Seasonal distribution of sympagic amphipods near Chesterfield Inlet, N.W.T., Canada

The seasonal distribution of sympagic amphipods was investigated in the Chesterfield Inlet area of northwestern Hudson Bay (63°30′N). Amphipod abundance was measured by photographic samples and species composition was determined by sweep net samples. Twelve species of amphipods were collected, the most common being Ischyrocerus anguipes, Pontogeneia inermis, Apherusa megalops and Weyprechtia pinguis. The major environmental variable affecting amphipod distribution was water depth. Amphipod abundance was highest near 20 m and near zero past 50 m. The maximum recorded abundance was 1367 m⁻². A minor factor affecting the distribution of amphipods was snow depth, through its modifying effect on light and thereby the growth of ice algae. Amphipods began to inhabit the sea ice shortly after its formation. From the beginning of March, the number of amphipods on the ice increased steadily to about the 3rd week of April, after which numbers declined. This pattern coincided with the seasonal ice algae abundance. Amphipods reduced ice algal biomass over 20-m depth by 63%. No evidence of diurnal changes in abundance was observed. Received: 15 May 1996 / Accepted: 4 November 1996     

The diversity,abundance and fate of ice algae and phytoplankton in the Bering Sea

Despite being an essential part of the marine food web during periods of ice cover, sea ice algae have not been studied in any detail in the Bering Sea. In this study, we investigated the diversity, abundance and ultimate fate of ice algae in the Bering Sea using sea ice, water and sub-ice sediment trap samples collected during two spring periods in 2008 and 2009: ice growth (March–mid-April) and ice melt (mid-April–May). The total ice algal species inventory included 68 species, dominated by typical Arctic ice algal diatom taxa. Only three species were determined from the water samples; we interpret the strong overlap in species as seeding of algal cells from the sea ice. Algal abundances in the ice exceeded 10⁷ cells l^?1 in the bottom 2-cm layer and were on average three orders of magnitude higher than in the water column. The vertical flux of algal cells beneath the ice during the period of ice melt (>10⁸ cells m^?2 day^?1) exceeded export during the ice growth period by one order of magnitude; the vertical flux during both periods can only be sustained by the release of algae from the ice. Differences in the relative species proportions of algae among sample types indicated that the fate of the released ice algae was species specific, with some taxa contributing to seeding in the water column, while other taxa were preferentially exported.     

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     

Algae, macrofaunal assemblages and temperature: a quantitative approach to intertidal ecosystems of Iceland

Algae and the associated macrofauna in two Icelandic intertidal ecosystems under cold and warm influence, respectively, were studied with respect to algae-macrofauna relationships and a possible effect of temperature on community structure. Two sites in Iceland were selected, Sandgerdi ligthhouse (64°8′N 22°40′W) on the southwestern coast, and Grimsey Island (66°33′N 18°04′W), in the north, on the Arctic Circle, where sea temperature is considerably lower (5° approximately). The biomass of algae and the number of species of algae and macrofauna were higher in Sandgerdi than in Grimsey, and the patterns of diversity, evenness, biomass and abundance also differed between the sites. In the intertidal zone of Sandgerdi, a total of 28 species of algae and 45 species of macrofauna were identified whereas only 16 algal species and 27 macrofaunal species were found in Grimsey. Canonical correspondence analysis (CCA) using algal biomass as the environmental variable were conducted, and revealed significant relationships between algae composition and the associated macrofauna; some macrofauna taxa showed specific trophic or refuge relationships with algal species. According to the CCA, Corallina officinalis showed the highest correlation with macrofaunal assemblages in both study sites. However, correlations between macrofauna and other algae differed between Grimsey and Sandgerdi. The present study, together with additional observations in Greenland waters, shows a general decrease of species richness and diversity towards the north which may primarily be due to the temperature regime.     

Comparison of bottom sea-ice algal characteristics from coastal and offshore regions in the Arctic Ocean

Ice-core observations were conducted at three arctic sites in early April 2003: one clean sediment-free site (Chukchi), one sediment-rich site (Beaufort) on landfast sea ice offshore Barrow, and one oceanic Ice Exercise (ICEX) site. Concentrations of inorganic nutrients at coastal sites were similar to but higher than those at the oceanic site. Chlorophyll-a (Chl-a) concentration was much higher in the Chukchi bottom ice than at the other two sites. However, large size Chl-a (>20 μm) dominated (>70%) the bottom-ice algal Chl-a at both the Chukchi and Beaufort sites, whereas the oceanic ICEX site was evenly occupied by large (>20 μm), medium (5–20 μm), and small Chl-a (0.7–5 μm). These in situ data were incorporated into an ocean-ecosystem model. The model results revealed that: (1) strong light attenuation by trapped sediments controlled ice-algal production at the Beaufort site; (2) the peak in ice algae occurred later at the oceanic site than at the Chukchi site because of thicker ice and the consequently reduced amount of light reaching the ice algae at the ice bottom; and (3) maximum production at the oceanic site reached only 10% the level at the Chukchi site because of nutrient limitation.     

Ice algae during EPOS,leg 1: assemblages,biomass, origin and nutrients

Summary Ice algae in infiltration assemblages were the dominating primary producers in the northwestern Weddell Sea during the austral spring 1988. Band and sub-ice assemblages were encountered at a few stations only. Maximum ice algal biomass measured was 424 g Chl. a I^–1 compared to less than 0.4, g Chl. a I^–1 in the water column. Biomass and nutrient concentrations in the infiltration layer decreased inward from the edge of ice floes. The composition of algal groups indicated that the concentric distribution was due to migration by mobile taxa. Various procedures for melting of ice-containing samples of algae were tested. Melting in dialysis tubing seemed to have advantages over other methods, especially for cells to be used in physiological experiments.Data presented here were collected during the European Polarstern Study (EPOS) sponsored by the European Science Foundation     

Temporal and spatial variation of the phytoplankton assemblage in the eastern Indian sector of the Southern Ocean in summer 2001/2002

The abundance and species composition of phytoplankton were investigated at stations in a permanently ice-free (61°S) and seasonally ice-covered area (64°S and 66°30′S) in the eastern Indian sector of the Southern Ocean between November 2001 and March 2002. Although a phytoplankton bloom occurred just after retreat of the sea ice at both stations in the seasonally ice-covered area, vertical stability of the water column during the bloom was weak at the most southerly station. This shows that a bloom can form even under weak vertical stability. In the bloom, diatoms dominated under weak vertical stability and Phaeocystis under strong vertical stability. In the latter case, ice algae largely contributed to development of the bloom. In the later observation period, a subsurface chlorophyll maximum (SCM) was observed at 61°S and 64°S. Species composition was different between the mixed layer and SCM at 64°S, but was uniform with depth at 61°S, indicating that the SCM is formed by different mechanisms.     

The occurrence of sub-ice algal aggregations off northeast Greenland

Massive growth of sub-ice algal assemblages was recorded at two stations under first-year ice off northeast Greenland using a Remotely Operated Vehicle equipped with cameras. The assemblages mainly consisted of the diatom Melosira arctica (Ehr.) Dickie. A station sampled at the beginning of June 1993 revealed two forms of growth, curtain-like and rope-like, but with many intermediate types along the entire 150 m transect. The algal distribution was patchy. No significant sympagic fauna was found close to the algal masses. At a station sampled in the middle of July, similar algal concentrations seemed to be disturbed by ice-melting processes. Two casts under multi-year ice flows failed to show any algal aggregations. The observation of algal assemblages under first-year ice is in contrast to earlier reports from the Barents Sea where they have been recorded exclusively under multi-year ice.     

Verbreitung von Makrozooplankton in der Grönlandsee im Spätherbst 1988 (Crustacea: Ostracoda, Hyperiidea [Amphipoda], Euphausiacea)

The horizontal and vertical distribution and the abundance of ostracods, hyperiids (amphipods) and euphausiids in the Greenland Sea along a transect parallel 74°45′N (from 15°45′E to 08°30′W) are described. The samples were taken by RV “Meteor” in late autumn of 1988. 8 species of the above named groups have been recorded in two different water masses which were touched by the transect. 5 stations were situated in the realm of the Atlantic waters of the Spitsbergen Current. HereDiscoconchoecia elegans, Meganyctiphanes norvegica, andThemisto compressa are indicators for the southern Atlantic water. 6 stations belong to the Arctic area dominated by Arctic Surface Water, whereBoroecia borealis, Themisto abyssorum, Thysanoessa longicaudata, andThysanoessa inermis are quite abundant as borealsubarctic species, whereasThemisto libellula is a true species of pure Arctic water.

---

---

Mitarbeiterin der Taxonomischen Arbeitsgruppe an der Biologischen Anstalt Helgoland     

Monitoring and manipulation of a sublittoral hard bottom biocoenosis in Balsfjord,northern Norway

Sublittoral hard bottom biocoenoses in Balsfjord, Norway (69°31′ N, 19°1′ E), were monitored using underwater stereophotogrammetry. The study includes manipulation of natural densities of organisms and testing the importance of biological interactions and “key species ” for the structure of biocoenoses. Underwater photography has the advantages of being a non-destructive method, but it is selective because small or hidden organisms cannot always be observed. Field experiments with exclusion of organisms from cages seem suitable for testing hypotheses concerning which animals are “key species ” in certain biocoenoses. Sea-urchins(Strongylocentrotus droebachiensis, S. pallidus) were suspected to be “key species ” in the present study, and their removal from cages caused an increase in abundance of barnacles(Balanus balanoides), the limpetAcmaea testudinalis and algal cover.     

Biogeochemistry and microbial community composition in sea ice and underlying seawater off East Antarctica during early spring

Pack ice, brines and seawaters were sampled in October 2003 in the East Antarctic sector to investigate the structure of the microbial communities (algae, bacteria and protozoa) in relation to the associated physico-chemical conditions (ice structure, temperature, salinity, inorganic nutrients, chlorophyll a and organic matter). Ice cover ranged between 0.3 and 0.8 m, composed of granular and columnar ice. The brine volume fractions sharply increased above −4°C in the bottom ice, coinciding with an important increase of algal biomass (up to 3.9 mg C l⁻¹), suggesting a control of the algae growth by the space availability at that period of time. Large accumulation of NH₄ ⁺ and PO₄ ³⁻ was observed in the bottom ice. The high pool of organic matter, especially of transparent exopolymeric particles, likely led to nutrients retention and limitation of the protozoa grazing pressure, inducing therefore an algal accumulation. In contrast, the heterotrophs dominated in the underlying seawaters.     

Community structure and functional roles of meiofauna in the North Sea

Knowiedge on community structure of North Sea meiofauna has greatly increased recently. A quasisynoptic picture of meiofauna densities and copepod community structure from 171 stations of the southern North Sea, sampled in April–May 1986, has been obtained during the North Sea Benthos Survey. Latitudinal patterns in meiofauna abundance and copepod weight, abundance and diversity exist in an area between 51°30′N and 58°30′N. Using TWINSPAN-classification five major groups of copepod species can be recognized which are related to sediment type, latitude and depth. The part of the meiofauna in total benthic energy flow, their role in the benthic food web and in biogeochemical cycles is discussed based on existing literature. There are still considerable gaps in knowledge and the field is not progressing rapidly. Publication no. 599 Netherlands Institute of Ecology, Centre for Estuarine and Coastal Ecology, Yerseke, The Netherlands.     

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     

Microorganisms in a high altitude Glacier Ice in Tibet

Eighty-one strains of viable microorganisms were recovered from 23 samples collected from Ice Core 3 of Malan Glacier (China, 91° 45.3′ E, 35° 48.4′ N) drilled at high altitude (5620 m). All the strains were prokaryotes—75 of bacteria (including spore-forming ones) and 6 of actinomycetes. The characteristic genera differ from those of Arctic and Antarctic ice, in which many fungi and algae are widely distributed; this shows an difference of environmental conditions between Tibet and polar regions. The variation in number and species ofBacillus in different ice core layers implied changes of environmental conditions in the past.     

Effects of snow removal and algal photoacclimation on growth and export of ice algae

Net growth of ice algae in response to changes in overlying snow cover was studied after manipulating snow thickness on land-fast, Arctic sea ice. Parallel laboratory experiments measured the effect of changing irradiance on growth rate of the ice diatom, Nitzschia frigida. After complete removal of thick snow (≥9 cm), in situ ice algae biomass declined (over 7–12 days), while removal of thin snow layers (4–5 cm), or partial snow removal, increased net algal growth. Ice bottom ablation sometimes followed snow removal, but did not always result in net loss of algae. Similarly, in laboratory experiments, small increases in irradiance increased algal growth rate, while greater light shifts suppressed growth for 3–6 days. However, N. frigida could acclimate to relatively high irradiance (110 μmol photons m² s⁻¹). The results suggest that algal loss following removal of a thick snow layer was due to the combination of photoinhibition and bottom ablation. The smaller relative increase in irradiance after removal of thin or partial snow layers allowed algae to maintain high specific-growth rates that compensated for loss from physical mechanisms. Thus, the response of ice algae to snow loss depends both on the amount of change in snow depth and algal photophysiology. The complex response of ice algae growth and export loss to frequently changing snow fields may contribute to horizontal and temporal patchiness of ecologically and biogeochemically important variables in sea ice and should be considered in predictions of how climate change will affect Arctic marine ecosystems.     

Influence of sea ice on the composition of the spring phytoplankton bloom in the northern Baltic Sea

During the late winter and spring of 1994, the influence of sea ice on phytoplankton succession in the water was studied at a coastal station in the northern Baltic Sea. Ice cores were taken together with water samples from the underlying water and analysed for algal composition, chlorophyll a and nutrients. Sediment traps were placed under the ice and near the bottom, and the sedimented material was analysed for algal composition. The highest concentration of ice algae (4.1 mmol C m⁻²) was found shortly before ice break-up in the middle of April, coincidental with the onset of an under-ice phytoplankton bloom. The ice algae were dominated by the diatoms Chaetoceros wighamii Brightwell, Melosira arctica (Ehrenberg) Dickie and Nitzschia frigida Grunow. Under the ice the diatom Achnanthes taeniata Grunow and the dinoflagellate Peridiniella catenata (Levander) Balech were dominant. Calculations of sinking rates and residence times of the dominant ice algal species in the photic water column indicated that only one ice algal species (Chaetoceros wighamii) had a seeding effect on the water column: this diatom dominated the spring phytoplankton bloom in the water together with Achnanthes taeniata and Peridiniella catenata. Received: 9 May 1997 / Accepted: 15 February 1998     

High number of diatom species in first-year ice from the Chukchi Sea

Our study describes the species composition of microalgae, primarily diatoms, in two ice cores collected from the Chukchi Sea in early June 1998. At least 251 species were present in 2 cores collected 10 m apart in first-year ice. This is a greater number of algal species in ice from one locality than has been recorded from any other area of the Arctic. Microalgae were distributed throughout the 173-cm-long core, but abundance and species composition varied among different sections of the core, with maximum species richness (108 and 103 species in the 94- to 103- and 103- to 113-cm sections, respectively) occurring in the middle sections. More than 237 species were recorded from this core. Only the bottom 20 cm of the shorter (110 cm) core was analysed and it contained 135 algal species, still an extraordinarily high number of species. Marine species dominated both cores, but typical brackish and freshwater species were also present. None of these species, however, had more than 1% relative abundance. It should be noted, though, that there were several distinct, but unidentified, species of unknown origin. Characteristic ice algal species (e.g. Nitzschia frigida, Navicula pelagica, solitary Navicula spp., in addition to Cylindrotheca closterium) were the numerical dominants in most sections of the long core, but phytoplankton and benthic species were quite abundant in some sections. One section was dominated by a blue-green bacterium, presumably of the genus Anabaena. The species composition is consistent with several different mechanisms for algal incorporation into ice (i.e. seawater filtration ice, seeding from the sea floor, freshwater input). Over time, ice dynamics and sources of ice in the Chukchi Sea appear to result in high numbers of algal species in the ice. It is also likely that season of collection contributed to the high number of species observed. Determining the geographical area of origin for the different species is however difficult, due to the large-scale pattern of ice circulation.     

Sea ice primary productivity in the northern Barents Sea,spring 2004

The biomass and productivity of sea ice algae was assessed in the northwestern Barents Sea in May 2004. Sea ice algal pigment content was patchy with a mean of 18.5 ± 8.9 mg Chla m⁻². The algal community was dominated by the diatom Nitzschia frigida. Primary production measured by ¹⁴C incubations was between 0.37 and 2.8 mg C m⁻² h⁻¹, which compared well with oxygen-based methods using the diffusive boundary layer approach (0.071–1.1 mg C m⁻² h⁻¹). Given the differences in the irradiances under which these two sets of measurements were made, there was a strong level of consistency between the two sets of results. Measurements of primary production were consistent with previous Arctic measurements but high spatial heterogeneity made a regional estimate of production inappropriate.     

Possible spreading of toxic Alexandrium tamarense blooms on the Chukchi Sea shelf with the inflow of Pacific summer water due to climatic warming

A high abundance of resting cysts of the toxic dinoflagellate Alexandrium tamarense was recently reported in the vast continental shelf of the Chukchi Sea in the Arctic Ocean, suggesting that the species is widespread in the shelf. Nevertheless, little is known about the occurrence of A. tamarense vegetative cells in the water column of the arctic. Sea ice reduction and the inflow of Pacific summer water (PSW) through the Bering Strait have recently increased owing to warming in the shelf. To determine the spatial and temporal distributions of A. tamarense in the Chukchi Sea shelf and their relationship to the inflow of PSW, field samplings were conducted in the Chukchi Sea and north Bering Sea shelves three times during the summer of 2013 from July to October. Vegetative cells of A. tamarense was detected in both shelves at all sampling periods with a maximum density of 3.55 × 10³ cells L⁻¹. This species was also observed at the station at 73°N, indicating the northernmost record of this species to date. The center of the A. tamarense distribution was between the north Bering and south Chukchi Sea shelf during the first collection period, and spread to the north Chukchi Sea shelf during the second and third collection periods. The species occurrences were mainly observed at stations affected by the PSW, especially Bering shelf water. Water structure of PSW was characterized by warmer surface and bottom water temperatures, and increased temperatures may have promoted the cell growth and cyst germination of A. tamarense. Therefore, it is suggested that an increase in the PSW inflow owing to warming promotes toxic A. tamarense occurrences on the Chukchi Sea shelf.     

Year-to-year changes of the mesozooplankton community in the Chukchi Sea during summers of 1991, 1992 and 2007, 2008

A recent drastic decrease in sea ice cover area was observed in the western Arctic Ocean during summer, yet little information is available for its effect on zooplankton community. To evaluate the effect of sea ice reduction on zooplankton, we studied year-to-year changes of zooplankton community structure in the Chukchi Sea during summers of 1991, 1992 (when sea ice extended), 2007, and 2008 (when sea ice reduced). Zooplankton abundance ranged from 4,000 to 316,000 ind. m⁻² (mean: 70,000) and was greater north of Lisburne Peninsula in 2008. Zooplankton biomass ranged from 0.07 to 286 g wet mass m⁻² (mean: 36) and was greater south of Lisburne Peninsula in 2007. Cluster analysis based on zooplankton abundance showed a division of the zooplankton community into four groups. Occurrence of each group was separated geographically and interannually, and geographic distributions of each group in 1991 and 1992 were similar but those in 2007 and 2008 were shifted northward. Abundance and biomass in 2007/2008 were higher than in 1991/1992, indicating that further sea ice reduction would have a positive effect on zooplankton production (e.g. invasion of large Pacific species and temperature effects on their growth rate). The northern shift in geographic distribution of the zooplankton community in 2007/2008 indicates that sea ice reduction would have a negative effect on the zooplankton community (loss of characteristic Arctic species) in part of the Chukchi Sea. These apparently contradictory effects of sea ice reduction on zooplankton community emphasize the critical need for continued monitoring in this area.