Coral reefs are in trouble due to reasons both global (temperature stress, ocean acidification, increased disturbance) and local (overfishing, pollution). Many of these issues are likely to be exacerbated in the future by climate change.
Fortunately, many (although not all) coral reef ecosystems are under legal protection and located in climate refugia, enabling them to act as source populations for unprotected reefs. This ability to “rescue” other reefs depends to a large extent on how well connected reef networks are.
Greiner, A., Andrello, M., Darling, E., Krkošek, M. and Fortin, M.J. 2022. Limited spatial rescue potential for coral reefs lost to future climate warming. Global Ecology and Biogeography. DOI: 10.1111/geb.13571.
While several studies have looked at reef connectivity at the regional scale, less is known about reef connectivity at the global scale, even though decisions about reef management and conservation are influenced globally by climate change.
Stepping into this gap is a recent study that takes a global approach to figuring out which reefs are connected to which, how many different coral larval dispersal networks exist, and how big these larval dispersal networks actually are. Using a global coral larval dispersal model, three different levels of coral reef loss, followed by reseeding, were simulated to determine how well reefs might recover under the current reef network.
The analysis shows that there are over 600 networks of reefs across the oceans. The majority of these are small, and only a few are very large, such as the Great Barrier Reef and the Coral Triangle. Almost half of the world’s reef cells are in one connectivity network, with more than two-thirds contained in 14 large networks.
The most encouraging results show that in a scenario where most climate refugia are preserved, connectivity is still maintained even under high habitat loss, although reseeding reaches less than half the former reef habitat. Other scenarios of more random loss show a more unpredictable picture, with much lower connectivity throughout the network but widespread reseeding. The order in which coral reefs – and therefore network connectivity – are lost plays an important role in recovery.
There are several things to keep in mind to better manage and conserve coral reefs under the future climate. If global reef refugia remain (as predicted), then there is a chance that current connectivity will still be applicable in the future, even as habitat is lost. The idea of reseeding is also an important consideration, because simply prioritizing high connectivity or high coral cover levels might not simultaneously ensure high reseeding potential as well.
Once coral reefs are gone, it is unlikely they can be returned to their present state, even if a similar amount of habitat is inhabited again. Improved climate predictions, increased knowledge about coral larval dispersal, and a better understanding about how coral networks function can all help mitigate the consequences of climate change on one of the most diverse ecosystems on the planet.
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