To What Extent Can Existing Research Help Project Climate Change Impacts on Biodiversity in Aquatic Environments? A Review of Methodological Approaches

Transcriptional dynamic changes in energy metabolism, protein synthesis and cell cycle regulation reveal the biological adaptation mechanisms of juvenile Acrossocheilus wenchowensis under acute temperature changes

In recent years, frequent acute temperature changes have posed a serious threat to the physiology and survival of fish. This study utilized RNA-Seq technology to analyze the transcriptional dynamics in the muscle tissues of Acrossocheilus wenchowensis under various acute temperature conditions (16◦C, 20◦C, 24◦C, 28◦C and 32◦C). Through comprehensive analysis, we identified 11509 differentially expressed genes (DEGs), a gene set (profiles 19) that was significantly up-regulated with increasing temperature, and two weighted gene co-expression network analysis (WGCNA) modules that were significantly correlated with acute temperature changes. Furthermore, we identified 28 transcription factors that are pivotal in oxidative stress and energy metabolism under acute temperature changes. Our results showed that, compared to the control group (24°C), KEGG functional enrichment analysis revealed significant enrichment of DEGs in the cell cycle, DNA replication, and p53 signaling pathway, with an overall trend of suppressed expression. This indicates that maintaining cell stability and reducing cell damage is an effective adaptive mechanism for A. wenchowensis to cope with acute temperature changes. Through STEM analysis and the black WGCNA module associated with high-temperature stress, we identified significant up-regulation of pathways and hub genes related to energy metabolism including oxidative phosphorylation, TCA cycle, purine metabolism, and glutathione metabolism, as well as the central roles of signal transduction pathways such as MAPK signaling pathway and AMPK signaling pathway, which synergistically regulate energy production. Under acute low-temperature stress, the turquoise WGCNA module highlighted significant up-regulation of hub genes associated with Ribosomal and Spliceosomal pathways related to protein synthesis and processing, as well as activation of calcium signaling pathways, which plays an important role in maintaining cellular function during low-temperature adaptation. These findings provide a critical theoretical and molecular basis for the adaptation of eurythermal fish to rapid temperature changes.

Long-Term Warming of Baltic Sea Coastal Waters Affects Bacterial Communities in Bottom Water and Sediments Differently

Coastal marine ecosystems are some of the most diverse natural habitats while being highly vulnerable in the face of climate change. The combination of anthropogenic influence from land and ongoing climate change will likely have severe effects on the environment, but the precise response remains uncertain. This study compared an unaffected "control" Baltic Sea bay to a "heated" bay that has undergone artificial warming from cooling water release from a nuclear power plant for ~50 years. This heated the water in a similar degree to IPCC SSP5-8.5 predictions by 2100 as natural systems to study temperature-related climate change effects. Bottom water and surface sediment bacterial communities and their biogeochemical processes were investigated to test how future coastal water warming alters microbial communities; shifts seasonal patterns, such as increased algae blooming; and influences nutrient and energy cycling, including elevated respiration rates. 16S rRNA gene amplicon sequencing and geochemical parameters demonstrated that heated bay bottom water bacterial communities were influenced by increased average temperatures across changing seasons, resulting in an overall Shannon's H diversity loss and shifts in relative abundances. In contrast, Shannon's diversity increased in the heated surface sediments. The results also suggested a trend toward smaller-sized microorganisms within the heated bay bottom waters, with a 30% increased relative abundance of small size picocyanobacteria in the summer (June). Furthermore, bacterial communities in the heated bay surface sediment displayed little seasonal variability but did show potential changes of long-term increased average temperature in the interplay with related effects on bottom waters. Finally, heated bay metabolic gene predictions from the 16S rRNA gene sequences suggested raised anaerobic processes closer to the sediment-water interface. In conclusion, climate change will likely alter microbial seasonality and diversity, leading to prolonged and increased algae blooming and elevated respiration rates within coastal waters.

Tolerance to climate change of the clonally reproducing endemic Baltic seaweed, Fucus radicans: is phenotypic plasticity enough?

To predict the effects of climate change, we first need information on both the current tolerance ranges of species and their future adaptive potential. Adaptive responses may originate either in genetic variation or in phenotypic plasticity, but the relative importance of these factors is poorly understood. Here, we tested the tolerance of Fucus radicans to the combination of hyposalinity and warming projected by climate models for 2070-2099. We measured the growth and survival responses of thalli in both current and future conditions, focusing on variations in tolerance among and within different clonal lineages. Survival was 32% lower in future than in current conditions, but the weight and length of the thalli which survived was respectively 267% and 178% higher when exposed to future conditions. The relatively high tolerance to the future conditions suggests that F. radicans is likely to persist in its current distributional range, which is limited to the Gulf of Bothia and Estonian coast in the Baltic Sea. Furthermore, this species may be able to expand its distribution southward and replace its congener F. vesiculosus, which, in previous studies, has not tolerated the future conditions as well. In addition, we discovered variation in tolerance to future conditions within one of the clonal lineages, which have been hitherto presumed to lack adaptive variation. The discovery of intra-clonal phenotypic plasticity means that this alga has the potential for adaptive responses to climate change, which may be the key to the future persistence of F. radicans in the Baltic Sea.

Variation in salinity tolerance between and within anadromous subpopulations of pike (Esox 1ucius)

Environmental heterogeneity is a key determinant of genetic and phenotypic diversity. Stable and homogenous environments tends to result in evolution of specialism and local adaptations, while temporally unpredictable environments may maintain a diversity of specialists, promote generalist strategies, or favour diversified bet hedging strategies. We compared salinity tolerance between two anadromous subpopulations of pike (Esox Lucius) that utilize freshwater spawning sites with different salinity regimes. Eggs from each population were artificially fertilized and incubated in a salinity gradient (0, 3, 5, 7, and 9 psu) using a split-brood design. Effects on embryonic development, hatching success, survival of larvae, and fry body length were compared between populations and families. The population naturally spawning in the stable freshwater habitat showed signs of specialization for freshwater spawning. The population exposed to fluctuating selective pressure in a spawning area with occasional brackish water intrusions tolerated higher salinities and displayed considerable variation in reaction norms. Genetic differences and plasticity of salinity tolerance may enable populations to cope with changes in salinity regimes associated with future climate change. That geographically adjacent subpopulations can constitute separate units with different genetic characteristics must be considered in management and conservation efforts to avoid potentially negative effects of genetic admixture on population fitness and persistence.