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The impacts of climate change are widespread and threaten natural systems globally. Yet, within regions, heterogeneous physical landscapes can differentially filter climate, leading to local response diversity. For example, it is possible that while freshwater lakes are sensitive to climate change, they may exhibit a diversity of thermal responses owing to their unique morphology, which in turn can differentially affect the growth and survival of vulnerable biota such as fishes. In particular, salmonids are cold‐water fishes with complex life histories shaped by diverse freshwater habitats that are sensitive to warming temperatures. Here we examine the influence of habitat on the growth of sockeye salmon (Oncorhynchus nerka) in nursery lakes of Canada's Skeena River watershed over a century of change in regional temperature and intraspecific competition. We found that freshwater growth has generally increased over the last century. While growth tended to be higher in years with relatively higher summer air temperatures (a proxy for lake temperature), long‐term increases in growth appear largely influenced by reduced competition. However, habitat played an important role in modulating the effect of high temperature. Specifically, growth was positively associated with rising temperatures in relatively deep (>50 m) nursery lakes, whereas warmer temperatures were not associated with a change in growth for fish among shallow lakes. The influence of temperature on growth also was modulated by glacier extent whereby the growth of fish from lakes situated in watersheds with little (i.e., <5%) glacier cover increased with rising temperatures, but decreased with rising temperatures for fish in lakes within more glaciated watersheds. Maintaining the integrity of an array of freshwater habitats—and the processes that generate and maintain them—will help foster a diverse climate‐response portfolio for important fish species, which in turn can ensure that salmon watersheds are resilient to future environmental change. [ABSTRACT FROM AUTHOR]

• Parasite infections often peak in certain seasons in aquatic ecosystems. • Meta-analysis of 693 seasonal infection contrasts reveals no universal pattern. • Taxon-specific patterns rule among winter-summer and wet-dry season infection dynamics. • The same parasite taxa show contrasting patterns between freshwater and marine habitats. • Sensitivity to abiotic conditions therefore varies widely among host-parasite systems. Seasonal infection dynamics characterise many host-parasite interactions, as abiotic conditions drive fundamental biological processes in both hosts and parasites. The extent to which seasonal cycles in parasite abundance are universal, and whether the same underlying mechanisms are responsible for seasonality across different host-parasite associations, have received little attention to date. Here, global patterns of seasonal infection dynamics are tested using a meta-analysis of 693 seasonal contrasts in the local abundance of metazoan parasites in aquatic vertebrates, representing 343 parasite species and 148 host species. These include both contrasts between winter and summer in temperate systems, and between wet and dry seasons in tropical systems. Overall, the analysis found no evidence that seasonal infection dynamics are universal, nor that they are controlled by the same factors. More specifically, the results indicate no overall effect of the magnitude of local seasonal differences in abiotic conditions (temperature or precipitation), type of host (amphibian or fish), habitat (freshwater, coastal marine or deep-sea), host body length, or mode of transmission (skin contact or trophic) on the extent of seasonal differences in parasite infections. Instead, the results revealed many clear taxon-specific or habitat-specific patterns of seasonal infection dynamics, with some parasite or host taxa generally showing distinct peaks in infections in summer or dry seasons, and others showing no seasonal changes. The present findings serve to identify empirically which host-parasite associations are most likely to respond to changing climatic conditions, and thus provide useful information for fisheries and aquaculture. [ABSTRACT FROM AUTHOR]

Formation of diatom frustules depends on the process of silicification. In many planktonic species of algae, ambient temperature and nutrients are already known to affect growth and morphology, making them suitable bioindicators. In this study, a similar indicator function of benthic diatoms is proposed based on the principle that cell wall thickness is inversely proportional to temperature and nutrients. Therefore, higher turnover rates at warmer temperatures are hypothesized to favour smaller and lighter diatoms due to their shorter regeneration time. Accordingly, benthic diatom species were classified into seven categories according to their intensity of silicification, referred to as 'Silicification Value'. For each diatom assemblage, an abundance-weighted average silicification value was calculated and tested for its applicability to assess global change impact on mountain lakes in the northern calcareous Alps of Europe. Surface sediment diatom samples and morphometric and ecological parameters of 41 lakes from a wide altitudinal range in the Bavarian and Tyrolian Alps were collected and analysed. Statistical tests revealed that temperature conditions in a lake and its altitude were the most decisive proxies related to the 'Silicification Value'. Moreover, trophic status and the presence of macrophytes had some influence. This supported the hypothesis that lakes, which are warmer and richer in nutrients, show a weaker average silicification in diatom assemblages. A dependence of silicification on valve size could be shown but appears to be negligible in climatological issues. In particular, the correlation with temperature makes the silicification value an applicable palaeoecological proxy to assess climate change impact in freshwater lakes. [ABSTRACT FROM AUTHOR]

Climate change is a growing global issue with many countries and institutions declaring a climate state of emergency. Excess CO 2 from anthropogenic sources and changes in land use practices are contributing to many detrimental changes, including increased global temperatures, ocean acidification and hypoxic zones along coastal habitats. All senses are important for aquatic animals, as it is how they can perceive and respond to their environment. Some of these environmental challenges have been shown to impair their sensory systems, including the olfactory, visual, and auditory systems. While most of the research is focused on how ocean acidification affects olfaction, there is also evidence that it negatively affects vision and hearing. The effects that temperature and hypoxia have on the senses have also been investigated, but to a much lesser extent in comparison to ocean acidification. This review assembles the known information on how these anthropogenic challenges affect the sensory systems of fishes, but also highlights what gaps in knowledge remain with suggestions for immediate action. Olfaction, vision, otolith, pH, freshwater, seawater, marine, central nervous system, electrophysiology, mechanism. [Display omitted] • Conditions in abiotic factors of oceans and freshwater habitats are changing quickly due to anthropogenic activity. • Low pH impairs olfaction and vision, alters otolith growth, and affects CNS functioning. • High temperatures increase the signalling speed of nerves, alters sensory processing, and increases ROS in the CNS. • Low oxygen impairs energy production, nerve conduction speed, negatively affects vision and causes apoptosis in the brain. [ABSTRACT FROM AUTHOR]

Abstract: There is growing evidence that climate change has greatly altered environmental conditions in many aquatic ecosystems over the last decades, leading to changes in fish distribution and life history traits. Recent works conducted in Senegalese and Gambian coastal marine, estuarine and freshwater ecosystems have shown important changes in the intensity, frequency and breeding timing of wild population of Sarotherodon melanotheron in response to changes in salinity regimes. In addition to salinity, this study investigates the potential influences of other environmental factors that have received less attention on the reproduction of S. melanotheron from three different aquatic ecosystems in Senegal. The results demonstrate that day-length and temperature affect sexual maturity in both males and females from Guiers Lake and Hann Bay, but no such effects were found in upstream of the Saloum Estuary, where the spawning activity seems to be under the synergetic control of rainfall and salinity that apparently predominate over all the other ambient factors. This study demonstrated for the first time that aside from photoperiod and temperature, rainfall also influences fish reproduction in Hann Bay probably through its effects on water quality. Furthermore, our results confirm previous findings that changes in salinity regimes resulting from seasonal variations in precipitation and evaporation are the ultimate causes of temporal changes in the reproductive activity of the species in this estuary. [Copyright &y& Elsevier]

• Cell concentration increased more with temperature than pCO2 in continuous cultures. • Species and strains differed in growth response to increased temperature and pCO2. • Straight R. raciborskii strains have five more carbon acquisition genes than coiled. • Straight strain cell concentration increased more with higher pCO2 than coiled strain. Global increases in atmospheric CO 2 and temperatures will impact aquatic systems, with freshwater habitats being affected. Some studies suggest that these conditions will promote cyanobacterial dominance. There is a need for a clearer picture of how algal species and strains within species will respond to higher temperatures and CO 2 , especially in combination. This study examined two chlorophytes (Monoraphidium and Staurastrum), and two strains of the cyanobacterium Raphidiopsis raciborskii (straight S07 and coiled C03), to determine how the combination of higher temperature and CO 2 levels will affect their growth and maximum cell concentrations. Continuous cultures were used to compare the steady state cell concentrations at 28 °C and 30 °C, and CO 2 partial pressures (pCO 2), 400 and 750 ppm for all cultures, and in addition 1000 ppm at 28 °C for R. raciborskii strains. This study showed that, for all species, water temperature had a greater effect than higher pCO 2 on cell concentrations. There were clear differences in response between the chlorophyte species, with Monoraphidium preferring 28 °C and Staurastrum preferring 30 °C. There were also differences in response of the R. raciborskii strains to increasing temperature and pCO 2 , with S07 having a greater increase in cell concentration. Genome analysis of R. raciborskii showed that the straight strain has five additional carbon acquisition genes (β-CA , chpY , cmpB , cmpD and NdhD4), indicative of increased carbon metabolism. These differences in the strains' response to elevated pCO 2 will lead to changes in the species population structure and distribution in the water column. This study shows that it is important to examine the effects of both pCO 2 and temperature, and to consider strain variation, to understand how species composition of natural systems may change under future climate conditions. [ABSTRACT FROM AUTHOR]