Predicting differential effects of climate change at the population level with life-cycle models of spring Chinook salmon

Habitat conditions mediate the effects of climate, so neighboring populations with differing habitat conditions may differ in their responses to climate change. We have previously observed that juvenile survival in Snake River spring/summer Chinook salmon is strongly correlated with summer temperature in some populations and with fall streamflow in others. Here, we explore potential differential responses of the viability of four of these populations to changes in streamflow and temperature that might result from climate change. First, we linked predicted changes in air temperature and precipitation from several General Circulation Models to a local hydrological model to project streamflow and air temperature under two climate‐change scenarios. Then, we developed a stochastic, density‐dependent life‐cycle model with independent environmental effects in juvenile and ocean stages, and parameterized the model for each population. We found that mean abundance decreased 20–50% and the probability of quasi‐extinction increased dramatically (from 0.1–0.4 to 0.3–0.9) for all populations in both scenarios. Differences between populations were greater in the more moderate climate scenario than in the more extreme, hot/dry scenario. Model results were relatively robust to realistic uncertainty in freshwater survival parameters in all scenarios. Our results demonstrate that detailed population models can usefully incorporate climate‐change predictions, and that global warming poses a direct threat to freshwater stages in these fish, increasing their risk of extinction. Because differences in habitat may contribute to the individualistic population responses we observed, we infer that maintaining habitat diversity will help buffer some species from the impacts of climate change.     

Scenarios of freshwater fish extinctions from climate change and water withdrawal

Reductions in river discharge (water availability) like those from climate change or increased water withdrawal, reduce freshwater biodiversity. We combined two scenarios from the Intergovernmental Panel for Climate Change with a global hydrological model to build global scenarios of future losses in river discharge from climate change and increased water withdrawal. Applying these results to known relationships between fish species and discharge, we build scenarios of losses (at equilibrium) of riverine fish richness. In rivers with reduced discharge, up to 75% (quartile range 4–22%) of local fish biodiversity would be headed toward extinction by 2070 because of combined changes in climate and water consumption. Fish loss in the scenarios fell disproportionately on poor countries. Reductions in water consumption could prevent many of the extinctions in these scenarios.     

Climate change and freshwater biodiversity: detected patterns, future trends and adaptations in northern regions

Current rates of climate change are unprecedented, and biological responses to these changes have also been rapid at the levels of ecosystems, communities, and species. Most research on climate change effects on biodiversity has concentrated on the terrestrial realm, and considerable changes in terrestrial biodiversity and species’ distributions have already been detected in response to climate change. The studies that have considered organisms in the freshwater realm have also shown that freshwater biodiversity is highly vulnerable to climate change, with extinction rates and extirpations of freshwater species matching or exceeding those suggested for better‐known terrestrial taxa. There is some evidence that freshwater species have exhibited range shifts in response to climate change in the last millennia, centuries, and decades. However, the effects are typically species‐specific, with cold‐water organisms being generally negatively affected and warm‐water organisms positively affected. However, detected range shifts are based on findings from a relatively low number of taxonomic groups, samples from few freshwater ecosystems, and few regions. The lack of a wider knowledge hinders predictions of the responses of much of freshwater biodiversity to climate change and other major anthropogenic stressors. Due to the lack of detailed distributional information for most freshwater taxonomic groups and the absence of distribution‐climate models, future studies should aim at furthering our knowledge about these aspects of the ecology of freshwater organisms. Such information is not only important with regard to the basic ecological issue of predicting the responses of freshwater species to climate variables, but also when assessing the applied issue of the capacity of protected areas to accommodate future changes in the distributions of freshwater species. This is a huge challenge, because most current protected areas have not been delineated based on the requirements of freshwater organisms. Thus, the requirements of freshwater organisms should be taken into account in the future delineation of protected areas and in the estimation of the degree to which protected areas accommodate freshwater biodiversity in the changing climate and associated environmental changes.     

Climate‐induced warming imposes a threat to north European spring ecosystems

Interest in climate change effects on groundwater has increased dramatically during the last decade. The mechanisms of climate‐related groundwater depletion have been thoroughly reviewed, but the influence of global warming on groundwater‐dependent ecosystems (GDEs) remains poorly known. Here we report long‐term water temperature trends in 66 northern European cold‐water springs. A vast majority of the springs (82%) exhibited a significant increase in water temperature during 1968–2012. Mean spring water temperatures were closely related to regional air temperature and global radiative forcing of the corresponding year. Based on three alternative climate scenarios representing low (RCP2.6), intermediate (RCP6) and high‐emission scenarios (RCP8.5), we estimate that increase in mean spring water temperature in the region is likely to range from 0.67 °C (RCP2.6) to 5.94 °C (RCP8.5) by 2086. According to the worst‐case scenario, water temperature of these originally cold‐water ecosystems (regional mean in the late 1970s: 4.7 °C) may exceed 12 °C by the end of this century. We used bryophyte and macroinvertebrate species data from Finnish springs and spring‐fed streams to assess ecological impacts of the predicted warming. An increase in spring water temperature by several degrees will likely have substantial biodiversity impacts, causing regional extinction of native, cold‐stenothermal spring specialists, whereas species diversity of headwater generalists is likely to increase. Even a slight (by 1 °C) increase in water temperature may eliminate endemic spring species, thus altering bryophyte and macroinvertebrate assemblages of spring‐fed streams. Climate change‐induced warming of northern regions may thus alter species composition of the spring biota and cause regional homogenization of biodiversity in headwater ecosystems.     

Forecasting the effects of global change scenarios on bioaccumulation patterns in great lakes species

Climate change will have substantial impacts on biodiversity, particularly for aquatic species. Warming temperatures and changing weather patterns will also remobilize and modify chemical partitioning. Holding millions of cubic yards of sediments contaminated with persistent legacy chemicals such as polychlorinated biphenyls (PCBs) and dioxins, the Laurentian Great Lakes are a laboratory for observing interactions between biological and chemical responses to climate change. They provide a wide range of habitat to a variety of species, from littoral forage fish to deep‐water predators. In this paper, we couple bioenergetic and bioaccumulation models to investigate the biological and chemical effects of climate change in the Great Lakes. We consider three species: round goby, a warm‐water invasive forage fish; mottled sculpin, a cool‐water native forage fish; and lake trout, a cold‐water native predator. Using our coupled models, we calculate the accumulation of a representative persistent chemical, PCB‐77, under four climate scenarios for Lake Erie and Lake Superior. Predator–prey (lake trout–round goby) interactions and food availability (high–low) are incorporated into our simulations. For cool‐ to cold‐water species (sculpin, lake trout) we find that warm temperatures limit growth. For warm‐water species (round goby) cold temperatures limit growth. The impact of climate warming on growth depends on the winter lows as well as the summer highs of the scenario, in combination with the species' critical upper and lower thermal limits. We find conditions for high growth and consumption rates generally lead to high bioaccumulation. However, this can be confounded by predator–prey dynamics, as mismatches in the temperature preferences of predator and prey can lead to mismatches in relative growth and uptake rates. As predator–prey dynamics are expected to undergo substantial shifts with changing climate, these relative thermal sensitivities will be key in determining the implications of climate change for bioaccumulation, particularly in top predator species.     

Synthesizing the role of epigenetics in the response and adaptation of species to climate change in freshwater ecosystems

Freshwater ecosystems are amongst the most threatened ecosystems on Earth. Currently, climate change is one of the most important drivers of freshwater transformation and its effects include changes in the composition, biodiversity and functioning of freshwater ecosystems. Understanding the capacity of freshwater species to tolerate the environmental fluctuations induced by climate change is critical to the development of effective conservation strategies. In the last few years, epigenetic mechanisms were increasingly put forward in this context because of their pivotal role in gene–environment interactions. In addition, the evolutionary role of epigenetically inherited phenotypes is a relatively recent but promising field. Here, we examine and synthesize the impacts of climate change on freshwater ecosystems, exploring the potential role of epigenetic mechanisms in both short‐ and long‐term adaptation of species. Following this wrapping‐up of current evidence, we particularly focused on bringing together the most promising future research avenues towards a better understanding of the effects of climate change on freshwater biodiversity, specifically highlighting potential molecular targets and the most suitable freshwater species for future epigenetic studies in this context.     

Sea temperature is the primary driver of recent and predicted fish community structure across Northeast Atlantic shelf seas

Climate change has strongly influenced the distribution and abundance of marine fish species, leading to concern about effects of future climate on commercially harvested stocks. Understanding the key drivers of large-scale spatial variation across present-day marine assemblages enables predictions of future change. Here we present a unique analysis of standardised abundance data for 198 marine fish species from across the Northeast Atlantic collected by 23 surveys and 31,502 sampling events between 2005 and 2018. Our analyses of the spatially comprehensive standardised data identified temperature as the key driver of fish community structure across the region, followed by salinity and depth. We employed these key environmental variables to model how climate change will affect both the distributions of individual species and local community structure for the years 2050 and 2100 under multiple emissions scenarios. Our results consistently indicate that projected climate change will lead to shifts in species communities across the entire region. Overall, the greatest community-level changes are predicted at locations with greater warming, with the most pronounced effects at higher latitudes. Based on these results, we suggest that future climate-driven warming will lead to widespread changes in opportunities for commercial fisheries across the region.     

Contrasted impacts of climate change on stream fish assemblages along an environmental gradient

Aim To investigate the potential impacts of climate change on stream fish assemblages in terms of species and biological trait diversity, composition and similarity. Location One‐thousand one‐hundred and ten stream sections in France. Methods We predicted the future potential distribution of 35 common stream fish species facing changes in temperature and precipitation regime. Seven different species distribution models were applied and a consensus forecast was produced to limit uncertainty between single‐models. The potential impacts of climate change on fish assemblages were assessed using both species and biological trait approaches. We then addressed the spatial distribution of potential impacts along the upstream–downstream gradient. Results Overall, climate change was predicted to result in an increase in species and trait diversity. Species and trait composition of the fish assemblages were also projected to be highly modified. Changes in assemblages’ diversity and composition differed strongly along the upstream–downstream gradient, with upstream and midstream assemblages more modified than downstream assemblages. We also predicted a global increase in species and trait similarity between pairwise assemblages indicating a future species and trait homogenization of fish assemblages. Nevertheless, we found that upstream assemblages would differentiate, whereas midstream and downstream assemblages would homogenize. Our results suggested that colonization could be the main driver of the predicted homogenization, while local extinctions could result in assemblage differentiation. Main conclusions This study demonstrated that climate change could lead to contrasted impacts on fish assemblage structure and diversity depending on the position along the upstream–downstream gradient. These results could have important implications in terms of ecosystem monitoring as they could be useful in establishing areas that would need conservation prioritization.     

Determinants of fine‐scale homogenization and differentiation of native freshwater fish faunas in a Mediterranean Basin: implications for conservation

Aim Increasing threats to freshwater biodiversity are rapidly changing the distinctiveness of regional species pools and local assemblages. Biotic homogenization/differentiation processes are threatening the integrity and persistence of native biodiversity patterns at a range of spatial scales and pose a challenge for effective conservation planning. Here, we evaluate the extent and determinants of fine‐scale alteration in native freshwater fish assemblages among stream reaches throughout a large river basin and consider the implications of these changes for the long‐term conservation of native fishes. Location Guadiana River basin (South‐Western Iberian Peninsula). Methods We quantified the magnitude of change in compositional similarity between observed and reference assemblages and its potential effect on natural patterns of compositional distinctiveness. Reference assemblages were defined as the native species expected to occur naturally (in absence of anthropogenic alterations) and were reconstructed using a multivariate adaptive regression splines predictive model. We also evaluated the role of habitat degradation and introduced species as determinants of biotic homogenization/differentiation. Results We found a significant trend towards homogenization for native fish assemblages. Changes in native fish distributions led to the loss of distinctiveness patterns along natural environmental gradients. Introduced species were the most important factor explaining the homogenization process. Homogenization of native assemblages was stronger in areas close to reservoirs and in lowland reaches where introduced species were more abundant. Main conclusions The implementation of efficient conservation for the maintenance of native fish diversity is seriously threatened by the homogenization processes. The identification of priority areas for conservation is hindered by the fact that the most diverse communities are vanishing, which would require the selection of broader areas to adequately protect all the species. Given the principal role that introduced species play in the homogenization process and their relation with reservoirs, special attention must be paid to mitigating or preventing these threats.     

Eight decades of sampling reveal a contemporary novel fish assemblage in coastal nursery habitats

In order to adequately monitor biodiversity trends through time and their responses to natural or anthropogenic impacts, researchers require long time series that are often unavailable. This general lack of datasets that are several decades or longer makes establishing a background or baseline of diversity metrics difficult – especially when attempting to understand species composition changes against a backdrop of climate and ecological variability. Here, we present an analysis of a community of juvenile nearshore fishes based on nearly 8 decades of highly standardized Norwegian survey records. Using multivariate statistical techniques, we: (i) characterize the change in taxonomic community composition through time, (ii) determine whether there has been an increase in warm‐water affinity species relative to their cold water affinity counterparts, and (iii) characterize the temporal change in the species’ functional trait assemblage. Our results strongly indicate a shift toward a novel fish assemblage between the late 1990s and 2000s. The context of changes within the most recent two decades is in stark contrast to those during the 1960s and 1970s, but similar to those during the previous warm period during the 1930s and 1940s. This novel assemblage is tightly linked to the warming temperatures in the region portrayed by the increased presence of warm‐water species and a higher incidence of pelagic, planktivorous species. The results indicate a clear influence of ocean temperature on the region's juvenile fish community that points to climate‐mediated effects on the species assemblages of an important fish nursery area.     

BIODIVERSITY RESEARCH: Geographical linkages between threats and imperilment in freshwater fish in the Mediterranean Basin

Aim The level of imperilment of mediterranean freshwater fish is among the highest recorded for any group of organisms evaluated to date. Here, we describe the geographical patterns in the incidence of threats affecting mediterranean freshwater fish and test whether the effects of specific threats are spatially related to the degree of imperilment of fish faunas. Location The Mediterranean Basin Biome. Methods From the IUCN Red List, we recorded the six main threats to 232 endemic freshwater fish species. We used data on fish distributions from IUCN to characterize the spatial patterns in the incidence of threats (as percentage of species affected) through multivariate statistics. We studied the relationships between threat incidence and two estimators of imperilment (proportion of species threatened and an index of extinction risk) at two spatial scales (10 × 10 km and basins) using partial least squares regressions (PLSR) that incorporated the effects of species richness and mean range size. Results The main axis of variation in the incidence of threats to freshwater fish split areas mainly affected by invasive species from those areas where species are threatened by pollution and agriculture. Wherever invasive species and water extraction were predominant threats, fish assemblages consistently tended to be more imperilled. Main conclusions As far as we know, this is the first large‐scale analysis on the spatial relationships between the incidence of threats and level of imperilment of any taxonomic group. Our results highlight the primary role of invasive species and water extraction as drivers of native fish declines in the Mediterranean Basin. Large‐scale patterns described here should be generated by local‐scale impacts of both threats on fish biodiversity, widely reported in Mediterranean areas. Because all the species under concern are endemic, control of invasive species and reducing overexploitation of freshwater resources should be conservation priorities for mediterranean freshwater systems.     

Climate change,woodpeckers, and forests: Current trends and future modeling needs

The structure and composition of forest ecosystems are expected to shift with climate‐induced changes in precipitation, temperature, fire, carbon mitigation strategies, and biological disturbance. These factors are likely to have biodiversity implications. However, climate‐driven forest ecosystem models used to predict changes to forest structure and composition are not coupled to models used to predict changes to biodiversity. We proposed integrating woodpecker response (biodiversity indicator) with forest ecosystem models. Woodpeckers are a good indicator species of forest ecosystem dynamics, because they are ecologically constrained by landscape‐scale forest components, such as composition, structure, disturbance regimes, and management activities. In addition, they are correlated with forest avifauna community diversity. In this study, we explore integrating woodpecker and forest ecosystem climate models. We review climate–woodpecker models and compare the predicted responses to observed climate‐induced changes. We identify inconsistencies between observed and predicted responses, explore the modeling causes, and identify the models pertinent to integration that address the inconsistencies. We found that predictions in the short term are not in agreement with observed trends for 7 of 15 evaluated species. Because niche constraints associated with woodpeckers are a result of complex interactions between climate, vegetation, and disturbance, we hypothesize that the lack of adequate representation of these processes in the current broad‐scale climate–woodpecker models results in model–data mismatch. As a first step toward improvement, we suggest a conceptual model of climate–woodpecker–forest modeling for integration. The integration model provides climate‐driven forest ecosystem modeling with a measure of biodiversity while retaining the feedback between climate and vegetation in woodpecker climate change modeling.     

Interbasin water transfer, riverine connectivity, and spatial controls on fish biodiversity

Background

Large-scale inter-basin water transfer (IBWT) projects are commonly proposed as solutions to water distribution and supply problems. These problems are likely to intensify under future population growth and climate change scenarios. Scarce data on the distribution of freshwater fishes frequently limits the ability to assess the potential implications of an IBWT project on freshwater fish communities. Because connectivity in habitat networks is expected to be critical to species'' biogeography, consideration of changes in the relative isolation of riverine networks may provide a strategy for controlling impacts of IBWTs on freshwater fish communities.

Methods/Principal Findings

Using empirical data on the current patterns of freshwater fish biodiversity for rivers of peninsular India, we show here how the spatial changes alone under an archetypal IBWT project will (1) reduce freshwater fish biodiversity system-wide, (2) alter patterns of local species richness, (3) expand distributions of widespread species throughout peninsular rivers, and (4) decrease community richness by increasing inter-basin similarity (a mechanism for the observed decrease in biodiversity). Given the complexity of the IBWT, many paths to partial or full completion of the project are possible. We evaluate two strategies for step-wise implementation of the 11 canals, based on economic or ecological considerations. We find that for each step in the project, the impacts on freshwater fish communities are sensitive to which canal is added to the network.

Conclusions/Significance

Importantly, ecological impacts can be reduced by associating the sequence in which canals are added to characteristics of the links, except for the case when all 11 canals are implemented simultaneously (at which point the sequence of canal addition is inconsequential). By identifying the fundamental relationship between the geometry of riverine networks and freshwater fish biodiversity, our results will aid in assessing impacts of IBWT projects and balancing ecosystem and societal demands for freshwater, even in cases where biodiversity data are limited.     

Impacts of drought and predicted effects of climate change on fish growth in temperate Australian lakes

Climate change is expected to negatively impact many freshwater environments due to reductions in stream‐flow and increases in temperature. These conditions, however, can already be found today in areas experiencing significant drought; current observations of species' responses to droughts can be used to make predictions about their future responses to climate change. Using otolith analysis, we recreated golden perch (Macquaria ambigua) growth chronologies from two temperate lake populations in southeastern Australia over a 15‐year period pre‐ and during a supraseasonal drought. We related interannual growth variation to landscape‐scale changes in temperature and hydrological regimes: fish growth declined as water levels in the lakes dropped during the drought, but this effect was offset by increased growth in warmer years. We hypothesize that golden perch are responding to fluctuations in food availability and intraspecific competition related to water level and to an optimization of physiological growth conditions related to increases in growing season length. Based on our analyses, we made predictions of future growth under a number of climate change scenarios that incorporate forecast deviations in stream‐flows and air temperature. Despite climatic models predicting significant declines in future water availability, fish growth may increase due to a disproportionate lengthening of the growing season. As the two lakes are at the limit of the southerly range of golden perch, our results are consistent with previous findings of climate‐change driven latitudinal range shifts in a poleward direction. We discuss assumptions concerning the constancy of ecological interactions into the future that warrant further study. Our research provides a novel application of biochronological analysis that could be used elsewhere to further our knowledge of species responses to changing environments.     

Strong spatial turnover in cichlid fish assemblages in the upper río Madera (Amazon basin) despite the absence of hydrological barriers

In freshwater ecosystems, spatial turnover in fish assemblages is often attributed to dispersal limitation imposed by fragmentation of water bodies. Other factors like environmental properties or biotic interactions have often been assumed to be minute relative to dispersal limitation when hydrogeological barriers are abundant. This study aims to describe the spatial differentiation of cichlid fish assemblages in the upper río Madera in Bolivia, Brazil and Perú, a large drainage system characterized by the absence of significant hydrogeological barriers. We assessed the relative importance of spatial, climatic and geological predictors in the observed biogeographic structure using an integrative combination of cluster analyses, elements of metacommunity structure analysis, variation partitioning, and network analysis. Our results show that distinct assemblages of cichlid fish species replace each other across the landscape and that this turnover is partially determined by climate and geological gradients. A considerable fraction of the cichlid assembly structure could not be assigned to either space, climate or geology and might be explained by unmeasured parameters such as habitat structure or biotic interactions. Incorporating knowledge on spatial turnover of species assemblages into conservation strategies will be essential for the biodiversity management of the diverse aquatic fauna of the upper río Madera.     

Conceptualising the interactive effects of climate change and biological invasions on subarctic freshwater fish

Climate change and species invasions represent key threats to global biodiversity. Subarctic freshwaters are sentinels for understanding both stressors because the effects of climate change are disproportionately strong at high latitudes and invasion of temperate species is prevalent. Here, we summarize the environmental effects of climate change and illustrate the ecological responses of freshwater fishes to these effects, spanning individual, population, community and ecosystem levels. Climate change is modifying hydrological cycles across atmospheric, terrestrial and aquatic components of subarctic ecosystems, causing increases in ambient water temperature and nutrient availability. These changes affect the individual behavior, habitat use, growth and metabolism, alter population spawning and recruitment dynamics, leading to changes in species abundance and distribution, modify food web structure, trophic interactions and energy flow within communities and change the sources, quantity and quality of energy and nutrients in ecosystems. Increases in temperature and its variability in aquatic environments underpin many ecological responses; however, altered hydrological regimes, increasing nutrient inputs and shortened ice cover are also important drivers of climate change effects and likely contribute to context‐dependent responses. Species invasions are a complex aspect of the ecology of climate change because the phenomena of invasion are both an effect and a driver of the ecological consequences of climate change. Using subarctic freshwaters as an example, we illustrate how climate change can alter three distinct aspects of species invasions: (1) the vulnerability of ecosystems to be invaded, (2) the potential for species to spread and invade new habitats, and (3) the subsequent ecological effects of invaders. We identify three fundamental knowledge gaps focused on the need to determine (1) how environmental and landscape characteristics influence the ecological impact of climate change, (2) the separate and combined effects of climate and non‐native invading species and (3) the underlying ecological processes or mechanisms responsible for changes in patterns of biodiversity.     

The combined effects of climate change and river fragmentation on the distribution of Andean Amazon fishes

Upstream range shifts of freshwater fishes have been documented in recent years due to ongoing climate change. River fragmentation by dams, presenting physical barriers, can limit the climatically induced spatial redistribution of fishes. Andean freshwater ecosystems in the Neotropical region are expected to be highly affected by these future disturbances. However, proper evaluations are still missing. Combining species distribution models and functional traits of Andean Amazon fishes, coupled with dam locations and climatic projections (2070s), we (a) evaluated the potential impacts of future climate on species ranges, (b) investigated the combined impact of river fragmentation and climate change and (c) tested the relationships between these impacts and species functional traits. Results show that climate change will induce range contraction for most of the Andean Amazon fish species, particularly those inhabiting highlands. Dams are not predicted to greatly limit future range shifts for most species (i.e., the Barrier effect). However, some of these barriers should prevent upstream shifts for a considerable number of species, reducing future potential diversity in some basins. River fragmentation is predicted to act jointly with climate change in promoting a considerable decrease in the probability of species to persist in the long‐term because of splitting species ranges in smaller fragments (i.e., the Isolation effect). Benthic and fast‐flowing water adapted species with hydrodynamic bodies are significantly associated with severe range contractions from climate change.     

Coextirpation of host–affiliate relationships in rivers: the role of climate change,water withdrawal,and host‐specificity

The role of climate‐related disturbances on complex host–affiliate relationships remains understudied, largely because affiliate species vary in host use and are often differentially susceptible to disturbance relative to their hosts. Here we report the first set of host–affiliate species–discharge relationships (SDR) in freshwater and examine how anticipated shifts in water availability (flow) will impact coextirpations. We used SDR for freshwater mussels and fish across 11 regions (over 350 rivers) in the continental United States that we coupled to future water availability (2070) to model mussel and fish coextirpations. We also used river‐specific host–affiliate matrices (presence–absence) to evaluate how host‐specificity (mean number of hosts used by an affiliate) and host‐overlap (extent to which affiliates share hosts) relate to extirpation vulnerability. We found that the strength and predictability of SDR models vary geographically and that mussels were more susceptible to flow alterations than fish. These patterns of extirpations were strongest in the southeast where: (1) flow reductions are expected to be greatest; (2) more species are lost per unit flow; (3) and more mussels are expected to be lost per unit of fish. We also found that overall mussel losses associated with reduction in habitat (water availability) were greater than those associated with loss of fish hosts which we assumed to be a function of host redundancy. These findings highlight the utility of SDR as a tool for conservation efforts but they also demonstrate the potential severity of reductions in mussel and fish richness as consequence of climate change and water use. Mussels provide key ecosystem services but face multiple pronged attacks from reductions in flow, habitat, and fish hosts. These losses in biodiversity and ecosystem functions can translate into major effects on food webs and nutrient recycling.     

Warming shelf seas drive the subtropicalization of European pelagic fish communities

Pelagic fishes are among the most ecologically and economically important fish species in European seas. In principle, these pelagic fishes have potential to demonstrate rapid abundance and distribution shifts in response to climatic variability due to their high adult motility, planktonic larval stages, and low dependence on benthic habitat for food or shelter during their life histories. Here, we provide evidence of substantial climate‐driven changes to the structure of pelagic fish communities in European shelf seas. We investigated the patterns of species‐level change using catch records from 57 870 fisheries‐independent survey trawls from across European continental shelf region between 1965 and 2012. We analysed changes in the distribution and rate of occurrence of the six most common species, and observed a strong subtropicalization of the North Sea and Baltic Sea assemblages. These areas have shifted away from cold‐water assemblages typically characterized by Atlantic herring and European sprat from the 1960s to 1980s, to warmer‐water assemblages including Atlantic mackerel, Atlantic horse mackerel, European pilchard and European anchovy from the 1990s onwards. We next investigated if warming sea temperatures have forced these changes using temporally comprehensive data from the North Sea region. Our models indicated the primary driver of change in these species has been sea surface temperatures in all cases. Together, these analyses highlight how individual species responses have combined to result in a dramatic subtropicalization of the pelagic fish assemblage of the European continental shelf.