Coral reefs may survive bleaching in deeper environments

Sydney: Offering a glimmer of hope to those managing the impact of bleaching on the world's coral reefs, a new UN report has found that part of the ecosystem may survive in barely known deeper environments, known as mesophotic coral ecosystems (MCEs). Coral bleaching has affected virtually the entire Great Barrier Reef and many other coral reef systems globally, including those of the Lakshadweep islands of India -- a result of the continuing rise in global temperatures and exacerbated by the summer's major El Nino event. The United Nations Environmental Programme report released on Tuesday said that as the world's surface reefs are being threatened, part of the ecosystem may survive in these mesophotic coral ecosystems. Shallow coral reefs from the water's surface to 30-40 metres depth are the tip of the iceberg that comprises the ocean's extensive coral ecosystem. Mesophotic coral ecosystems are intermediate depth reefs starting at about 40 metres depth and continuing to around 150 metres.  The report looked at the role mesophotic coral ecosystems could play in the preservation of shallower reefs -- whether they can provide a refuge for the species under threat in shallower reef ecosystems and whether they can provide the stock to re-populate shallow reefs if they continue to decline. "Mesophotic coral ecosystems are a seed bank for some organisms," said one of the study authors Elaine Baker from University of Sydney in Australia. "More research needs to be done to firmly establish the role of MCEs in preserving our reefs; they aren't a silver bullet but they may be able to resist the most immediate impacts of climate change -- thereby providing a refuge for some species and potentially helping to replenish destroyed surface reef and fish populations,” Baker said in a university statement. "It may be that the cooler, deeper water in MCEs could be more hospitable to many species than the warmer surface water," she said.  The review brought together information on the geology, biology, distribution and socio-economic aspects of mesophotic reefs in order to examine their potential resilience. "They also are less prone to waves and turbulence, therefore potentially offering a more stable environment," Baker noted. The report found some deep mesophotic coral ecosystems may be less vulnerable to the most extreme ocean warming, but others may be just as vulnerable as their shallow counterparts and cannot be relied on to act as "life boats".