Anna Gårdmark

Archival samples provide a unique source of DNA, offering the potential to extend the temporal scale of genetic studies by decades to centuries. Fish hard structures, such as otoliths and scales, serve as records for fish collected during fisheries monitoring across a large spatiotemporal scale. Operculum bones are a type of fish hard structure that, although less commonly collected, have been utilized in genetic studies. However, the usefulness of archived operculum bones to provide high quality whole genome sequence information has not been thoroughly evaluated. Here, we applied a commercially available extraction protocol, with minor adjustments, to isolate genomic DNA from operculum bones of Eurasian perch collected up to 47 years ago, followed by standard short-read whole genome sequencing. By comparing the metrics of DNA and whole genome sequencing data of bones with contemporary muscle samples, we demonstrate that the application of a simple extraction protocol on boiled archival fish operculum bones yields high quality genomic information that is comparable to fresh tissue, highlighting the role of archival operculum bones as an overlooked repository of valuable genomic information.

Climate warming reshapes biomass distributions across trophic levels in aquatic systems, with implications for ecosystem functioning and service provisioning. Using a space‐for‐time approach across temperate and boreal lakes, we analyse a dataset spanning wide gradients in temperature and nutrient availability, including species and biomass data for phytoplankton, fish, and, in some cases, zooplankton. We hypothesise that (1) warmer lakes have higher fish‐to‐phytoplankton biomass ratios than colder lakes, and (2) this relationship weakens at high phosphorus levels due to proliferation of inedible phytoplankton. Contrary to expectations, our results show that warmer lakes exhibit lower fish‐to‐phytoplankton biomass ratios, regardless of phosphorus concentrations or the contribution of benthic relative to whole lake primary production. This suggests reduced energy transfer efficiency from producers to consumers in warming waters. Changes in phytoplankton and fish community composition are likely part of the explanation for why increased phytoplankton biomass in warmer lakes does not translate into higher fish biomass. Our findings highlight a critical shift in biomass distribution from fish to phytoplankton with rising temperatures in northern lakes, potentially signalling future declines in food web efficiency and predator biomass under continued climate warming.

Body size is a key functional trait that has declined in many biological communities, partly due to changes in individual growth rates in response to climate warming. However, our understanding of growth responses in natural populations is limited by relatively short time series without large temperature contrasts and unknown levels of adaptation to local temperatures across populations within species. In this study, we collated back‐calculated length‐at‐age data for the fish Eurasian perch Perca fluviatilis from 10 populations along the Baltic Sea coast between 1953 and 2015 (142 023 length‐at‐age measurements). We fitted individual growth trajectories using the von Bertalanffy growth equation, and reconstructed local temperature time series using generalized linear mixed models fitted to three data sources. Leveraging a uniquely large temperature contrast due to climate change and artificial heating from nuclear power plants in two of the examined populations, we then estimated population‐specific and global (across populations) growth–temperature relationships using Bayesian mixed models, and evaluated whether populations are locally adapted to environmental temperatures. We found little evidence for local adaptation of body growth. Populations did not exhibit unique optimum growth temperatures nor unique growth rates at a common reference temperature. Instead, population‐specific curves mapped onto a global curve, resulting in body growth increasing with warming in cold populations but decreasing in one of the warmer populations. Understanding whether the effects of warming on growth are population‐specific is critical for generalizing predictions of climate impacts on body size, which affects multiple levels of biological organization from individuals to ecosystem functioning.

Klimatförändringen ger inte bara ökad medeltemperatur utan leder även till att olika typer av extremväder blir allt vanligare och intensivare. Extrema väderhändelser kan påverka livet i havet och därmed i förlängningen även de som är beroende och lever av vad havet kan ge i form av försörjning och rekreation. Extrema väderhändelser kan också ha en direkt påverkan på verksamheter till havs. Detta till trots, vet vi idag endast lite om hur extremväder till havs påverkar de marina ekosystemen och fisket. I den här rapporten summerar vi dialoger med representanter från olika svenska fiskesektorer om extremväders inverkan på deras verksamhet. Dialogerna har skett både i grupp (flera aktörer samtidigt) och med enskilda aktörer utifrån metoden ”semi-strukturerade intervjuer med öppna frågor”, där vi fokuserat på en handfull frågor om extremväders inverkan. Dialogerna påvisade uppenbara skillnader mellan sektorer i vad man upplever som extremväder, hur känslig sektorernas verksamhet är och hur den påverkas. Alla sektorer såg hårda vindar och stormar som extremväder som påverkar verksamheten, medan värmeböljor under sommaren endast nämndes av de aktörer som fiskar på kusten. Den upplevda känsligheten för påverkan från extremväder verkar vara som störst för småskaliga kustfiskare, sportfiskare och husbehovsfiskare som är knutna till en viss plats för sitt fiske, medan den upplevs som mindre för de aktörer som är mer flexibla och mobila i sin verksamhet. Avgörande för hur stor känsligheten för extremväder upplevs vara, är hur tillståndet för fiskbestånden och ekosystemen som nyttjas är, samt hur väl förvaltningen fungerar. Bland de värden som aktörerna lyfte som viktiga och som kunde påverkas av extremväder var monetära värden, men också livsstilsrelaterade värden som till exempel upplevelsen och kulturen som fisket associeras med. Sammantaget visade dialogerna att den viktigaste påverkan på fisket från extremväder upplevs ske indirekt genom att havsmiljön och fiskbestånden påverkas. Givet att förekomsten av extremväder blir mer vanligt, kan man därför inte utesluta en mer betydande påverkan på fisket i framtiden. Den traditionella fiskeförvaltningen som styr idag tar inte tillräcklig stor hänsyn till klimatets framtida inverkan på fiskbeståndens produktivitet och miljöns tillstånd, särskilt avseende de risker som orsakas av extrema väderhändelser. Välmående ekosystem och fiskbestånd i kombination med en förvaltning som kan anpassas till extrema väderhändelser bedöms därför vara avgörande för hur känsliga de olika sektorerna av det svenska fisket är och kommer att vara för påverkan från extremväder.

Predator responses to warming can occur via phenotypic plasticity, evolutionary adaptation or a combination of both, changing their top-down effects on prey communities. However, we lack evidence of how warming-induced evolutionary changes in predators may influence natural food webs. Here, we ask whether wild fish subject to warming across multiple generations differ in their impacts on prey communities compared with their nearby conspecifics experiencing a natural thermal regime. We carried out a common garden mesocosm experiment with larval perch ( Perca fluviatilis ), originating from a heated or reference coastal environment, feeding on zooplankton communities under a gradient of experimental temperatures. Overall, in the presence of fish of heated origin, zooplankton abundance was higher and did not change with experimental warming, whereas in the presence of fish of unheated origin, it declined with experimental temperature. Responses in zooplankton taxonomic and size composition suggest that larvae of heated origin consume more large-sized taxa as the temperature increases. Our findings show that differences between fish populations, potentially representing adaptation to their long-term thermal environments, can affect the abundance, biomass, size and species composition of their prey communities. This suggests that rapid microevolution in predators to ongoing climate warming might have indirect cross-generational ecological consequences propagating through food webs.

Predator responses to warming can occur via phenotypic plasticity and evolutionary adaptation, resulting in changes in their prey communities. However, we lack evidence of how warming-induced evolutionary changes in predators can influence the food web. Here, we ask whether fish subject to long-term warming across multiple generations differ in their impacts on prey communities compared to their nearby conspecifics experiencing a natural thermal regime. We carried out a common garden mesocosm experiment with larval perch ( Perca fluviatilis ), originating from one heated or one reference coastal environment, feeding on zooplankton communities under a gradient of experimental temperatures. We found that fish thermal origin influenced the zooplankton communities, and differently so depending on the experimental temperature. In presence of fish of heated origin, there were less zooplankton and also fewer individuals of large size, except for at intermediate experimental temperatures. Our findings show that differences between fish populations, potentially representing adaptation to local thermal environment, caused by multi-generational warming can cascade down via trophic interactions to also affect their zooplankton prey communities. Considering climate warming, our results suggest that rapid evolution in predators might have indirect cross-generational ecological consequences propagating through food webs.

Body size is a key functional trait that has declined in many biological communities, partly due to changes in individual growth rates in response to climate warming. However, our understanding of growth responses in natural ecosystems is limited by relatively short time series without large temperature contrasts and unknown levels of adaptation to local temperatures across populations. In this study, we collated back-calculated length-at-age data for the fish Eurasian perch ( Perca fluviatilis ) from 10 populations along the Baltic Sea coast between 1953–2015 (142023 length-at-age measurements). We fitted individual-level growth trajectories using the von Bertalanffy growth equation, and reconstructed local temperature time series using generalized additive models fitted to three data sources. Leveraging a uniquely large temperature contrast due to climate change and artificial heating, we then estimated population-specific and global growth-temperature relationships using Bayesian mixed models, and evaluated if they conformed to local adaption or not. We found little evidence for local adaptation in the temperature-dependence of individual growth curves. Instead, population-specific curves mapped onto a global curve, resulting in body growth increasing with warming in cold populations but decreasing in warm populations. Understanding to which degree the effects of warming on growth and size are population-specific is critical for generalizing predictions of climate impacts on growth, which is a key biological trait affecting multiple levels of biological organisation from individuals to ecosystem functioning.

Size-specific body growth responses to warming are common among animal taxa, but sex-specific responses are poorly known. Here we ask if body growth responses to warming are sex-dependent, and if such sex-specific responses vary with size and age. This was tested with sex-specific data of back-calculated individual growth trajectories, in European perch ( Perca fluviatilis) from a long-term whole-ecosystem warming experiment (6.3 °C above the surrounding sea). Warming led to both size- and sex-specific differences in growth responses. Warming had a consistent positive effect on body growth of females, but negative effects on male growth at size > 10 cm and age > 2 years. These sex-specific growth responses translate to an increased degree of female-biased sexual size dimorphism (in length-at-age) with warming. Although the exact temperature-mediated effects underlying differential growth responses could not be resolved, results imply global warming may have highly different effects during ontogeny of male and female perch. Such effects should be considered in climate warming scenarios concerning fish growth, population size-structure, and dynamics of aquatic food webs that include fish exhibiting sexual size dimorphism.

Ectotherms are predicted to ‘shrink’ with global warming, in line with general growth models and the temperature-size rule (TSR), both predicting smaller adult sizes with warming. However, they also predict faster juvenile growth rates and thus larger size-at-age of young organisms. Hence, the result of warming on the size-structure of a population depends on the interplay between how mortality rate, juvenile- and adult growth rates are affected by warming. Here, we use two-decade long time series of biological samples from a unique enclosed bay heated by cooling water from a nearby nuclear power plant to become 5–10 °C warmer than its reference area. We used growth-increment biochronologies (12,658 reconstructed length-at-age estimates from 2426 individuals) to quantify how >20 years of warming has affected body growth, size-at-age, and catch to quantify mortality rates and population size- and age structure of Eurasian perch (Perca fluviatilis). In the heated area, growth rates were faster for all sizes, and hence size-at-age was larger for all ages, compared to the reference area. While mortality rates were also higher (lowering mean age by 0.4 years), the faster growth rates lead to a 2 cm larger mean size in the heated area. Differences in the size-spectrum exponent (describing how the abundance declines with size) were less clear statistically. Our analyses reveal that mortality, in addition to plastic growth and size-responses, is a key factor determining the size structure of populations exposed to warming. Understanding the mechanisms by which warming affects the size- and the age structure of populations is critical for predicting the impacts of climate change on ecological functions, interactions, and dynamics.