Trophic niches of macrobenthos: Latitudinal variation indicates climate change impact on ecosystem functioning.

Benthic food-web structure and organic matter (OM) utilization are important for marine ecosystem functioning. In response to environmental changes related to the ongoing climate change, however, many benthic species are shifting their ranges to colder regions, which may lead to altered community composition, but it remains largely unknown how it will affect ecosystem functioning. Here, stable isotope analysis was used to study benthic OM utilization and food-web structure and to assess whether their spatial patterns reflect today's community differentiation among biogeographic regions and depth zones. Benthic fauna and OM mixtures were collected from two depth zones (100-150 m vs. 200-250 m) within a temperate, two sub-Arctic, and an Arctic fjord along a latitudinal gradient (59-78° N) that was used as a space-for-time substitution to assess the impact of climate change. Our results showed that Arctic and temperate communities are functionally different. Arctic communities were characterized by a strong resource partitioning among different feeding types, irrespective of depth zone. In contrast, all feeding types in temperate communities seemed to rely on sedimentary OM. The sub-Arctic presented a transition zone. In the sub-Arctic, shallower communities resembled Arctic communities, suggesting a functional transition between temperate and sub-Arctic regions. Deeper sub-Arctic communities resembled temperate communities, suggesting a functional transition between the sub-Arctic and Arctic regions. This implies that the regions north of the current transitions (deep Arctic and shallow sub-Arctic) are most likely to experience functional changes related to an altered OM utilization in benthic food webs in response to climate change.

Biodiversity: the overlooked source of human health.

Biodiversity is the measure of the variation of lifeforms in a given ecological system. Biodiversity provides ecosystems with the robustness, stability, and resilience that sustains them. This is ultimately essential for our survival because we depend on the services that natural ecosystems provide (food, fresh water, air, climate, and medicine). Despite this, human activity is driving an unprecedented rate of biodiversity decline, which may jeopardize the life-support systems of the planet if no urgent action is taken. In this article we show why biodiversity is essential for human health. We raise our case and focus on the biomedicine services that are enabled by biodiversity, and we present known and novel approaches to promote biodiversity conservation.

Nematode responses to an Arctic sea-ice regime: morphometric characteristics and biomass size spectra.

Body size is one of the most important traits of organisms that affects their behavioral life histories, physiologies, and energy requirements. For sediment-dwelling organisms, such as free-living nematodes, body size is a direct adaptation for living in sediments with a particular particle size, but other environmental factors, e.g., water depth and food availability, directly or indirectly shape nematode morphology. Nevertheless, our knowledge of meiofaunal organisms sizes still lags far behind that of other aquatic fauna, particularly for high-latitude fauna. Therefore, to gain insight into the nematode community size structure, we investigated eight stations located in the seasonal sea-ice zone north of Svalbard (Yermak Plateau, Nansen Basin, and Northern Svalbard shelf) during Arctic spring. Sample locations covered a wide depth gradient, different sea-ice concentrations and subsequent bloom stages. Our study provides previously unavailable data on nematode morphometry for this Arctic region during ecologically important spring to summer transition times. We analyzed nematode biomass, body shape and morphometric attributes, along with respective feeding types and life stage information. Our results show that differences in nematode densities, biomass and allometric attributes most likely reflect differences in the flux of organic material to the seafloor and in the biogeochemical properties of the sediments. Nematode assemblages appeared to respond to spatial gradients in ice cover duration and therefore pelagic productivity from the northern Svalbard shelf to the Yermak Plateau as evidenced by decreasing density, biomass and body size. Considering the entire community, as well as different life stages, average individual body weight decreased northward. Biomass dominance in the lower weight classes and the significantly lower abundance of long and thick morphotype nematodes observed on the Yermak Plateau than in the two other regions were striking. This was in contrast with the assemblage observed on the shelf, where prevailing environmental conditions influenced the presence of other morphotypes - markedly longer and wider organisms. Ongoing changes in sea-ice cover and primary production in the Arctic may significantly affect nematode functioning, as they are expected to have pronounced impacts on nematode morphological characteristics. In this regard, the size-based approach becomes a useful tool for detecting changes in the community and has important implications for predicting the direction of change with regard to benthic productivity.

Benthic phosphorus cycling within the Eurasian marginal sea ice zone.

The Arctic Ocean region is currently undergoing dramatic changes, which will likely alter the nutrient cycles that underpin Arctic marine ecosystems. Phosphate is a key limiting nutrient for marine life but gaps in our understanding of the Arctic phosphorus (P) cycle persist. In this study, we investigate the benthic burial and recycling of phosphorus using sediments and pore waters from the Eurasian Arctic margin, including the Barents Sea slope and the Yermak Plateau. Our results highlight that P is generally lost from sediments with depth during organic matter respiration. On the Yermak Plateau, remobilization of P results in a diffusive flux of P to the seafloor of between 96 and 261 µmol m-2 yr-1. On the Barents Sea slope, diffusive fluxes of P are much larger (1736-2449 µmol m-2 yr-1), but these fluxes are into near-surface sediments rather than to the bottom waters. The difference in cycling on the Barents Sea slope is controlled by higher fluxes of fresh organic matter and active iron cycling. As changes in primary productivity, ocean circulation and glacial melt continue, benthic P cycling is likely to be altered with implications for P imported into the Arctic Ocean Basin. This article is part of the theme issue 'The changing Arctic Ocean: consequences for biological communities, biogeochemical processes and ecosystem functioning'.

Benthic macrofaunal bioturbation activities from shelf to deep basin in spring to summer transition in the Arctic Ocean.

The aim of this study was to assess bioturbation rates in relation to macrozoobenthos and environmental variables in the Svalbard fjords, Barents Sea and Nansen Basin during spring to summer transition. The results showed differences in benthic community structure across sampled area in relation to sediment type and phytopigment content. Fjords, Barents Sea and the shallow parts of Nansen Basin (<400 m) were characterized by high functional groups diversity, and by biodiffusive and non-local rates ranging from 0.05 to 1.75 cm-2 y-1 and from 0.2 to 3.2 y-1, respectively. The deeper parts of Nansen Basin (>400m), dominated by conveyors species, showed only non-local transport rates (0.1-1 y-1). Both coefficients intensity varied with benthic biomass. Non-local transport increased with species richness and density and at stations with mud enriched by fresh phytopigments, whereas biodiffusion varied with sediment type and organic matter quantity. This study quantified for the first time the two modes of sediment mixing in the Arctic, each of which being driven by different environmental and biological situations.

Unexpected Levels of Biological Activity during the Polar Night Offer New Perspectives on a Warming Arctic.

The current understanding of Arctic ecosystems is deeply rooted in the classical view of a bottom-up controlled system with strong physical forcing and seasonality in primary-production regimes. Consequently, the Arctic polar night is commonly disregarded as a time of year when biological activities are reduced to a minimum due to a reduced food supply. Here, based upon a multidisciplinary ecosystem-scale study from the polar night at 79°N, we present an entirely different view. Instead of an ecosystem that has entered a resting state, we document a system with high activity levels and biological interactions across most trophic levels. In some habitats, biological diversity and presence of juvenile stages were elevated in winter months compared to the more productive and sunlit periods. Ultimately, our results suggest a different perspective regarding ecosystem function that will be of importance for future environmental management and decision making, especially at a time when Arctic regions are experiencing accelerated environmental change [1].

Low virus to prokaryote ratios in the cold: benthic viruses and prokaryotes in a subpolar marine ecosystem (Hornsund, Svalbard).

The density and spatial distribution of benthic viruses and prokaryotes in relation to biotic and abiotic factors were investigated in sediment cores collected in Hornsund, a permanently cold fjord on the West coast of Svalbard, Norway. The cores were obtained from the mouth of the fjord to the central basin, along a longitudinal transect. The results of our analyses showed lower densities of viruses (0.2 x 10(8) to 5.4 x 10(8) virus-like particles/g) and lower virus-to-prokaryote ratios (0.2-0.6, with the exception of the uppermost layer in the central basin, where the ratio was about 1.2) at the study site than generally found in the temperate areas, despite the relatively high organic matter content in subpolar sediments. Variations in benthic viral and prokaryote abundances along gradients of particle sedimentation rates, phytopigment concentrations, and macrobenthic species composition together suggested the influence of particle sedimentation and macrobenthic bioturbation on the abundance and spatial distribution ofprokaryotes and viruses in cold habitats.

Low virus to prokaryote ratios in the cold: benthic viruses and prokaryotes in a subpolar marine ecosystem (Hornsund, Svalbard)

The density and spatial distribution of benthic viruses and prokaryotes in relation to biotic and abiotic factors were investigated in sediment cores collected in Hornsund, a permanently cold fjord on the West coast of Svalbard, Norway. The cores were obtained from the mouth of the fjord to the central basin, along a longitudinal transect. The results of our analyses showed lower densities of viruses (0.2 x 10(8) to 5.4 x 10(8) virus-like particles/g) and lower virus-to-prokaryote ratios (0.2-0.6, with the exception of the uppermost layer in the central basin, where the ratio was about 1.2) at the study site than generally found in the temperate areas, despite the relatively high organic matter content in subpolar sediments. Variations in benthic viral and prokaryote abundances along gradients of particle sedimentation rates, phytopigment concentrations, and macrobenthic species composition together suggested the influence of particle sedimentation and macrobenthic bioturbation on the abundance and spatial distribution ofprokaryotes and viruses in cold habitats (AU)

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Benthic community structure, diversity, and productivity in the shallow Barents Sea bank (Svalbard Bank).

The Barents Sea is among the most productive areas in the world oceans, and its shallow banks exhibit particularly high rates of primary productivity reaching over 300 g C m-2year-1. Our study focused on the Svalbard Bank, an important feeding area for fishes and whales. In order to investigate how benthic community structure and benthic secondary production vary across environmental gradients and through time, we sampled across the bank and compared results with a similar study conducted 85 years ago. Considerable variability in community structure and function across bank corresponded with differences in the physical structure of the habitat, including currents, sedimentation regimes and sediment type, and overlying water masses. Despite an intensive scallop fishery and climatic shifts that have taken place since the last survey in the 1920s, benthic community structure was very similar to that from the previous survey, suggesting strong system resilience. Primary and secondary production over shallow banks plays a large role in the Barents Sea and may act as a carbon subsidy to surrounding fish populations, of which many are of commercial importance.