A quarter century after the 1998 El Niño, it is still difficult to predict how individual reefs will respond to recurring disturbances. Reports differ on the relative importance of anthropogenic influences, local geography and bleaching recurrence in determining resistance and recovery. It is assumed that coral traits largely determine winners and losers, based on bleaching susceptibility, recruitment, survival and growth. Whether this translates to the long-term fates of corals on reefs is still debated. We tracked multi-decadal coral compositional changes in reefs across the densely populated Lakshadweep Archipelago to explore how global bleaching events and local geographical factors (depth and wave exposure) influenced responses to repeated mass bleaching. Coral resistance increased with recurrent bleaching, uninfluenced by local geography. However, wave exposure regimes positively influenced recovery rates, given sufficient time between mortality events (>7 years). The overall trajectory though, was of protracted decline interspersed with periods of halting recovery, with many losers, and few resistant genera that lose less. Based on these responses, we identified six community clusters that describe contrasting long-term responses to local and global factors. Interestingly, genera with different functional traits cluster together, sharing similar fates, as a result of complex interactions between bleaching susceptibility, local geography and inter-bleaching intervals. These clusters provide a clear site-specific predictive framework of long-term community change, indicating that geography, community and time largely determine local responses to climate disturbances.

Thermal adaptation of organisms is a property emerging from the complex interplay of biophysical constraints and selective forces. The shape of thermal performance curves has been well investigated but we lack knowledge of how they may evolve. Two extreme cases can be expected: i) under the hypothesis of local adaptation, species should shift their thermal performance curves and have an optimum at the temperature at which they evolve, or ii) under the hypothesis of thermodynamical constraints, universal biophysical rules dictate a fixed performance curve with an optimum at warm temperatures. We perform an evolutionary experiment to test these two hypotheses on the thermal response of bacteria growth rate, expecting a strong evolutionary response of the thermal performance curve. We use four wild bacterial strains and allow them to evolve at ten different temperatures (ranging from 8.5 to 40°C) to subsequently measure their growth rate at these ten temperatures. We investigate the difference in growth rate between evolved lines and their ancestors. We observe signs of adaptation, as growth rates of evolved and ancestral strains exhibit small but significant differences. Our analysis shows however that the shape of the thermal performance curves does not systematically vary between evolved and ancestral strains, and none of the evolved lines have an optimal growth rate at the evolution temperature. One strain grows significantly faster than its ancestor at the temperature of evolution, but we find that for other strains, evolution leads to faster as well as slower growth rates. These differences are repeated between evolutionary replicates, suggesting they are selected. Our study demonstrates that adaptation does not always overcome thermodynamical constraints on growth rates, and helps to better understand how microbes will respond to temperature changes.

Marine ice is retreating in many sectors of Earth’s polar and subpolar regions. The rates are unprecedented, generating great concern in both scientific and public communities. Despite the expected serious implications, we lack a comprehensive understanding of how ice loss and related processes control marine biota and interactions at different spatiotemporal scales under multiple environmental stressors and drivers of change. We systematically review existing knowledge on how the losses of ice shelves, sea ice, and glaciers affect polar marine biocenosis. We include in situ, remote sensing, and modelling studies on sea ice biota, phyto- and zooplankton, fish, seabirds, phyto- and zoobenthos and marine mammals, covering a time span of three decades (1991-2022). We apply a qualitative ecosystem‐based risk assessment to assess the individual and cumulative response of ecosystem components and related ecosystem services. The most threats and opportunities are expected to manifest in the shallow coastal zones. They include loss of ice habitat, water column darkening due to sediment input with meltwater, increased sedimentation rates, and mechanical damage due to ice scouring, but also gain of marine habitat, lightening of the water column and nutrient input with meltwater. The cumulative score of all the stressors shows that marine ice loss will lead to autotroph-dominated polar marine systems with detrimental effects on secondary producers, i.e. zooplankton and zoobenthos, and sea ice-obligate species. Although similar stressors are recognised for polar and subpolar regions, some processes may differ in magnitude. This overview aims to provide summarised knowledge to inform science-based solutions for conservation and climate mitigation actions.