Impact of warm water advection on the winter zooplankton community in an Arctic fjord

The west coast of Spitsbergen is influenced by water masses of Atlantic and Arctic origin. During the winter of January–April 2006, water temperatures on the West Spitsbergen Shelf were ∼3°C warmer than typical winter conditions, leading to a coastal sea ice cover of reduced thickness, extent and duration. A sediment trap deployed from September 2005 to May 2006 in the outer basin of Kongsfjorden (NW Spitsbergen) at a depth of 115 m has provided a continuous winter time-series of zooplankton during a period of rapid increase in water temperatures. Prior to an anomalous and prolonged influx of warm Atlantic water (AW) starting at the end of January, the trap samples were dominated by the boreo-Arctic copepod Metridia longa. Species that increased in abundance during the influx included late stages of Calanus finmarchicus, C. glacialis, C. hyperboreus and Paraeuchaeta norvegica. The early introduction of shelf populations into the fjord, and thus increased copepod biomass relative to typical winter conditions with little advection, has implications for the marine pelagic food web and pelagic-benthic coupling.     

Intra- and interspecific differences in palatability of Arctic macroalgae from Kongsfjorden (Spitsbergen) for two benthic sympatric invertebrates

Information on herbivore-macroalgae interactions is extremely scarce for Arctic habitats. In this study, the potential of 19 macroalgae as food source for herbivores was investigated for the first time in Arctic waters (Kongsfjorden, Spitsbergen) with emphasis on algal defense against grazing. Only two of the 19 tested macroalgae-associated invertebrates consumed macroalgae in measurable amounts, the locally abundant green sea urchin Strongylocentrotus droebachiensis (OF Müller) and the amphipod Gammarellus homari (JC Fabricius). In the inner basin of the fjord, the dense macroalgal stock represents a potential food source. However, in this area, herbivory plays only a minor role. In contrast, in the outer basin of Kongsfjorden S. droebachiensis exerts a strong top-down control on macroalgal assemblages.Laboratory feeding assays in the with the two herbivores showed grazer-specific feeding preferences. The amphipod G. homari exhibits a preference for delicate red algal species like Devaleraea ramentacea, whereas the sea urchin S. droebachiensis significantly preferred more leathery seaweeds like Laminaria and Alaria. The red alga Palmaria palmata is a very attractive food for both herbivores, while the brown alga Desmarestia viridis and the red alga Ptilota gunneri are among the least preferred algae. To distinguish between physical and tissue-specific plant properties, which have a deterring or stimulating effect on the grazing behaviour, both grazers were offered intact algal tissue and artificial food in separate feeding assays. While physical and tissue-specific plant properties-especially in the Laminariales-deterred G. homari, these properties did not deter S. droebachiensis.This study provides insights into herbivore consumption in the benthic food web of Kongsfjorden. As a general potential top-down factor controlling primary production, herbivory needs to be quantified further in Kongsfjorden to develop adequate carbon flow models for this important reference site for the study of climate change on high latitude marine ecosystems.     

Seasonal and individual variability of lipid reserves in <Emphasis Type="Italic">Oithona similis</Emphasis> (Cyclopoida) in an Arctic fjord

The lipid storage of the cyclopoid copepod Oithona similis was investigated from spring to late summer 2007 in Kongsfjorden (Svalbard, Norway). The volume of lipid droplets in each individual reflected the amount of stored wax esters. Seasonal changes of lipid storage coupled with informative inter-individual variability were thus obtained. The seasonal pattern showed an increase in lipid store during the spring bloom, starting before the chlorophyll a maximum for both copepodids stage V and females. Those reserves were used during the main reproductive event in June. Individual variability was very high, with a significant proportion of copepods having no droplet, while others were lipid rich. Because of the overlap of generation, females could have different age and feeding history, particularly in September. Consideration of intra-population variability in lipid storage using an optical approach has been shown to be important to understand O. similis’s ecology and life cycle.     

Do sulphuric acid and the brown alga <Emphasis Type="Italic">Desmarestia viridis</Emphasis> support community structure in Arctic kelp patches by altering grazing impact,distribution patterns,and behaviour of sea urchins?

Macrobenthic community structure and the distribution of the green sea urchin (Strongylocentrotus droebachiensis) were recorded inside and outside (=barrens) of kelp patches (Alaria esculenta) at Kongsfjordneset, Svalbard between August 2002 and October 2006. In manipulative field experiments, conducted at Kongsfjordneset, Svalbard in August 2002, the effect of the presence of the brown seaweed Desmarestia viridis on sea urchin distribution and kelp grazing was determined. Additionally, we studied the effect of sulphuric acid, which is produced and stored by D. viridis, on sea urchin movements in the laboratory at Ny-Ålesund, Svalbard, in May 2006. Sea urchin densities were two- to threefold lower in kelp patches than on barrens. The macrobenthic community inside kelp patches hosted 39% more species and was of different species composition than on barrens. Anchored pieces of the kelp A. esculenta were less consumed when surrounded by D. viridis than non-surrounded conspecifics. Changes in pH affected the behaviour of sea urchins. Exposing sea urchins to 500 μl seawater at pH 7.5 caused them to stop, while the exposure of as little as 25 μl at pH 1 caused sea urchins to move in the opposite direction. Acid-mediated escape responses in sea urchin behaviour suggest chemical protection by D. viridis as an additional mechanism to mechanical protection in the generation of kelp refuges. These results improve our understanding of how isolated kelp beds can persist over a wide range of environmental conditions, like wave-sheltered sites, and suggest that changes in community structure may be in part attributable to altered trophic interactions.     

The distribution of picoplankton and nanoplankton in Kongsfjorden,Svalbard during late summer 2006

Abundance and biomass of pico- (<2 μm) and nanoplankton (2–20 μm) were investigated in relation to hydrography in Kongsfjorden, Svalbard (79°N, 12°E) during late summer 2006. Autotrophic and heterotrophic picoplankton abundance ranged from 0.1 × 10⁶ to 35.2 × 10⁶ cells L⁻¹ and from 0.4 × 10⁶ to 20.3 × 10⁶ cells L⁻¹, respectively. The highest number of bacteria in the entire water column was recorded at station 2 at 10 m (22.3 × 10⁸ cells L⁻¹); the lowest concentration was observed at station 1 (6.0 × 10⁸ cells L⁻¹). The abundance of autotrophic and heterotrophic nanoplankton varied from 0.4 × 10⁵ cells L⁻¹ to 46 × 10⁵ cells L⁻¹ and from 0.3 × 10⁶ to 9.1 × 10⁶ cells L⁻¹, respectively. Our results demonstrated that heterotrophic nanoflagellates and bacteria in Kongsfjorden microbial community were relatively important. The structure of plankton communities integrated with environmental variables could act as indicators of the variability of the inflow of Atlantic Water into Kongsfjorden.     

Influence of glacial melt and Atlantic water on bacterioplankton community of Kongsfjorden,an Arctic fjord

The Kongsfjorden, an Arctic fjord is experiencing warming due to increased input of Atlantic water masses. High-throughput sequencing was performed to examine bacterial diversity from the outer and inner zone of the fjord in summer and fall of 2012. A total of 11,999 operational taxonomic units (OTUs) were assigned into 19 known phyla and 5 genera incertae sedis. Significant variation (p = 0.001, n = 4) was observed between the bacterial community structure of outer and inner fjord while variation between summer and fall was minimum. Proteobacteria was the most abundant phylum (55.9-61.0%) in summer and fall. The most dominant alphaproteobacterial member of this phylum (OTU 263 Pelagibacteriaceae) contributed maximum to the observed dissimilarity between the outer and inner fjord community. Characterised by relatively fresher and warmer water, glacial meltwater input could be a major source of predominance of OTU 6968 Flavobacteriaceae, OTU 5552 Psychrobacter, OTU 7148 Sphingomonadales and OTU 5011 Loktanella in the inner fjord in summer. Thus, the significant variation in the bacterioplankton community composition of outer and inner fjord indicates strong and localized influence of glacial melt water in shaping the community structure.