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Deep corals are no refuge for fish fleeing pollution, says study



Deep coral reefs in a "twilight zone" in the oceans are very different from those near the surface and dampen hopes that they will be a refuge for marine life fleeing threats such as climate change and pollution.

A US-led team of divers who studied lesser-known reefs in the Western Atlantic and Pacific Ocean between 100 to 500 feet deep where sunlight was dying, found most species of coral and fish different from those closer located on the surface.

"We were surprised to find little overlap," said lead author Luiz Rocha of the California Academy of Sciences Reuters of the results published in the journal Science . Less than five percent of the fish and corals were found in shallow and deep waters, against the scientists' previous estimate of 60 to 75%, based on historical records,

"The potential for deep reefs to act in a refuge capacity much less than we had previously hoped, "they wrote. And like deep reefs, deep reefs also faced threats such as climate change, storms and pollution. Divers found, for example, plastic fishing nets caught in deep coral off the Philippines and deep coral damaged by warm waters off the Bahamas.

Deep Reef Protection

Rocha said scientists were trying to place temperature sensors at dusk to see how far deep reefs were exposed to rising ocean temperatures, which are most extreme on the surface. Deep reefs covered at least the same marine area worldwide as shallow reefs, he estimated. Some reefs, such as those off the mouth of the Amazon, exist only in depth. The authors called for better safety measures for deep reefs, for example by developing protected areas and banning trawl nets that can scrape the seabed.

A study by the United Nations Environment Program in 201

6 showed that some deep reefs could function as what it called "lifeboats" for nearby, shallower reefs. But it said that in other cases deep reefs could be "as vulnerable as flatter reefs" to human pressure.


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