With more than 60% of reefs under threat from human activity, it's time to step up efforts to identify and protect deeper coral reefs to provide a refuge for fish and corals that can live there, say scientists.
Many reef species which inhabit shallow waters are also to be found on reefs at depths of 30 m or more, amid lower light conditions. This makes these deep reefs a potential refuge for both corals and other sea life when shallow reefs are degraded.
Marine scientists from Australia and the USA today called for global efforts to protect deeper coral reefs as insurance against the widespread destruction of shallow reefs and their fish stocks now taking place around the world.
Dr. Tom Bridge from the ARC Centre of Excellence for Coral Reef Studies based at James Cook University and colleagues point out that global conservation policies have so far failed to prevent the widespread destruction of coral reefs and their fish life, which now threatens the food security of millions of people.
"We recommend acting quickly, because pressure to over-exploit deep reefs will inevitably grow as shallow reefs become almost universally degraded due to growing human population pressures and climate change," says co-author Dr. John Guinotte from the Marine Conservation Institute.
"In China, coastal development and overfishing has destroyed 80% of coral cover in just the past 30 years. In Australia, coral cover on coastal reefs is also plummeting and the World Heritage Listing of the Great Barrier Reef (GBR) is now under review."
However, worldwide there is only a patchy record of where these deeper reefs are located, making their protection problematic.
"The area of these deep reefs may in fact be quite large. On the GBR recent surveys have revealed up to 20,000 square kilometres of deep reef – equal in size to the combined area of all the shallow reefs," Dr. Bridge says.
"While many species inhabit both shallow and deeper waters, the extent to which this occurs is as yet poorly understood. However they may form an important source of replenishment for shallow reefs and their fish stocks, given the destruction that is occurring on these reefs themselves and in the surrounding mangroves and sea-grass beds which are a nursery for juvenile fish."
At present very few of these deeper reef systems receive any form of protection around the world because reef management — where it exists — tends to focus on shallow reefs, the scientists say. Mid-level and deeper reefs are not generally included in Marine Protected Areas — an oversight that needs to be amended.
"The economic and conservation value of deeper reefs renders them worthy of protection in their own right, and safeguarding these habitats will also extend ongoing efforts in shallow water to protect reef species across their entire depth range," says Dr. Bridge.
The article appears in the journal Nature Climate Change.
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