Juvenile corals provide glimpse into recovery of coral reef after devastating bleaching event |22 December 2021

Research diver counting the number of juvenile corals within a quadrat © Cheryl Sanchez, Courtesy of the Seychelles Islands Foundation

As the world’s oceans warm, research on coral reproduction and growth, particularly after coral bleaching, is urgently needed to be able to identify solutions and hope spots for coral reef conservation.

A study published on Tuesday December 7 in PLOS ONE by researchers from the University of Bremen and the Seychelles Islands Foundation (SIF), gives new insights into the number of coral juveniles following a coral bleaching event at Aldabra Atoll.

The paper entitled ‘First insights into coral recruit and juvenile abundances at remote Aldabra Atoll, Seychelles’, led by recent University of Bremen PhD graduate and current Aldabra Marine Researcher Dr Anna Koester, and co-authored by SIF’s Dr Nancy Bunbury and former Aldabra Science Coordinator, Cheryl Sanchez, presents new findings on how quickly coral communities can rebound after bleaching. Juvenile corals were found to increase rapidly following the 2015/16 bleaching event, with their numbers more than doubling between 2016 (immediately after the bleaching) and 2019.

“The abundance of coral juveniles is a good indicator for the recovery of coral reefs following disturbances such as coral bleaching,” Dr Koester said, and went on to explain, “Coral juveniles, which are small immature coral colonies, can suffer from coral bleaching as severely as their adult counterparts and can experience major die-offs. However, bleaching also affects reproduction of adult corals, so that even several years after bleaching, coral reproduction, and therefore the abundance of young corals, can be suppressed. The increase in coral juveniles we report is therefore a promising sign for the recovery of Aldabra’s reefs and complements the findings of our previous work (Early trajectories of benthic coral reef communities following the 2015/16 coral bleaching event at remote Aldabra Atoll, Seychelles, 2020; https://www.nation.sc/articles/6434/new-research-reveals-aldabras-coral-reef-resilience-and-recovery-capacity)”.

To improve the understanding of coral reproduction at Aldabra, the researchers also measured abundance of newly settled coral larvae and found that coral spawning at Aldabra peaked between October and December.

“Before this research, we only had a rough idea of when coral spawns at Aldabra, really an informed guess based on research from the Inner Seychelles and wider region,” Dr Bunbury said.

She added, “This finding, coupled with emerging new data on the prevailing currents during October–December, and concurrent coral genetic research, will shed light on the connectivity of coral reefs in the region, for example, which reefs receive coral larvae from Aldabra and therefore directly benefit from the protection of this Unesco World Heritage Site”.

The authors note that further work is needed to confirm the observed patterns, but highlight that this research is the first published record on coral larvae settlement in the Seychelles Outer Islands. As such, the findings are much-needed for understanding both the process and prospects of bleaching recovery and resilience of remote reefs. With severe bleaching events projected to occur annually for 90% of the world’s coral reefs by 2055, such research and long-term commitment to monitoring these priceless ecosystems and the connectivity between them is critical. Through their annual Aldabra Reef Monitoring programme, SIF is in a position to supply science of global significance to contribute to the world’s adaptation to a new climate reality.

Full paper reference:  Koester, A., Ford, A. K., Ferse, S. C. A., Migani, V., Bunbury, N., Sanchez, C., and Wild, C. 2021. First insights into coral recruit and juvenile abundances at remote Aldabra Atoll, Seychelles. PLoS ONE 16(12): e0260516. https://doi.org/10.1371/journal.pone.0260516

The paper is available open access: https://doi.org/10.1371/journal.pone.0260516

Press release from the Seychelles Islands Foundation