October 21 2011,

Georgia Tech's Douglas Rasher prepares coral for experiments in Fiji. Photograph courtesy M.E. Hay

The growing list of things damaging coral reefs just got longer as a new study in Fiji has found some seaweeds actually produce chemicals that cause coral bleaching and suppresses photosynthesis. This could lead to more discoveries of similar seaweed around the globe, the authors say.

Over the last several decades, scientists have observed numerous coral reefs being overrun by algae but it wasn’t certain if the algae was the cause or if it was just benefiting from the dying reef.

“Now our research suggests that, once corals decline due to a combination of global and local stresses, some seaweeds use chemical warfare to suppress the recovery of remnant adult corals and new coral recruits,” said study co-author Douglas Rasher, a doctoral candidate at the Georgia Institute of Technology in Atlanta.

Just like other algae and seaweed blooms in the lakes and oceans of the world, agricultural and sewage runoff are putting large amounts of nutrients into the water, stimulating the growth.

The study doesn’t seem to think the seaweed has evolved with the chemical makeup to specifically attack coral. “We hypothesize that [seaweeds] may have evolved to produce these compounds on their surfaces in response to competition with microbes or attacks from [grazing animals], which they’ve been fighting for millions of years,” Rasher said.

On top of this, algae-eating animals on the reef, including fish, are in decline. Overfishing is causing a chain reaction in the food chain with a decline in the herbivores that help manage the reef keeping algae and seaweeds in check.

The seaweed-and-coral study is published in the October 17 issue of the Proceedings of the National Academy of Sciences.

Thanks for the tip Niko!

[via National Geographic]


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