Coral at risk of widespread bleaching

Bleached blade fire coral appears on a dive spot known as 45 Foot Reef.
Bleached blade fire coral appears on a dive spot known as 45 Foot Reef. keysinfonet.com

There have been several recent reports about major events of coral bleaching.

Coral reacts to the stress of warmer water by expelling zooxanthellae, the symbiotic photosynthetic algae responsible for nutrient cycling within the coral as well as the coral’s color.

The coral provides algae with a protected environment and the compounds the algae need for photosynthesis (the process by which plants and some other organisms use sunlight to synthesize foods from carbon dioxide and water).

In return, the algae produce oxygen and help the coral remove wastes. Most importantly, zooxanthellae supply the coral with glucose, glycerol and amino acids, which are the products of photosynthesis. The coral uses these products to make proteins, fats and carbohydrates, and to produce calcium carbonate (the white, insoluble solid material that forms hard coral).

Though corals might bleach, they are still alive and able to survive if stressful conditions subside quickly and they are able to regain their algae. Some coral grow new algae and recover from the bleaching. Others die, causing the disappearance of a vital ocean ecosystem.

The dive boat set the anchor recently at a place called 45 Foot reef, and I stepped off the stern. Descending to the reef, I saw several coral looking unnaturally white.

I finned past a brain coral that was completely white. A bit farther down the reef, I spotted what I thought to be fire coral, but the whitish coloration puzzled me.

I snapped a few shots and decided to check with Ken Nedimyer, founder and president of the Coral Restoration Foundation — a Keys-based organization dedicated to creating offshore nurseries and restoration programs for threatened coral species.

Nedimyer confirmed that the image I took was of Blade Fire Coral (Millepora complanata), a species that is especially susceptible to bleaching.

“Last year’s bleaching event killed well over half of the fire coral on the reefs that we surveyed, and some reefs, such as Snapper Ledge, lost almost all of their fire coral,” Nedimyer said.

“Last summer, we spent time looking for unbleached colonies to put in our nursery and on many reefs found only about 1 percent that were not bleached.”

Added Nedimyer: “Of the 16 different genotypes that we found and added to our nursery, 14 did not bleach this summer and the other two partially bleached. We are trying to grow the heat resistant corals in our nursery so that when we put them back on the reef, they stand a chance of surviving the hot summers.”

But Nedimyer is worried about the continued increase in ocean temperatures and disease.

“One of the concerns with these extreme bleaching events is that we’re losing genetic diversity with each event, either from outright thermal stress or from opportunistic disease that is attacking the bleached corals,” he said.

It seems coral bleaching is a worldwide problem.

As reported by Chris Mooney in the Oct. 8, 2015 Washington Post, “For just the third time on record, scientists say they are now watching the unfolding of a massive worldwide coral bleaching event, spanning the globe from Hawaii to the Indian Ocean. And they fear that thanks to warm sea temperatures, the ultimate result could be the loss of more than 12,000 square kilometers, or over 4,500 square miles, of coral this year — with particularly strong impacts in Hawaii and other U.S. tropical regions, and potentially continuing into 2016.”

According to the National Oceanic and Atmospheric Administration, increases in ocean water temperature have also been the culprit in previous coral bleaching events.

Other problems include ocean acidification, which occurs when oceans absorb carbon dioxide from the atmosphere, and increases in sea level caused by melting sea ice and thermal expansion of the oceans making some reefs too deep to receive adequate sunlight

Warmer waters also increase coral diseases such as black band disease, white band disease, white plague and white pox, all of which can lead to mass mortality of coral, and subsequently the entire ecosystem it supports, according to the federation.

According to the Florida Reef Resilience Program, Florida Department of Environmental Protection’s Coral Reef Conservation Program, National Oceanic and Atmospheric Administration, and National Park Service report that Southeast Florida’s coral reefs are succumbing to unprecedented levels of coral disease.

“Florida’s beautiful coral reefs are critical to our tourism and fisheries industries — they provide essential habitat to support a range of biodiversity including many species of fish and invertebrates,” said Meaghan Johnson of The Nature Conservancy.

The glimmer of hope for this year is that there has been a reduction in the temperature of ocean water because of wind and rainfall. This could help coral recover.

The FRRP says boaters and divers can help corals by eliminating contact with the corals. Divers can help diminish the possibility of disease transmission by not diving on another reef after diving on a reef that has diseased coral.

All of us can help by reducing stress on coral from land-based sources of pollution, coastal construction projects and harmful fishing practices.

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