. All species are omnivorous; however, differences in gut contents, behavioural observations and functional–morphological studies of the mandibles suggest a differentiation within this feeding strategy. G. wilkitzkii is a detritivorous-carnivorous-necrophagous-suspension-feeding species and shows the most complex feeding strategy. O. nanseni and O. glacialis are predominantly detritivorous-necrophagous, whereas A. glacialis is characterised as a more herbivorous-detritivorous species. By using a variety of the available food sources under Arctic sea ice, the amphipods are well adapted to the under-ice habitat and are less influenced by temporal and spatial variations. Furthermore, the wide food spectrum of all four species reduces the intra- and interspecific competition in a habitat where certain food sources are limited or only seasonally available. Accepted: 30 June 2000     

Feeding habits of harp seals (Phoca groenlandica) during early summer and autumn in the northern Barents Sea

The feeding habits of harp seals (Phoca groenlandica) in the Barents Sea were examined in studies conducted during June 1991, September 1990 and 1991, and October 1992. Analyses of stomach and intestinal contents were carried out and concurrent estimates of prey abundance were made using trawl gear. Harp seals appeared to feed at low intensity in the pack ice belt during the first half of June. There was little potential prey in the water column, but prawns (Pandalus borealis), capelin (Mallotus villosus) and polar cod (Boreogadus saida) were abundant close to the bottom. In September, the seals sampled in the northern pack ice areas of the Barents Sea fed on the pelagic amphipod Parathemisto libellula, krill (Thysanoessa spp.), prawns and, to a lesser extent, on fish species such as polar cod, sculpins (Cottidae) and snailfish (Liparidae). Trawling revealed that large quantities of Parathemisto libellala were present in the upper layers of the water column. Fish, mainly capelin and polar cod, were less abundant and occurred in deeper waters. In mid-October, the diet of seals in the northern Barents Sea consisted mainly of amphipods (Parathemisto sp.). Later in October, when increasing pack ice cover forced the harp seals to move south, the diet seemed to change from amphipods to fish prey, predominantly capelin and polar cod.     

Distribution and diet of demersal Arctic Cod, <Emphasis Type="Italic">Boreogadus saida</Emphasis>, in relation to habitat characteristics in the Canadian Beaufort Sea

Arctic Cod (Boreogadus saida) occur throughout the circumpolar north; however, their distributions at localized scales are not well understood. The seasonal habitat associations and diet preferences across life-history stages of this keystone species are also poorly known, thereby impeding effective regulatory efforts in support of conservation objectives. The distribution of Arctic Cod in the Canadian Beaufort Sea was assessed using bottom trawling in shelf and slope habitats between 20 and 1000 m depths. Highest catch biomasses occurred at 350 and 500 m depth slope stations, coinciding with >0 °C temperatures in the Pacific–Atlantic thermohalocline and Atlantic water mass. Calanus glacialis, Calanus hyperboreus, Themisto libellula, and Themisto abyssorum were identified as key prey species in the diet of Arctic Cod, comprising approximately 86 % of total biomass in guts. Hierarchical cluster analysis with a SIMPROF test identified five statistically significant (p < 0.05) diet groups among gut samples. Arctic Cod shifted from a primarily Calanus diet at shelf stations (<200 m depth) to a Themisto diet in slope habitats (>200 m depth) coinciding with an associated increase in fish standard length with depth. Smaller Arctic Cod fed primarily on Calanus copepods and larger Arctic Cod fed primarily on the larger Themisto species. The habitat and diet associations presented here will inform knowledge of structural and functional relationships in Arctic marine ecosystems, aid in mitigation and conservation efforts, and will enhance our ability to predict the effects of climate change on the local spatial and depth associations of this pivotal marine fish.     

Lipid composition of copepodite stages and adult females of Calanus glacialis in Arctic waters of the Barents Sea

Summary The composition of lipid classes and their component fatty acid are described for copepodite stages III, IV, V, and adult females of Calanus glacialis sampled from Arctic waters of the Barents Sea during summer. Was esters were the principal component of the lipid in all copepodite stages examined, averaging 73% over all the stages. The proportion of triacylglycerols varied from 1.5% to 10.5% of total lipid among copepodite stages. The lipids of adult females contained lower levels of wax esters and higher levels of triacylglycerols than copepodite stages III, IV and V. Fatty alcohols of wax esters from copepods sampled in June and July were dominated by 20:1 (n-9) and 22:1 (n-11) alcohols with the proportion of 20:1 (n-9) increasing from stages III to adult female. 14:0 and 16:0 alcohols were the principal fatty alcohols of wax esters of a sample comprising mainly of copepodites stage III taken in August. 16:1 (n-7), 20:1 (n-9) and 20:5 (n-3) were the major fatty acids in the was esters of animals captured in June and July whereas 18:1 (n-9) predominated in the August sample. The polar lipids of the copepodite stage III from August also contained lower levels of polyunsaturated fatty acids than from all stages of copepods from June and July. The data are discussed in relation to life cycle strategies and trophic aspects of Calanus glacialis in the Arctic pelagic community of the Barents Sea.     

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     

Molecular relationships of gammaridean amphipods from Arctic sea ice

The information on the biology and ecology of the Arctic sea ice-associated amphipods (Apherusa glacialis, Gammarus wilkitzkii, Onisimus glacialis, and O. nanseni) has increased, but their molecular taxonomic information still remains undisclosed. In the present study, we investigated long-range DNA sequences spanning 18S to 28S rDNA of these four sea ice-associated amphipods and analyzed their genetic relationships with other amphipod taxa. Variations of rDNA within the individuals of the same species were not detected. Phylogenetic analyses showed that each ice amphipod was separated, forming clusters with other conspecifics. Pairwise comparisons led to similar phylogenetic results, showing that the molecular taxonomy of the ice amphipods was in accordance with morphological systematics. In addition, these findings suggest that all four amphipods have little genetic variation compared with their morphologically defined conspecifics from temperate regions. Based on DNA taxonomy, G. wilkitzkii was supported as a species in good standing, refuting a recent synonymization with Gammarus duebeni. Considerably low genetic divergences of O. glacialis and O. nanseni in 18S, ITS, and 28S rDNA suggest the presence of population distinctions within species.     

Distribution and diet of 0-group cod (<Emphasis Type="Italic">Gadus morhua</Emphasis>) and haddock (<Emphasis Type="Italic">Melanogrammus aeglefinus</Emphasis>) in the Barents Sea in relation to food availability and temperature

Distribution of 0-group cod (Gadus morhua) and haddock (Melanogrammus aeglefinus) in August–September 2005 and 2006 was mainly restricted to the Atlantic waters of the western and central areas of the Barents Sea. The main distribution of 0-group fish overlapped largely with areas of high biomass (>7 gm⁻² dry weight) of zooplankton. The copepod Calanus finmarchicus and krill Thysanoessa inermis, which are dominant zooplankton species in both Atlantic and boreal waters of the Barents Sea, were the main prey of 0-group cod and haddock. The main distribution, feeding areas and prey of 0-group cod and haddock overlapped, implying that competition for food may occur between the two species. However, though their diet coincided to a certain degree, haddock seems to prefer smaller and less mobile prey, such as Limacina and appendicularians. As 0-group fish increased in size, there seems to be a shift in diet, from small copepods and towards larger prey such as krill and fish. Overall, a largely pelagic feeding behaviour of 0-group cod and haddock was evident from this study.     

Feeding of <Emphasis Type="Italic">Themisto libellula</Emphasis> (Amphipoda Crustacea) on natural copepods assemblages in an Arctic fjord (Kongsfjorden,Svalbard)

Ingestion rates and selectivity of the Arctic pelagic amphipod Themisto libellula were studied experimentally in Kongsfjorden (Svalbard, 78°N) during the summer period. Feeding incubations were conducted on naturally occurring copepod communities at different concentrations ranging from 25 to 250 preys L⁻¹. The ingestion rates increased with food availability from 1.3 to 17.7 preys ind⁻¹ day⁻¹, which corresponded to 0.3–11% of body carbon day⁻¹. Despite the high prey concentration used in the experiments the satiation level was not reached. We suggested that T. libellula is able to take the maximum benefit from dense patches of preys, which represent a good adaptation to the high variability in food supply characteristic of polar environment. Copepodids stage III of Calanus spp. appeared to be the preferred preys of T. libellula. Smaller copepods such as Oithona similis and Pseudocalanus spp., were also selected but only when their relative abundance exceeded 25% of the total prey available. The potential predation impact of T. libellula is discussed in relation to the mesozooplankton small-scale patchiness and predator abundance.