Coral-bleaching responses to climate change across biological scales

Abstract

The global impacts of climate change are evident in every marine ecosystem. On coral reefs, mass coral bleaching and mortality have emerged as ubiquitous responses to ocean warming, yet one of the greatest challenges of this epiphenomenon is linking information across scientific disciplines and spatial and temporal scales. Here we review some of the seminal and recent coral-bleaching discoveries from an ecological, physiological, and molecular perspective. We also evaluate which data and processes can improve predictive models and provide a conceptual framework that integrates measurements across biological scales. Taking an integrative approach across biological and spatial scales, using for example hierarchical models to estimate major coral-reef processes, will not only rapidly advance coral-reef science but will also provide necessary information to guide decision-making and conservation efforts. To conserve reefs, we encourage implementing mesoscale sanctuaries (thousands of km² ) that transcend national boundaries. Such networks of protected reefs will provide reef connectivity, through larval dispersal that transverse thermal environments, and genotypic repositories that may become essential units of selection for environmentally diverse locations. Together, multinational networks may be the best chance corals have to persist through climate change, while humanity struggles to reduce emissions of greenhouse gases to net zero.

Keywords: climate change; conservation; coral bleaching; coral reefs; corals; global warming; mesoscale sanctuaries; networks; protected reefs; refugia; thermal stress.

FIGURE 1

Global coral bleaching from 1980 to 2020. Coral bleaching was calculated as a percentage of the coral colonies that were bleached at the time of survey, from 11,068 sites in 89 countries (n = 23,298; data from van Woesik & Kratochwill, 2022)

FIGURE 2

The diversity of approaches used to investigate coral bleaching across spatial and biological scales

FIGURE 3

Coral responses to thermal stress at different temporal and biological scales. (a) Coral community response, reflected as overall living–coral coverage, to thermal stress and its hypothetical potential to adapt to future thermal stress; (b) Individual responses to thermal stress, showing characteristic responses of photosynthesis, calcification, reproduction, and lipid reserves; (c) Cellular responses of corals to thermal stress, where gene expression is typically considered to translate the encoded genomic potential into the resultant phenotype through proteins being expressed that in turn underlie the measured physiological change. In (a) the terms “with adaptation” and “no adaptation” refer to the potential of corals to adapt, considering both potential societal (i.e., reductions in emissions of greenhouse gases) and evolutionary (i.e., increases in thermal tolerance) adjustments