Executive Summary

Coral reefs cover less than 1% of the ocean floor yet support up to 30% of all marine life (Plaisance et al., 2011) and generate US$6.8 billion in annual net profits from global fisheries (Burke et al., 2011). Reefs also help reduce coastal floods, saving US$1 billion per year in the US alone (Reguero et al., 2021), and attract US$36 billion in global tourism annually (Spalding et al., 2017). Since the 1950s, however, coral cover has declined due to overfishing, coastal development, and systemic increases in pollution and ocean temperature. By 2050, and without considering adaptation, 70% to 90% of coral reefs are likely to disappear, given a warming scenario of only 1.5 °C; with warming of 2 °C, 99% of all coral reefs will be lost in less than 30 years (IPCC, 2022). A new ‘30x30’ COP15 initiative aims to protect 30% of the world’s land, freshwater, and sea areas by the year 2030 (CBD, 2022). This effort strives to safeguard ecosystems that are biologically essential due to the goods and services they provide, in addition to maintaining a diverse range of habitat types. Coral reefs provide a myriad of ecological benefits to ocean and coastline communities, including human populations, and are noted as a critical ecosystem to prioritise (ICRI, 2022).

Protection in this context is multifaceted and entails:

• Mitigating impacts on global (e.g., reduction of greenhouse gas emissions) and local (e.g., management of water quality and invasive species) scales (Mumby & Steneck, 2008).

• Increasing the success of programmes to restore degraded reefs (Knowlton et al., 2021; National Academies of Sciences & Medicine, 2019).

• Identifying coral populations that are resistant or that might recover rapidly after heat stress events (ICRI, 2022).

• Understanding how to assist corals with adaptation to ocean warming (Baums et al., 2019; Goergen et al., 2020; Shaver et al., 2022).

Substantial investment, such as through the Reef Restoration and Adaptation Program (RRAP), the Defense Advanced Research Projects Agency (DARPA), and the Coral Research & Development Accelerator Platform (CORDAP) is needed to support Research & Development (R&D) for novel natural resource management tools that enhance the capacity of corals to adapt to climate change (i.e., assisted evolution; van Oppen et al. 2015). Assisted evolution refers to human actions seeking to accelerate the rate of evolutionary processes within populations or species to help them adapt to a changing environment. Over recent years the number of studies on the assisted evolution of corals has increased dramatically, with most able to demonstrate enhanced tolerance of the coral holobiont (that is, the cnidarian host, the photosynthetic symbionts and other microbes), (Drury et al., 2022 and more). Yet significant knowledge gaps exist in our fundamental understanding of how coral heat tolerance evolves and the efficacy or effect size of interventions that aim to improve this process. Further, the technologies or strategies to implement these approaches at scale are largely absent in both restoration and adaptation contexts. As a result, resources including funding and time cannot be applied effectively and strategically. To address these issues, we evaluated gaps in knowledge about coral thermal adaptation and the interventions used to enhance their tolerance and adaptation to global heating.

Specifically, we:

1. Systematically reviewed studies published between 1975 and 2022 on the responses of corals, their microalgal symbionts (hereafter called symbionts), or bacterial microbiota (hereafter referred to as microbes) to heat stress either under laboratory conditions or during marine heatwaves. We compiled studies into a database, which we used to objectively examine what is known about the potential for natural adaptation of corals to increased temperatures and the effect sizes of assisted evolution efforts that have been documented to date.

2. Obtained the expert opinions of 22 coral reef scientists currently leading research and development on assisted evolution and six evolutionary biologists via a 3-day workshop at King Abdullah University of Science and Technology (KAUST) in Saudi Arabia (24 - 26 January 2023), as well as via pre- and post-workshop questionnaires. In doing so, we identified gaps in fundamental knowledge of coral evolution and established priorities for knowledge acquisition relevant to using management strategies that aim to increase adaptive resilience.

3. Prepared a report and synthesised findings into a Roadmap using the systematic review of the literature, questionnaires, and workshop discussions. The recommendations for funding prioritisation that we provide here were informed by the participants of the workshop, a review of the literature, and weekly discussions amongst the ten participants comprising the core group.