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The deep sea plays a critical role in global climate regulation through uptake and storage of heat and carbon dioxide. However, this regulating service causes warming, acidification and deoxygenation of deep waters, leading to decreased food availability at the seafloor. These changes and their projections are likely to affect productivity, biodiversity and distributions of deep-sea fauna, thereby compromising key ecosystem services. Understanding how climate change can lead to shifts in deep-sea species distributions is critically important in developing management measures. We used environmental niche modelling along with the best available species occurrence data and environmental parameters to model habitat suitability for key cold-water coral and commercially important deep-sea fish species under present-day (1951-2000) environmental conditions and to project changes under severe, high emissions future (2081-2100) climate projections (RCP8.5 scenario) for the North Atlantic Ocean. Our models projected a decrease of 28%-100% in suitable habitat for cold-water corals and a shift in suitable habitat for deep-sea fishes of 2.0°-9.9° towards higher latitudes. The largest reductions in suitable habitat were projected for the scleractinian coral Lophelia pertusa and the octocoral Paragorgia arborea, with declines of at least 79% and 99% respectively. We projected the expansion of suitable habitat by 2100 only for the fishes Helicolenus dactylopterus and Sebastes mentella (20%-30%), mostly through northern latitudinal range expansion. Our results projected limited climate refugia locations in the North Atlantic by 2100 for scleractinian corals (30%-42% of present-day suitable habitat), even smaller refugia locations for the octocorals Acanella arbuscula and Acanthogorgia armata (6%-14%), and almost no refugia for P. arborea. Our results emphasize the need to understand how anticipated climate change will affect the distribution of deep-sea species including commercially important fishes and foundation species, and highlight the importance of identifying and preserving climate refugia for a range of area-based planning and management tools.

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Deep-sea sponge grounds are distributed globally and are considered hotspots of biological diversity and biogeochemical cycling. To date, little is known about the environmental constraints that control where deep-sea sponge grounds occur and what conditions allow high sponge biomass to develop in the deep sea. Here, we characterize oceanographic conditions at two contrasting high- and low-sponge-biomass sites off the northern Labrador Shelf in Canadian waters. Unique data for the region were collected by year-long benthic lander deployments equipped with current meters, turbidity and chlorophyll-a sensors, and sediment traps. Additionally, the regional oceanography was described by analysing vertical conductivity/salinity-temperature-depth (CTD) and Argo float profiles for the Northern Labrador Shelf from 2005 to 2022, including those from the CTD casts taken at the benthic lander stations. Benthic fauna stable isotopes were analysed to identify potential food sources. Our results revealed strong (0.26 ± 0.14 m s-1; mean ± SD) semidiurnal tidal currents at the high-sponge-biomass site, but twofold weaker currents (0.14 ± 0.08 m s-1; mean ± SD) at the low-sponge-biomass site. These tidal currents cause periodic temperature fluctuations, sediment resuspension, intense vertical flows across the slope, which during spring, contribute to transport of organic material to the seafloor during a diurnal tidal cycle. Periodic fluctuations in bottom water temperature confirm the amplified transport across the shelf break at the high-sponge-biomass site. The high-sponge-biomass area is situated where the Hudson Strait Ouflow, the Irminger Current, and the West Greenland Current converge, which could lead to downwelling. Bottom silicate concentrations were increased at the high-biomass sponge ground due to advection of silicate-rich bottom water from Baffin Bay. Finally, the arrival of chlorophyll-a rich material in spring at both the low- and high-sponge-biomass sites demonstrated tight benthic-pelagic coupling prior to the onset of stratification. Mass fluxes of trapped material were higher and consisted of less degraded material at the high-sponge-biomass site. Stable isotope signatures indicated that soft corals (Primnoa resedaeformis) fed on suspended particulate organic matter, while massive sponges (Geodia spp.) likely utilized additional food sources. Our results imply that benthic fauna at the high-sponge-biomass site benefit from strong tidal currents, which increases food supply, and favourable regional ocean currents that increase nutrient concentration in bottom waters. [ABSTRACT FROM AUTHOR]

Epigenetic modifications are thought to be one of the molecular mechanisms involved in plastic adaptive responses to environmental variation. However, studies reporting associations between genome-wide epigenetic changes and habitat-specific variations in life history traits (e.g. lifespan, reproduction) are still scarce, likely due to the recent application of methylome resequencing methods to non-model species. In this study, we examined associations between whole genome DNA methylation and environmentally driven life history variation in 2 lineages of a marine fish, the capelin (Mallotus villosus), from North America and Europe. In both lineages, capelin harbor 2 contrasting life history tactics (demersal vs. beach-spawning). Performing whole genome and methylome sequencing, we showed that life history tactics are associated with epigenetic changes in both lineages, though the effect was stronger in European capelin. Genetic differentiation between the capelin harboring different life history tactics was negligible, but we found genome-wide methylation changes in both lineages. We identified 9,125 European and 199 North American differentially methylated regions (DMRs) due to life history. Gene ontology (GO) enrichment analysis for both lineages revealed an excess of terms related to neural function. Our results suggest that environmental variation causes important epigenetic changes that are associated with contrasting life history tactics in lineages with divergent genetic backgrounds, with variable importance of genetic variation in driving epigenetic variation. Our study emphasizes the potential role of genome-wide epigenetic variation in adaptation to environmental variation. [ABSTRACT FROM AUTHOR]