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Indian Ocean’s Coral Reefs Face Uncertain Future as Oceanic Heat Content Continues to Rise

A recent study has revealed that a significant portion of the global oceanic heat content increase over the past two decades can be attributed to just one quarter of the world’s oceans, despite making up only 13% of the global ocean surface.

The Indian Ocean Region: A Hotspot for Coral Bleaching

In the Indian Ocean region, coral reefs have faced multiple bleaching events since the 1998 event. While some reefs have shown resilience, others have suffered devastating impacts on community composition and reef carbonate production. The 2015-2016 bleaching event had a major impact on many reefs, with mortality of tabular Acropora spp. leading to a decline in coral cover and associated decrease in mean reef rugosity.

Challenges Facing Coral Reefs

Reef degradation due to intense external and internal bio-physical erosion is likely to continue for several years, affecting not only the health of reefs but also their ability to provide important habitat for diverse species.
Structural complexity remains a significant concern, making it essential to employ innovative methods such as “structure from motion” photogrammetry techniques to accurately capture 3D reef structure and monitor changes.

Mesophotic Coral Ecosystems: A Neglected Frontier

The Indian Ocean region is home to a diverse array of coral ecosystems, including mesophotic coral ecosystems (MCEs) found at depths of 30 m to >150 m. These ecosystems are poorly studied and require further research to understand their resilience to climate change.

Prioritizing Conservation Efforts

As the ocean continues to warm, with associated decreases in oxygen concentrations and pH levels, it is crucial to consider the local variation in vulnerability of reefs to these changes. Finer-resolution models are being developed to identify relative vulnerabilities of coral reefs across the Indian Ocean, which will inform further research on their resilience.

Resilience factors, including heat stress tolerance, genetic diversity, and connectivity between shallow and mesophotic reefs, will be crucial in determining the fate of these ecosystems.
Conservation efforts should prioritize the preservation of coral reefs to ensure their long-term survival.

Sources

Beal et al. (2020) Oceanic Heat Content Increase Over the Past Two Decades
Roxy et al. (2020) Tropical Indian Ocean Sea Surface Temperatures
Perry et al. (2015) Carbonate Budget of Coral Reefs
Lange et al. (2020) Reef Growth Potential and Geo-Ecological Services
Bayley et al. (2019) Structure from Motion Photogrammetry Techniques
Graham and Nash (2013) Fish Abundance and Diversity on Coral Reefs
Turner et al. (2017) Mesophotic Coral Ecosystems
Andradi-Brown et al. (2019) Multibeam Surveys of Mesophotic Communities
Hays et al. (2020) Preliminary Analysis of Mesophotic Corals
Foster and Howell (unpublished data) Molecular Analysis of Scleractinian Coral Specimens