Andrey V. Dolgov

Climate change alters the structure of arctic marine food webs due to poleward shifts of boreal generalists

Climate-driven poleward shifts, leading to changes in species composition and relative abundances, have been recently documented in the Arctic. Among the fastest moving species are boreal generalist fish which are expected to affect arctic marine food web structure and ecosystem functioning substantially. Here, we address structural changes at the food web level induced by poleward shifts via topological network analysis of highly resolved boreal and arctic food webs of the Barents Sea. We detected considerable differences in structural properties and link configuration between the boreal and the arctic food webs, the latter being more modular and less connected. We found that a main characteristic of the boreal fish moving poleward into the arctic region of the Barents Sea is high generalism, a property that increases connectance and reduces modularity in the arctic marine food web. Our results reveal that habitats form natural boundaries for food web modules, and that generalists play an important functional role in coupling pelagic and benthic modules. We posit that these habitat couplers have the potential to promote the transfer of energy and matter between habitats, but also the spread of pertubations, thereby changing arctic marine food web structure considerably with implications for ecosystem dynamics and functioning.

Demersal fish assemblages and spatial diversity patterns in the Arctic-Atlantic transition zone in the Barents Sea.

Direct and indirect effects of global warming are expected to be pronounced and fast in the Arctic, impacting terrestrial, freshwater and marine ecosystems. The Barents Sea is a high latitude shelf Sea and a boundary area between arctic and boreal faunas. These faunas are likely to respond differently to changes in climate. In addition, the Barents Sea is highly impacted by fisheries and other human activities. This strong human presence places great demands on scientific investigation and advisory capacity. In order to identify basic community structures against which future climate related or other human induced changes could be evaluated, we analyzed species composition and diversity of demersal fish in the Barents Sea. We found six main assemblages that were separated along depth and temperature gradients. There are indications that climate driven changes have already taken place, since boreal species were found in large parts of the Barents Sea shelf, including also the northern Arctic area. When modelling diversity as a function of depth and temperature, we found that two of the assemblages in the eastern Barents Sea showed lower diversity than expected from their depth and temperature. This is probably caused by low habitat complexity and the distance to the pool of boreal species in the western Barents Sea. In contrast coastal assemblages in south western Barents Sea and along Novaya Zemlya archipelago in the Eastern Barents Sea can be described as diversity “hotspots”; the South-western area had high density of species, abundance and biomass, and here some species have their northern distribution limit, whereas the Novaya Zemlya area has unique fauna of Arctic, coastal demersal fish. (see Information S1 for abstract in Russian).

Climate-driven changes in functional biogeography of Arctic marine fish communities

Significance Arctic marine ecosystems are experiencing a rapid biogeographic change following the highest warming rates observed around the globe in recent decades. Currently, there are no studies of how the observed shifts in species composition are affecting Arctic marine ecosystem functioning at a biogeographic scale. We address this issue via functional biogeography and show that increasing temperatures and reduced ice coverage are associated with the borealization of Arctic fish communities. We find that large body-sized piscivorous and semipelagic boreal species are replacing small-bodied benthivorous Arctic species, likely affecting biomass production in the benthic and pelagic compartments and their coupling. The documented speed and magnitude of climate-driven borealization will profoundly alter ecosystem functioning in the Arctic. Climate change triggers poleward shifts in species distribution leading to changes in biogeography. In the marine environment, fish respond quickly to warming, causing community-wide reorganizations, which result in profound changes in ecosystem functioning. Functional biogeography provides a framework to address how ecosystem functioning may be affected by climate change over large spatial scales. However, there are few studies on functional biogeography in the marine environment, and none in the Arctic, where climate-driven changes are most rapid and extensive. We investigated the impact of climate warming on the functional biogeography of the Barents Sea, which is characterized by a sharp zoogeographic divide separating boreal from Arctic species. Our unique dataset covered 52 fish species, 15 functional traits, and 3,660 stations sampled during the recent warming period. We found that the functional traits characterizing Arctic fish communities, mainly composed of small-sized bottom-dwelling benthivores, are being rapidly replaced by traits of incoming boreal species, particularly the larger, longer lived, and more piscivorous species. The changes in functional traits detected in the Arctic can be predicted based on the characteristics of species expected to undergo quick poleward shifts in response to warming. These are the large, generalist, motile species, such as cod and haddock. We show how functional biogeography can provide important insights into the relationship between species composition, diversity, ecosystem functioning, and environmental drivers. This represents invaluable knowledge in a period when communities and ecosystems experience rapid climate-driven changes across biogeographical regions.

Structure of the macroplankton–pelagic fish–cod trophic complex in a warmer Barents Sea

Abstract Long-term data indicate that climatic fluctuations in the Barents Sea can have significant impacts on populations of euphausiids, capelin and cod, but it is unclear how the current warming period in the area has altered trophic interactions among these taxa. The species composition and distribution of euphausiids; the abundance, distribution and feeding habits of capelin; and the feeding of cod on capelin and euphausiids were analysed. Data from the last decade suggest a shift in the spatial patterns and intensity of the euphausiid–capelin link, and a reduction in the volatility of population sizes of these species. Meanwhile, cod feeding has expanded farther to the north in the Barents Sea and may benefit from reduced fluctuations in prey availability. The reliability of advection of euphausiids into the region and the potential interactions with boreal species expanding into the Barents Sea, both of which are tightly coupled to climatic conditions, will determine how the pelagic ecosystem functions in the future.

Annotated list of fish-like vertebrates and fish of the Kara Sea

Based on literature and new actual data from 2007–2012, a revised list of fish species inhabiting the Kara Sea is given. The modern ichthyofauna of the Kara Sea comprises 77 species of marine, anadromous, and freshwater fish from 24 families of 14 orders. For the first time, 12 fish species are indicated for this region.

Climatic and ecological drivers of euphausiid community structure vary spatially in the Barents Sea: relationships from a long time series (1952–2009)

Euphausiids play an important role in transferring energy from ephemeral primary producers to fish, seabirds, and marine mammals in the Barents Sea ecosystem. Climatic impacts have been suggested to occur at all levels of the Barents Sea food-web, but adequate exploration of these phenomena on ecologically relevant spatial scales has not been integrated sufficiently. We used a time-series of euphausiid abundance data spanning 58 years, one of the longest biological time-series in the Arctic, to explore qualitative and quantitative relationships among climate, euphausiids, and their predators, and how these parameters vary spatially in the Barents Sea. We detected four main hydrographic regions, each with distinct patterns of interannual variability in euphausiid abundance and community structure. Assemblages varied primarily in the relative abundance of Thysanoessa inermis versus T. raschii, or T. inermis versus T. longicaudata and Meganyctiphanes norvegica. Climate proxies and the abundance of capelin or cod explained 30-60% of the variability in euphausiid abundance in each region. Climate also influenced patterns of variability in euphausiid community structure, but correlations were generally weaker. Advection of boreal euphausiid taxa from the Norwegian Sea is clearly more prominent in warmer years than in colder years, and interacts with seasonal fish migrations to help explain spatial differences in primary drivers of euphausiid community structure. Non-linear effects of predators were common, and must be considered more carefully if a mechanistic understanding of the ecosystem is to be achieved. Quantitative relationships among euphausiid abundance, climate proxies, and predator stock-sizes derived from these time series are valuable for ecological models being used to predict impacts of climate change on the Barents Sea ecosystem, and how the system should be managed.

Large-scale patterns in community structure of benthos and fish in the Barents Sea

Biogeographical patterns have an ecological basis, but few empirical studies possess the necessary scale and resolution relevant for investigation. The Barents Sea shelf provides an ideal study area, as it is a transition area between Atlantic and Arctic regions, and is sampled by a comprehensive survey of all major functional groups. We studied spatial variation in species composition of demersal fish and benthos to elucidate how fish and benthos communities co-varied in relation to environmental variables. We applied co-correspondence analysis on presence–absence data of 64 fishes and 302 benthos taxa from 329 bottom trawl hauls taken at the Barents Sea ecosystem survey in August–September 2011. We found highly significant similarities in the spatial pattern of distribution of benthos and fishes, despite their differences in motility and other ecological traits. The first common ordination axis separated boreal species in the south-west (Atlantic temperate water) from Arctic species in the north-east (Arctic cold water, ice-covered in winter). The second common axis separated shallow bank species from species found in deep basins and trenches. Our results show that fish and benthos communities had a similar relationship to the environmental gradients at the scale of hundreds to thousands of kilometres. We further discussed how fish–benthos interactions vary between sub-regions in the Barents Sea based on species traits and a food web topology for the Barents Sea. This study forms a basis for further investigations on links between fish and benthos communities in the Barents Sea.

Composition and Structure of the Mesopelagic Fish Communities in the Irminger Sea and Adjacent Waters

Species composition of ichthyofauna and the structure of the fish communities in the Irminger Sea and adjacent waters were studied in May–July 2003–2011. In total, 115 species/taxa have been registered in the catches; they belong to 47 families and 18 orders. The data on their abundance and biomass are presented. The vertical, spatial, and interannual variability of the species composition and the structure of ichthyocenosis have been described.

Observations of biota in Stepovogo Fjord, Novaya Zemlya, a former dumping site for radioactive waste

Stepovogo Fjord, located on the eastern coast of Novaya Zemlya, is an important former Soviet Union dumping site for radioactive waste. There is little information available on marine biota in this area. Better knowledge on the structure of marine food webs will allow for more accurate assessments of the consequences of any potential radioactive releases from the dumped waste. This article describes the occurrence, size and age distribution and diet of fish species collected in Stepovogo Fjord in 2012. The occurrence of macroalgae and other benthic species is also described. The fish fauna was dominated by the demersal fishes navaga (Eleginus nawaga) and shorthorn sculpin (Myoxocephalus scorpius). Navaga preyed mainly on benthic invertebrates, while sculpin preyed mainly on other fish species. A single individual of Atlantic cod (Gadus morhua) was also observed. Shorthorn sculpin and Atlantic cod have not previously been reported so far north in the Kara Sea. All taxa of macroalgae and benthic invertebrates observed in Stepovogo Fjord are common to the western coast of Novaya Zemlya and/or other areas in the Arctic. Currently there is no fishing activity in the immediate area in or around Stepovogo Fjord and only little commercial fishing in the Kara Sea due to the low commercial value of the species found in the area. Navaga and shorthorn sculpin do not make extensive migrations. As a result, the potential for the transfer of radioactive contamination to humans from consumption of fish and other seafood from this area is low at present.

Food-web structure varies along environmental gradients in a high-latitude marine ecosystem

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