Marginal reefs under stress: physiological limits render Galápagos corals susceptible to ocean acidification and thermal stress

Abstract

Ocean acidification (OA) and thermal stress may undermine corals’ ability to calcify and support diverse reef communities, particularly in marginal environments. Coral calcification depends on aragonite supersaturation (Ω » 1) of the calcifying fluid (cf) from which the skeleton precipitates. Corals actively upregulate pHcf relative to seawater to buffer against changes in temperature and dissolved inorganic carbon, which together control Ωcf. Here we assess the buffering capacity of modern and fossil corals from the Galápagos Islands that have been exposed to sub-optimal conditions, extreme thermal stress, and OA. We demonstrate a significant decline in pHcf and Ωcf since the pre-industrial era, trends which are exacerbated during extreme warm years. These results suggest that there are likely physiological limits to corals’ pH buffering capacity, and that these constraints render marginal reefs particularly susceptible to OA.

Plain Language Summary

Reef-building corals regulate their internal environment to permit rapid growth, which is critical for creating the structure and function of coral reefs. However, we demonstrate that there are finite limits to the ability of corals to regulate their internal chemistry to optimize growth. This limitation will leave corals susceptible to ocean warming and acidification, particularly in sub-optimal environments. Galápagos corals already display signs of stress and an inability to maintain an optimal internal growth environment from the eighteenth century to today.

Thompson D., McCulloch M., Cole J. E., Reed E. V., D’Olivo J. P., Dyez, K., Lofverstrom M., Lough J., Cantin N., Tudhope A. W., Cheung A. H., Vetter L. & Edwards R. L., 2022. Marginal reefs under stress: physiological limits render Galápagos corals susceptible to ocean acidification and thermal stress. AGU Advances 3(1): e2021AV000509. doi: 10.1029/2021AV000509. Article.


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