The secret to saving our coral reefs may lie in sea cucumbers

Although the humble sea cucumber may not look like much, it could soon be enlisted to help save the world's coral reefs. It has been found that bottom-dwelling animals play a vital role in protecting coral reefs from harmful bacteria.

Climate change is largely responsible for the mass death of our planet's coral reefs, as stress from rising water temperatures causes corals to expel the symbiotic algae that live within them. But the loss of these life-giving algae is not the only problem.

Stressed corals are also more susceptible to infection by naturally occurring bacteria. In the past, populations of these microbes were maintained at manageable levels by sea cucumbers, which feed on seafloor sediments. Unfortunately, due to over-harvesting for use in the Asian seafood market, sea cucumbers are now increasingly rare in many regions.

In order to learn how important animals are to coral reef health, the Georgia Tech team led by Mark Hay and Cody Clements conducted a series of field experiments in the South Pacific Ocean.

Aerial view of Holothuria atra Sea cucumbers near Moorea Island – This species has little commercial value, so it is abundant in the area

Dr. Cody Clements is a research scientist, College of Biological Sciences, Georgia Institute of Technology, Atlanta

And near the island of Moorea in French Polynesia, scientists remain Holothuria atra Sea cucumbers in 10 plots of sandy seabed, removed them from 10 other plots, then planted five of them Acropora pulcra Coral slices in both plots. These pieces were then inspected daily for 45 days. It was ultimately found that coral mortality from sediment-related diseases was 15 times greater in plots without sea cucumbers.

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The researchers obtained similar results when they conducted a similar experiment on a smaller scale on Palmyra Atoll, which is located between Hawaii and American Samoa. But this time, they used different types of sea cucumbers (Stecopus cleronotus) and coral (Acropora nasota).

Cody Clements first became aware of the beneficial impact of sea cucumbers when he noticed the failure of coral restoration efforts in areas where he had removed the creatures.
Cody Clements first became aware of the beneficial impact of sea cucumbers when he noticed the failure of coral restoration efforts in areas where he had removed the creatures.

Dr. Cody Clements is a research scientist, College of Biological Sciences, Georgia Institute of Technology, Atlanta

Hay and Clements now hope their findings will prompt governments and other groups to impose tougher restrictions on sea cucumber harvesting, and to begin breeding the animals to release on coral reefs in need of protection. Farmed sea cucumbers could also potentially be used to keep fish farms clean, perhaps even delaying the onset of type 2 diabetes.

“If you remove all the scum from a large aquarium on the floor, you will end up with a dirty tank,” Clements said. “People have been talking about the idea that sea cucumbers could be important for a long time, but we didn't know how important they were until now.”

A research paper was recently published in the journal Nature Communications.

sources: Georgia Tech, SciDev.Net website

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