Bleaching Threatens Caribbean Coral; Experts Say Reefs in Critical Condition

Coral affected by the current bleaching episode, above, appear white or pale.

Although it might go unnoticed by the average observer, there is a serious problem lurking under the calm surface of the Caribbean waters and, if it continues, the future of our underwater resources and above-water economy will be in jeopardy.

A “full-on bleaching episode” is taking place throughout the Caribbean due to elevated water temperatures which have caused the normally healthy, earth-toned coral to turn pale or even white, according to local marine experts. “We are seeing a full on bleaching episode right now throughout the Caribbean,” said Jeff Miller, fisheries biologist for the National Park Service.

“It is shocking – this is a very alarming situation,” said Dr. Caroline Rogers, U.S. Geologi-cal Survey marine ecologist. “People are coming up to me on the street saying they just went diving and all of the coral they are seeing has turned white.”

Elevated Temperatures
Bleaching of coral reefs can occur when the sea water temperature is elevated and there are high light levels, causing the microscopic plants within the coral to be expelled or lose pigment, resulting in corals that appear pale or white, explained Miller.

Critical Condition
The bleached coral reefs are still alive but are in “critical condition” and could die. “They are still alive – but nobody can say whether they will survive this bleaching episode that is happening right now,” said Dr. Rogers. “We have seen an increase in just in the last seven days – it has gotten worse.” The bleaching episode in local waters began in August and is ongoing, bleaching healthy coral at a very rapid pace, according to marine experts.

The bleaching of coral, solar-powered animals, can be compared to a person who is ill, according to the experts. “When someone is sick, they can look pale and that is not all that different from what we are seeing now with this mass bleaching episode,” said Miller. “And the hard reality is that the corals could all die – this could be catastrophic if the corals do not recover.”

Corals need an extra energy source to grow into the reefs we see today, which take thousands of years to develop, according to Miller. The most common coral on St. John, “star coral,” grows at a rate of the thickness of a dime each year, he added. “Corals cannot get enough food from what they eat – they get the extra energy from the plant cells that live in their tissue, and coincidentally, those plant cells give the corals their color,” said Miller.


Coral displays normal earth-toned coloration.

Colors from Plant Cells
The colors of the corals are a reflection of the pigmentation of the plant cells that live in their tissue, he added. Healthy corals are earthtone colors, mainly brownish or greenish, derived from amount of plant cells in their tissue, but a variety of situations such as unclear water, salinity content nutrients or extreme sunlight can cause coral to become stressed.nutrients or extreme sunlight can cause coral to become stressed.

“When any of these things are out of whack, corals become stressed, and one of the primary ways stress affects the coral is by causing the coral to expel their plant cells,” said Miller. The bleaching episode occurring right now is caused by the elevated water temperatures, which are significantly warmer than the coral can tolerate, he reiterated.

“These reefs are being severely threatened right now by the elevated sea water temperatures,” said Miller. This Septem-ber, typically the warmest month of the year when the most bleaching would occur, had the warmest average temperature since monitoring began 15 year ago, he added. “The white reef we are seeing now is severely stressed; the coral has lost significant source of energy,” said Miller. “In hospital terms, it would be considered in critical condition.” When corals are bleached, they are more susceptible to coral diseases, which is an added risk factor, pointed out Miller. “And we are seeing more corals and species of coral affected,” he added.

Life Without Coral Reefs
Putting a dollar value on coral reefs is challenging, but one report estimates an annual net economic value in 2000 for Caribbean coral reefs is between $3.1 and $4.6 billion from fisheries, dive tourism and shoreline protection alone, according to Miller. Coral reefs provide shelter and habitat for reef fish, other sea life and serve as a breakwater for shorelines, according to the marine experts.

If the coral reefs we see today, which take thousands of years to develop, die, there will be severe repercussions – sea life will die, tourism will decline and the reefs, which protect shorelines by serving as natural breakwaters for huge waves will no longer be there, resulting in tremendous eroding or loss of beaches entirely. The importance of coral reefs was demonstrated during the tsunami of 2004, according to the biologist.

Where coral reefs existed in healthy condition, the waves from the tsunami were weakened, resulting in less damage and loss of life in coastal areas where reefs were healthy whereas areas where reefs were destroyed had nothing to weaken the waves, according to Miller.

“That is what coral reefs do – provide natural protection for the shorelines, and if the coral reefs are lost, we lose our natural barrier against wave action and our shorelines are at risk,” said Dr. Rogers.

Similar Bleaching in 1998
Field experts observed a previous bleaching episode throughout the Carib-bean in 1998 when similar environmental conditions prevailed, characterized by warm water temperatures and calm seas, which allow more light to penetrate the coral, according to the marine ecologist. “This is alarming – we haven’t seen anything like this since 1998 and we don’t know if the coral will recover,” said Dr. Rogers.

Recovery Time Unknown
In 1998, the waters cooled down and the corals did recover, but experts are not sure what will happen in this case. “We don’t know how long it will take for these corals to recover – if they do recover like they did after the 1998 bleaching episode, in which the corals sustained low levels of mortality,” said Miller. “Hope-fully this will be the case again, but at this time we can’t say.”

Many consecutive cloudy days, a surplus of rainfall, even a hurricane or any weather pattern which brings in cooler waters will reduce the impact of this bleaching, according to Dr. Rogers. “It took a while for this bleaching episode to occur and it will take a while for it to go away,” said Miller.