Distribution patterns of benthic microalgal standing stock at McMurdo Sound,Antarctica

Summary During the austral summer of 1975–76 and winter of 1977 benthic and water column chlorophyll a and phaeopigments were measured at several sites along the east and west sides of McMurdo Sound, Antarctica. Estimates of in situ primary productivity were made at some McMurdo Sound locations. Additionally, water column samples were collected at 5 stations in the Ross Sea during January, 1976. Standing stock data are analyzed to identify seasonal and spatial patterns. Variability in algal standing stock was related to ambient light levels and appeared to be mediated by ice and snow cover whereby the highest algal standing stock was present under high light conditions (low ice and snow cover, shallow water, summer). Differences in published benthic invertebrate densities appear to be closely allied to differences in benthic primary production, and less so to in situ planktonic ice microalgal production.     

Species size distributions in Arctic benthic communities

In most subtidal soft-sediment faunal assemblages there is a trough in the species size distribution separating the macrofauna and meiofauna. To examine the hypothesis that this may be maintained by the avoidance of competition between macrofaunal adults and settling larvae, samples were taken from around Svalbard, an area where most macrofaunal species have either lecithotrophic or direct development. At three contrasting sites, bimodality of the species size spectrum was conserved. However, it is proposed that the adult-larval interaction hypothesis should not be rejected as low endemism in the fauna of the study area suggests its species size spectrum probably reflects evolutionary processes outside rather than within the Arctic. Received: 13 May 1996/Accepted: 26 July 1996     

Zonation in the deep benthic megafauna

A test based on Maxwell-Boltzman statistics, instead of the formerly suggested but inappropriate Bose-Einstein statistics (Pielou and Routledge, 1976), examines the distribution of the boundaries of species' ranges distributed along a gradient, and indicates whether they are random or clustered (zoned). The test is most useful as a preliminary to the application of more instructive but less statistically rigorous methods such as cluster analysis. The test indicates zonation is marked in the deep benthic megafauna living between 200 and 3000 m, but below 3000 m little zonation may be found.     

Competition between ammonia-oxidizing bacteria and benthic microalgae

The abundance, activity, and diversity of ammonia-oxidizing bacteria (AOB) were studied in prepared microcosms with and without microphytobenthic activity. In the microcosm without alga activity, both AOB abundance, estimated by real-time PCR, and potential nitrification increased during the course of the experiment. AOB present in the oxic zone of these sediments were able to fully exploit their nitrification potential because NH(4)(+) did not limit growth. In contrast, AOB in the alga-colonized sediments reached less than 20% of their potential activity, suggesting starvation of cells. Starvation resulted in a decrease with time in the abundance of AOB as well as in nitrification potential. This decrease was correlated with an increase in alga biomass, suggesting competitive exclusion of AOB by microalgae. Induction of N limitation in the oxic zone of the alga-colonized sediments and O(2) limitation of the majority of AOB in darkness were major mechanisms by which microalgae suppressed the growth and survival of AOB. The competition pressure from the algae seemed to act on the entire population of AOB, as no differences were observed by denaturing gradient gel electrophoresis of amoA fragments during the course of the experiment. Enumeration of bacteria based on 16S rRNA gene copies and d-amino acids suggested that the algae also affected other bacterial groups negatively. Our data indicate that direct competitive interaction takes place between algae and AOB and that benthic algae are superior competitors because they have higher N uptake rates and grow faster than AOB.     

Indirect Interactions in the High Arctic

Indirect interactions as mediated by higher and lower trophic levels have been advanced as key forces structuring herbivorous arthropod communities around the globe. Here, we present a first quantification of the interaction structure of a herbivore-centered food web from the High Arctic. Targeting the Lepidoptera of Northeast Greenland, we introduce generalized overlap indices as a novel tool for comparing different types of indirect interactions. First, we quantify the scope for top-down-up interactions as the probability that a herbivore attacking plant species i itself fed as a larva on species j. Second, we gauge this herbivore overlap against the potential for bottom-up-down interactions, quantified as the probability that a parasitoid attacking herbivore species i itself developed as a larva on species j. Third, we assess the impact of interactions with other food web modules, by extending the core web around the key herbivore Sympistis nigrita to other predator guilds (birds and spiders). We find the host specificity of both herbivores and parasitoids to be variable, with broad generalists occurring in both trophic layers. Indirect links through shared resources and through shared natural enemies both emerge as forces with a potential for shaping the herbivore community. The structure of the host-parasitoid submodule of the food web suggests scope for classic apparent competition. Yet, based on predation experiments, we estimate that birds kill as many (8%) larvae of S. nigrita as do parasitoids (8%), and that spiders kill many more (38%). Interactions between these predator guilds may result in further complexities. Our results caution against broad generalizations from studies of limited food web modules, and show the potential for interactions within and between guilds of extended webs. They also add a data point from the northernmost insect communities on Earth, and describe the baseline structure of a food web facing imminent climate change.     

Behavioural responses of benthic and pelagic Arctic charr to substratum heterogeneity

Responses to environmental heterogeneity were studied in laboratory-reared offspring of two morphs of Arctic charr Salvelinus alpinus from Loch Rannoch, Scotland, one occupying the pelagic zone and feeding predominantly on zooplankton and the other being benthic in habit and feeding mainly on macroinvertebrates. When housed in groups in tanks with a black-and white striped base, benthic charr demonstrated a clear preference for dark areas, whereas pelagic fish positioned themselves at random with respect to substratum colour. In general, pelagic charr were much less aggressive than benthic charr. In pelagic fish, neither spacing nor aggression was affected by the visual heterogeneity of the substrate. In contrast, benthic charr swam closer together and fought more when housed over a uniform as opposed to a non-uniform substratum. The results are discussed in the context of habitat-specific visual requirements and of an interaction between visual complexity and territoriality previously described for Atlantic salmon Salmo salar .     

Degradation and recovery of an Arctic benthic community under organic enrichment

Fast development of mariculture in the world leads to increasing of the load on natural habitats, especially due to organic enrichment. There are a few investigations concerning the effect of additional organic loading on the Arctic benthic communities. The main goal of our research was to ascertain the impact of mussel farm on the benthic community in the White Sea and its following recovery after mussel farm removal. We performed annual observations from 1988 to 2011. During the mussel farm functioning, two stages of organic enrichment impact on community structure were recorded: in the first 2 years, diversity and proportion of deposit feeders increased but later all studied characteristics of the benthic community decreased significantly. After the mussel farm removal, the benthic community started to restore and we distinguished several stages of recovery succession. Native structure of benthic community began to recover 8 years after organic loading had ceased, when selective deposit feeding bivalves Portlandia arctica Gray appeared in the benthos. 4–6 years later it became the only dominating species in the studied benthic community. Therefore, in the White Sea, native structure recovery of the Arctic benthic community after the severe disturbance took about 15 years.     

Diversity and characterization of mercury-resistant bacteria in snow, freshwater and sea-ice brine from the High Arctic

It is well-established that atmospheric deposition transports mercury from lower latitudes to the Arctic. The role of bacteria in the dynamics of the deposited mercury, however, is unknown. We characterized mercury-resistant bacteria from High Arctic snow, freshwater and sea-ice brine. Bacterial densities were 9.4 × 10(5), 5 × 10(5) and 0.9-3.1 × 10(3) cells mL(-1) in freshwater, brine and snow, respectively. Highest cultivability was observed in snow (11.9%), followed by freshwater (0.3%) and brine (0.03%). In snow, the mercury-resistant bacteria accounted for up to 31% of the culturable bacteria, but <2% in freshwater and brine. The resistant bacteria belonged to the Alpha-, Beta- and Gammaproteobacteria, Firmicutes, Actinobacteria, and Bacteriodetes. Resistance levels of most isolates were not temperature dependent. Of the resistant isolates, 25% reduced Hg(II) to Hg(0). No relation between resistance level, ability to reduce Hg(II) and phylogenetic group was observed. An estimation of the potential bacterial reduction of Hg(II) in snow suggested that it was important in the deeper snow layers where light attenuation inhibited photoreduction. Thus, by reducing Hg(II) to Hg(0), mercury-resistant bacteria may limit the supply of substrate for methylation processes and, hence, contribute to lowering the risk that methylmercury is being incorporated into the Arctic food chains.     

Spring-to-summer changes and regional variability of benthic processes in the western Canadian Arctic

Seasonal dynamics in the activity of Arctic shelf benthos have been the subject of few local studies, and the pronounced among-site variability characterizing their results makes it difficult to upscale and generalize their conclusions. In a regional study encompassing five sites at 100–595 m water depth in the southeastern Beaufort Sea, we found that total pigment concentrations in surficial sediments, used as proxies of general food supply to the benthos, rose significantly after the transition from ice-covered conditions in spring (March–June 2008) to open-water conditions in summer (June–August 2008), whereas sediment Chl a concentrations, typical markers of fresh food input, did not. Macrobenthic biomass (including agglutinated foraminifera >500 μm) varied significantly among sites (1.2–6.4 g C m⁻² in spring, 1.1–12.6 g C m⁻² in summer), whereas a general spring-to-summer increase was not detected. Benthic carbon remineralisation also ranged significantly among sites (11.9–33.2 mg C m⁻² day⁻¹ in spring, 11.6–44.4 mg C m⁻² day⁻¹ in summer) and did in addition exhibit a general significant increase from spring-to-summer. Multiple regression analysis suggests that in both spring and summer, sediment Chl a concentration is the prime determinant of benthic carbon remineralisation, but other factors have a significant secondary influence, such as foraminiferan biomass (negative in both seasons), water depth (in spring) and infaunal biomass (in summer). Our findings indicate the importance of the combined and dynamic effects of food supply and benthic community patterns on the carbon remineralisation of the polar shelf benthos in seasonally ice-covered seas.     

Radiolaria: Sinking population,standing stock,and production rate

A method is presented for estimating sinking population, rate of production, and residence time in the living zone for Radiolaria. This method employs vertical flux measurements from PARFLUX sediment traps and laboratory sinking speed measurements of the radiolarian skeletons.The estimated population sinking through the oceanic water column is approximately equal to the standing stock at several hundred meters depth reported from direct measurements by other workers. The rate of production of total Radiolaria was estimated to be approximately 80 shells m^?3 day^?1 in the western equatorial Atlantic (E) and central Pacific (P₁) stations and 230 shells m^?3 day^?1 in the Panama Basin (PB). The production of Nassellaria is greater than that of the other suborders. The average residence time for Radiolaria in the living zone (0–200 m) was estimated to be between 16 and 42 days.     

Enclosure experiment on the control mechanism of planktonic bacterial standing stock

In order to understand the control mechanisms of a large, stable bacterial standing stock, enclosure experiments were conducted in a eutrophic lake, where both bacterial productivity and grazing pressure were very high. Total bacterial number in the different enclosures ranged from 1.2 to 2.7×10⁷ cells mL⁻¹ throughout the experiment. The average bacterial cell production rate estimated from a grazer eliminating experiment was 6.3×10⁵ cells mL⁻¹ h⁻¹. Difference in the bacterial cell production rate between shaded and unshaded enclosures was not apparent. Bacteria showed a reduction in standing stock of only about 25–30% even after the supply of light was cut to 1%. Bacteria in the shaded enclosures then recovered their production rate in the first 12 days of perturbation. Grazing pressure in the shaded enclosures was not less than that for the control. Thus, it was considered a control mechanism of bacterial stable standing stock that the bacteria shifted their organic substrate from extracellular dissolved organic carbon freshly released from phytoplankton to that already stocked in the water column, though it is not known whether the dominant bacteria were the same.     

Bacterivory by benthic organisms in sediment: Quantification usingN-enriched bacteria

The fate of benthic bacterial biomass in benthic food webs is a topic of major importance but poorly described. This paper describes an alternative method for evaluation of bacterial grazing rate by meiofauna and macrofauna using bacteria pre-enriched with stable isotopes. Natural bacteria from the sediment of an intertidal mudflat were cultured in a liquid medium enriched with ¹⁵NH₄Cl. Cultured bacteria contained 2.9% of ¹⁵N and were enriched sufficiently to be used as tracers during grazing experiments. Cultured bacteria presented a biovolume (0.21 μm³) and a percentage of actively respiring bacteria (10%) similar to those found in natural communities. The number of Operational Taxon Units found in cultures fluctuated between 56 and 75% of that found in natural sediment. Despite this change in community composition, the bacterial consortium used for grazing experiments exhibited characteristics of size, activity and diversity more representative of the natural community than usually noticed in many other grazing studies. The bacterial ingestion rates of three different grazers were in the range of literature values resulting from other methods: 1149 ngC ind^− 1h^− 1 for the mud snail Hydrobia ulvae, 0.027 ngC ind^− 1 h^− 1 for the nematode community, and 0.067 ngC ind^− 1 h^− 1 for the foraminifera Ammonia tepida. The alternative method described in this paper overcomes some past limitations and it presents interesting advantages such as short time incubation and in situ potential utilisation.     

Regional patterns of nematode assemblages in the Arctic deep seas

Surface primary productivity and carbon flux in the Arctic Seas are higher along the warm Spitsbergen Water Current than along the ice-infested East Greenland Current. These contrasting oceanographic conditions are reflected in the deep-sea environment and may shape nematode assemblages. However, the paucity of samples in the Arctic deep seas precludes any regional scale assessment. In the present study, nematode assemblages were investigated in relation to a range of environmental variables along the 2,000 m isobath between latitudes 72°N and 79°N for both East and Western margins of the northern North Atlantic. Results showed that both margins had distinct environmental characteristics, with respect to chloroplastic pigments, sediment water content, sediment-bound organic matter, phospholipids and particulate proteins. Nematode assemblages varied according to these environmental changes. Along the more oligotrophic western margin, chloroplastic pigments increased towards the North, while the other environmental variables, nematode abundances and species richness decreased. In contrast, along the eastern margin, we observed higher quantities of organic matter and particulate protein, which supported higher abundance and species richness. Nematode assemblages along both margins varied according to food availability with species composition more variable in areas with lower amounts. Seventy percent of the species occurred in both margins indicating a low turnover of species. The present results support the hypothesis of a positive latitudinal gradient across the North Atlantic and further suggest that contemporary climate and recent ecological processes may predict nematode diversity patterns at larger scales.     

ROV observations of benthic fishes in the Northwind and Canada Basins, Arctic Ocean

Abyssal and midslope Arctic benthic fishes were sampled nonquantitatively by still photography and videography from a remotely operated vehicle (ROV) between 13 August and 7 September 2002. Species diversity was low: only six putative species were seen, including Lycodes frigidus Collett 1879, Lycodes sp., Rhodichthys regina Collett 1879, Paraliparis bathybius (Collett 1879), Raja (Amblyraja) hyperborea Collett 1879, and Cottunculus species diversity varied among stations sampled. An analysis of 1-min segments of videotape from one long ROV dive suggested that habitat selection by demersal nekton in these environments may be associated with the presence, absence, or density of other benthic animals.     

Diversity,cold active enzymes and adaptation strategies of bacteria inhabiting glacier cryoconite holes of High Arctic

Cryoconite holes have biogeochemical, ecological and biotechnological importance. This communication presents results on culturable psychrophilic bacterial diversity from cryoconite holes at Midre Lovénbreen (ML), Austre Brøggerbreen (AB), and Vestre Brøggerbreen (VB) glaciers. The culturable bacterial count ranged from 2.7 × 10³ to 8.8 × 10⁴ CFUs/g while the total bacterial numbers ranged from 5.07 × 10⁵ to 1.50 × 10⁶ cells at the three glaciers. A total of 35 morphologically distinct bacterial isolates were isolated. Based on 16S rRNA gene sequence data, the identified species belonged to eight genera namely Pseudomonas, Polaromonas, Micrococcus, Subtercola, Agreia, Leifsonia, Cryobacterium and Flavobacterium. The isolates varied in their growth temperature, NaCl tolerance, growth pH, enzyme activities, carbon utilization and antibiotic sensitivity tests. Fatty acid profiles indicate the predominance of branched fatty acids in the isolates. To the best of our knowledge, this is the first record of culturable bacterial communities and their characterization from glacier cryoconites from High Arctic. High amylase and protease activities expressed by Micrococcus sp. MLB-41 and amylase, protease and lipase activities expressed by Cryobacterium sp. MLB-32 provide a clue to the potential applications of these organisms. These cold-adapted enzymes may provide an opportunity for the prospect of biotechnology in Arctic.     

Carbonate standing stock and carbonate production of the bryozoanPentapora fascialis in the North-Western Mediterranean

Summary Pentapora fascialis, one of the largest living bryozoan, is often a predominant part of the benthos on hard subtidal bottoms in the Mediterranean Sea. Conversion factors calculated from laboratory measurements of colony size, biomass and skeleton weight, combined with density of colonies and mean annual growth rate allowed the estimation of carbonate standing stock, biomass and carbonate production ofPentapora fascialis in five sites in the Ligurian Sea. Carbonate standing stock ranged from 281 to 2490 g·m⁻², colony biomass varied from 8.82 to 78.01 g·m⁻², with a ratio biomass to carbonate standing stock of about 3%. Carbonate production of the bryozoan ranged in the five sites from 358 to 1214 g·m⁻²·y⁻¹. If compared with the few data available on carbonate production of bryozoans and other sublittoral benthic bioconstructors in the temperate regions,Pentapora fascialis has to be considered one of the major contributors to the carbonatebudget.