25 September: Coral recovery on the isolated reefs of the Keppel Islands

How do corals recover after a major loss? There are several possibilities. Surviving coral colonies can reproduce and repopulate the local area with their own coral recruits. Alternatively, populations can recover if new coral recruits flow in from other reefs.

But what if there aren’t many external recruits, or there are so few corals left on the reef that their reproductive effort is insufficient to re-establish a viable community?

Coral reefs in the Keppel Island archipelago off the coast of Queensland in Australia are helping to answer just that question. Here, recovery of the fast-growing coral, Acropora millepora, was found to occur mostly via regrowth of small amounts of coral tissue that survived a disturbance event, that were able to regrow over the apparently ‘dead’ coral skeleton. This discovery was made by Prof Madeleine van Oppen, Senior Principal Research Scientist at the Australian Institute of Marine Science and Professor at the University of Melbourne, along with collaborators from several Australian universities. Using genetic analysis, the team was able to identify that the overwhelming majority of coral recovery comes from corals already present in the Keppels.

Their findings are important because coral reefs in the Keppels are subject to frequent disturbances, including flooding, strong winds and, during summer, periods of above-average temperatures that can bleach and all but kill off the corals.

“This means that corals at the Keppels have a high conservation value – if none survive there is little chance of other reefs repopulating the archipelago”, says van Oppen.

In an interesting twist to the story, scientists found that the nature of recovery somewhat depended on the type of disturbance the Keppels’ reefs experience. Bleaching events, which tended to cause massive mortality across all reefs meant that corals recovered by tissue regrowth. After flooding events, however, coral loss varied among reefs, meaning that the healthier reefs in the archipelago could still supply significant numbers of coral recruits to recolonise devastated areas.

The paper, A population genetic assessment of coral recovery on highly disturbed reefs of the Keppel Island archipelago in the southern Great Barrier Reef, by Madeleine van Oppen, Vimoksalehi Lukoschek, Ray Berkelmans, Lesa Peplow and Alison Jones, was recently published in the journal PeerJ (DOI 10.7717/peerj.1092).