The Future of Coral Reefs Subject to Rapid Climate Change: Lessons from Natural Extreme Environments

Abstract

Global climate change and localized anthropogenic stressors are driving rapid declines in coral reef health. In vitro experiments have been fundamental in providing insight into how reef organisms will potentially respond to future climates. However, such experiments are inevitably limited in their ability to reproduce the complex interactions that govern reef systems. Studies examining coral communities that already persist under naturally-occurring extreme and marginal physicochemical conditions have therefore become increasingly popular to advance ecosystem scale predictions of future reef form and function, although no single site provides a perfect analog to future reefs. Here we review the current state of knowledge that exists on the distribution of corals in marginal and extreme environments, and geographic sites at the latitudinal extremes of reef growth, as well as a variety of shallow reef systems and reef-neighboring environments (including upwelling and CO 2 vent sites). We also conduct a synthesis of the abiotic data that have been collected at these systems, to provide the first collective assessment on the range of extreme conditions under which corals currently persist. We use the review and data synthesis to increase our understanding of the biological and ecological mechanisms that facilitate survival and success under sub-optimal physicochemical conditions. This comprehensive assessment can begin to: (i) highlight the extent of extreme abiotic scenarios under which corals can persist, (ii) explore whether there are commonalities in coral taxa able to persist in such extremes, (iii) provide evidence for key mechanisms required to support survival and/or persistence under sub-optimal environmental conditions, and (iv) evaluate the potential of current sub-optimal coral environments to act as potential refugia under changing environmental conditions. Such a collective approach is critical to better understand the future survival of corals in our changing environment. We finally outline priority areas for future research on extreme and marginal coral environments, and discuss the additional management options they may provide for corals through refuge or by providing genetic stocks of stress tolerant corals to support proactive management strategies.

Mangrove lagoons of the Great Barrier Reef support coral populations persisting under extreme environmental conditions

“…Inshore reefs of the GBR attenuate solar irradiance that otherwise can exacerbate thermal stress, resulting in reduced bleaching severity and sustained coral cover post-bleaching (Morgan et al 2017). While refugia will contribute to aiding some coral populations through periods of stress, their temporal and spatial restrictions, combined with the fact that most refugia only offset a single stressor (reviewed by Camp et al 2018b), means that there is arguably a more time-critical need to identify and study naturally resilient coral populations in order to (1) understand which coral species can best survive multiple stressors, (2) identify the key mechanisms that support coral survival and (3) reveal any associated biological and ecological costs to corals with enhanced stress tolerance. Such knowledge can aid decisions that currently need to be made regarding which species should be targeted for restoration and adaptive management options (e.g.…”

Coral bleaching patterns are the outcome of complex biological and environmental networking

“…Classic single factor experiments have been central to isolate mechanistic biological pathways or the response of ecological outcomes to any one factor. However, single factor perturbations are not representative of the complex biogeochemistry of reef habitats or indeed future climate scenarios (see Camp, Schoepf, Mumby, et al, ), so much so that they may mis‐inform as to how successfully taxa tolerate multifactor interactions. For example, corals adapted to tolerate enhanced CO 2 have been shown to downregulate molecular chaperones that would ultimately enhance heat stress sensitivity (Kenkel, Moya, Strahl, Humphrey, & Bay, ).…”

“…(e.g., Camp, Schoepf, & Suggett, ). Developing tools that can identify coral populations with enhanced stress tolerance (Baums et al, ; Morikawa & Palumbi, ) or indeed the complex environmental networks that precondition enhanced survival (Camp, Schoepf, Mumby, et al, ) are undoubtedly a priority. Using knowledge of site‐specific differences in thermal histories has indeed proven central in the success of propagating coral populations more resistant to thermally induced bleaching (Morikawa & Palumbi, ), but how this can further scale to include other factors moderating bleaching severity will require more advanced environmental assessment capability.…”

bg-2018-57 - Author response to Reviewers comments

“…, while the mean calculated pCO2 (414 to 468 µatm, Table 1) is similar in this comparison, and also 356 near the reported atmospheric values (accessed November 2017: 405.58 µatm pCO2; NOAA/Earth System Research 357 Laboratory). The high Ωa can be attributed to the salinity and AT of the Red Sea, ranging from 2346 -2429 µmol kg -1 358 (Table 1), supporting the notion that Red Sea reefs could be a refuge for reef-building corals under climate change 359 with respect to ocean acidification (OA)(Camp et al, 2018). To test the hypothesis whether Red Sea reefs will reach 360 a critically low Ωa later, and maintain a calcification-friendly sea water chemistry on longer terms, compared to other 361 tropical reef regions under OA, an experimental approach and a high precision and high resolution monitoring of reef 362…”