Michaela Aschan

Basin-Scale Coherence in Phenology of Shrimps and Phytoplankton in the North Atlantic Ocean

Fine-Tuning Fisheries The past decade has seen a tremendous increase in our understanding of how climate anomalies affect hydrographic properties in North Atlantic Shelf ecosystems, but less about how these events impact organisms. Koeller et al. (p. 791, see the Perspective by Greene et al.) measured the egg incubation and hatching times of an important fisheries resource, the pink North Atlantic shrimp, at a variety of locations and compared them to the timing of the local spring phytoplankton bloom. Shrimp reproduction was determined locally by bottom-water temperatures and was not directly coupled with the spring bloom. While the local bottom temperatures and bloom timing are well-matched in general, and match egg hatching to food availability, this evolved relationship can be decoupled by interannual variability and climate change. Shrimp reproduction is primed by bottom temperature and not directly by cues from the spring phytoplankton bloom. Climate change could lead to mismatches between the reproductive cycles of marine organisms and their planktonic food. We tested this hypothesis by comparing shrimp (Pandalus borealis) egg hatching times and satellite-derived phytoplankton bloom dynamics throughout the North Atlantic. At large spatial and long temporal (10 years or longer) scales, hatching was correlated with the timing of the spring phytoplankton bloom. Annual egg development and hatching times were determined locally by bottom water temperature. We conclude that different populations of P. borealis have adapted to local temperatures and bloom timing, matching egg hatching to food availability under average conditions. This strategy is vulnerable to interannual oceanographic variability and long-term climatic changes.

Latitudinal gradients in the structure of macrobenthic communities: a comparison of Arctic, temperate and tropical sites

Abstract As part of a programme to re-assess the existence of latitudinal gradients in the diversity of the macrobenthic infauna of soft sediments, samples were taken from Sassenfjord, Spitzbergen. Abundancebiomass curves showed the shallowest sites to be moderately disturbed, possibly as a result of glacial run-off from the Gipselva. These clearly differed from a site at 123 m which appeared to be in an undisturbed state. A comparison of the diversity profile of the latter site (78 °N) with those of physically similar sites in the North Sea (55 °N) and off the coast of Java (7 °S), sampled by identical methods, shows no real difference in diversity.

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.

Fish assemblages in the Barents Sea

Abstract Fish species inhabiting the Barents Sea display great seasonal and inter-annual variation in abundance and distribution. This study describes the assemblages and distributions of fish species in the southwestern and central part of the Barents Sea, which includes the polar front. The area has an unpredictable environment due to variable inflow of Atlantic water and fish species composition differs between Arctic and Atlantic water masses. Assemblages can be identified as distinct groups corresponding to different environmental conditions. In the period 1997–1999, 57 fish species and shrimp were identified and 29 species/species groups were used in the statistical analyses. Cluster and correspondence analyses showed that the fish community consists of four assemblages: a northern, a southern, a deep and a central group. Temperature explained 26.2% of the variation in the species data, and depth 14.5% of the variation. The assemblages are coherent with previous zoogeographical studies from the Barents Sea. To reduce research costs, one might monitor indicator species characteristic for the identified fish assemblages. Fish assemblages may be a good tool when studying ecosystem responses to fishery and marine climate change.

Population structure of the deep-sea shrimp (Pandalus borealis) in the north-east Atlantic based on allozyme variation.

In order to elucidate the population structure of the deep-sea shrimp ( Pandalus borealis) in the NE Atlantic, 32 subsamples and 3 865 individuals were analysed for allozymic variation. They were caught at various locations in the Barents Sea, in waters off Svalbard, Jan Mayen and Iceland, and in fjords along the Norwegian coast. Only three enzymes (malate dehydrogenase, phosphoglucomutase and glucosephosphate isomerase) of the 22 initially tested showed a combination of gel images that could be interpreted with confidence and allozymic variation. The locus coding for malate dehydrogenase was by far the most polymorphic. Samples caught within the Barents Sea and in the Svalbard area showed no significant heterogeneity in allele frequencies, supporting earlier suggestions of only one population of P. borealis in the Barents Sea. Genetic differentiation was found, however, between Norwegian fjords and the Barents Sea, and among fjords.

Who eats whom in the Barents Sea: a food web topology from plankton to whales

A food web is an ecological network and its topological description consists of the list of nodes, i.e., trophospecies, the list of links, i.e., trophic interactions, and the direction of interactions (who is the prey and who is the predator). Food web topologies are widely used in ecology to describe structural properties of communities or ecosystems. The selection of trophospecies and trophic interactions can be realized in different manners so that many different food webs may be constructed for the same community. In the Barents Sea, many simple food webs have been constructed. We present a comprehensive food web topology for the Barents Sea ecosystem, from plankton to marine mammals. The protocol used to compile the data set includes rules for the selection of taxa and for the selection and documentation of the trophic links. The resulting topology, which includes 244 taxa and 1589 trophic links, can serve as a basis for topological analyses, comparison with other marine ecosystems, or as a basis to ...

Effects of changes in sewage pollution on soft-botiom macrofauna communities in the inner Oslofjord, Norway

Abstract The macrobenthic fauna of Vestfjorden, inner Oslofjord was sampled in 1980 and 1985 at 19 stations. The aim of this study was to detect possible faunal changc:s following the start of a sewage treatment plant in 1982. The faunal data were analyzed by a variety of methods including diversity indices, log-normal distribution of individuals among species and classification and ordination analysis. The results show a decline in species number and abundance which may be related to increased pollution. However, the diversity and the evenness have increased. The area within a radius of 2-3 km from the outlet of the treatment plant shows clear pollution effects while the marginal areas show improved conditions.

Life history variation in Barents Sea fish: implications for sensitivity to fishing in a changing environment.

Under exploitation and environmental change, it is essential to assess the sensitivity and vulnerability of marine ecosystems to such stress. A species’ response to stress depends on its life history. Sensitivity to harvesting is related to the life history “fast–slow” continuum, where “slow” species (i.e., large, long lived, and late maturing) are expected to be more sensitive to fishing than “fast” ones. We analyze life history traits variation for all common fish species in the Barents Sea and rank fishes along fast–slow gradients obtained by ordination analyses. In addition, we integrate species’ fast–slow ranks with ecosystem survey data for the period 2004–2009, to assess life history variation at the community level in space and time. Arctic fishes were smaller, had shorter life spans, earlier maturation, larger offspring, and lower fecundity than boreal ones. Arctic fishes could thus be considered faster than the boreal species, even when body size was corrected for. Phylogenetically related species possessed similar life histories. Early in the study period, we found a strong spatial gradient, where members of fish assemblages in the southwestern Barents Sea displayed slower life histories than in the northeast. However, in later, warmer years, the gradient weakened caused by a northward movement of boreal species. As a consequence, the northeast experienced increasing proportions of slower fish species. This study is a step toward integrating life history traits in ecosystem-based areal management. On the basis of life history traits, we assess the fish sensitivity to fishing, at the species and community level. We show that climate warming promotes a borealization of fish assemblages in the northeast, associated with slower life histories in that area. The biology of Arctic species is still poorly known, and boreal species that now establish in the Arctic are fishery sensitive, which calls for cautious ecosystem management of these areas.

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.

Change in Fish Community Structure in the Barents Sea

Change in oceanographic conditions causes structural alterations in marine fish communities, but this effect may go undetected as most monitoring programs until recently mainly have focused on oceanography and commercial species rather than on whole ecosystems. In this paper, the objective is to describe the spatial and temporal changes in the Barents Sea fish community in the period 1992–2004 while taking into consideration the observed abundance and biodiversity patterns for all 82 observed fish species. We found that the spatial structure of the Barents Sea fish community was determined by abiotic factors such as temperature and depth. The observed species clustered into a deep assemblage, a warm water southern assemblage, both associated with Atlantic water, and a cold water north-eastern assemblage associated with mixed water. The latitude of the cold water NE and warm water S assemblages varied from year to year, but no obvious northward migration was observed over time. In the period 1996–1999 we observed a significant reduction in total fish biomass, abundance, mean fish weight, and a change in community structure including an increase in the pelagic/demersal ratio. This change in community structure is probably due to extremely cold conditions in 1996 impacting on a fish community exposed to historically high fishing rates. After 1999 the fish community variables such as biomass, abundance, mean weight, P/D ratio as well as community composition did not return to levels of the early 90s, although fishing pressure and climatic conditions returned to earlier levels.