Warming sea threatens Caribbean corals

Posted: 7 June 2007

Caribbean coral species are dying off, indicating dramatic shifts in the ecological balance under the sea, a new scientific study of Caribbean marine life shows.

Healthy coral reef
Healthy coral reef
A healthy reef on Bonaire, Netherlands Antilles, retains the three-dimensional structure that was once typical of coral reefs across the Caribbean and that provided shelter to a vast diversity of Caribbean fishes and other species. The coral species that are dominant in this view - staghorn coral (Acropora cervicornis) and elkhorn coral (Acropora palmata) - are both critically endangered. Photo © Andy Bruckner/NOAA Fisheries
The study found that 10 per cent of the Caribbean's 62 reef-building corals were under threat, including staghorn and elkhorn corals. These used to be the most prominent species but are now candidates to be listed as Critically Endangered on the IUCN Red List of Threatened Species.

"One of the Atlantic Ocean's most beautiful marine habitats no longer exists in many places because of dramatic increases in coral diseases, mostly caused by climate change and warmer waters," said Dr. Michael L. Smith, director of the Caribbean Biodiversity Initiative at Conservation International.

Diseased brain coral
Diseased brain coral
Two colonies of brain coral (Diploria strigosa) on Curaçao show the effects of white plague coral disease. The colony on the left has died completely, and the disease has spread to the colony on the right, where it shows as a stark white band encroaching on the still-living, colourful part of the colony. Photo © Andy Bruckner/NOAA Fisheries
A gathering of 23 scientists in Dominica in March 2007 analysed data on Western Tropical Atlantic corals, seagrasses, mangroves and algae, which are fundamental components of marine ecosystems providing food and shelter for numerous other organisms and local communities. The study was funded in part by the Royal Caribbean Cruises' Ocean Fund.

This was the first in a series of Global Marine Species Assessments (GMSA) of key marine primary-producers on a global scale. The GMSA is headquartered at Old Dominion University in Norfolk, Virginia, and is a partnership between Conservation International (CI) and the World Conservation Union (IUCN). It aims to dramatically increase the number of marine species assessed under the rigorous criteria of the IUCN Red List of Threatened Species to provide up-to-date information for marine policy and conservation efforts.

Coastal pollution

After a final review, the species assessed during the Dominica workshop will be added to the 2008 IUCN Red List.

Diseased star coral
Diseased star coral
A colony of mountainous star coral (Montastrea faveolata) with black band disease. This colony is about 300 years old and lost about one-third of its tissue in a few weeks. The ruler is 154 cm (six inches). Photo © Andy Bruckner/NOAA Fisheries
"Coral reefs support some of the richest areas of biodiversity in the world. When the coral reefs disappear, so will many other species which rely on reefs for shelter, reproduction and foraging," said Dr. Suzanne Livingstone, GMSA programme officer.

The threats to corals and other marine species include coastal pollution and human development; increased sedimentation in run-off water; thermal stress and heightened severity of hurricanes from climate change; and shifts in species dynamics due to over-fishing, according to the study. Scientists explained that the Caribbean has undergone the longest and most sustained impacts from human development since the colonization of the Americas.

Next to corals, mangroves appear to be the hardest hit. Mangrove cover in the region has declined by 42 per cent over the past 25 years, with two of the eight mangrove species now considered Vulnerable to extinction and two more in Near Threatened status.

"Mangroves protect shorelines, shelter fish, and filter pollution," said Aaron Ellison of Harvard University. "The Caribbean was blessed with an abundance of these useful plants, but the consensus of this workshop is that mangroves are in trouble everywhere and need to be protected and restored," he added. Mangrove forests are being cut down to make way for coastal housing, tourism, and aquaculture development.

Beds of sea-grasses in shallow coastal waters, like mangroves, provide a vital nursery habitat for fish, including many commercially important species and are subject to similar threats. They are in equal need of protection to safeguard the wealth of marine life they support.

Unlike corals, seagrasses and mangroves, Caribbean algae appear to be surviving well and perhaps are taking advantage of the corals' demise. Algae thrive on dead or dying coral reefs and can overgrow and smother newly settled corals. In addition, the fishes that feed on algae are being overexploited and their reduced populations enable algae to form dense growths that prevent corals from re-colonising.

The scientists noted that some healthy Caribbean coral reefs still exist in well-managed marine protected areas such as Bonaire Marine Park in the Netherlands Antilles. Direct human impacts are reduced in these areas allowing most corals to thrive; however, thermal stress from global warming affects all corals in the Caribbean and must be reversed if these refuges of Caribbean beauty are to survive, they added.

"The Caribbean tourism industry relies heavily on the beauty and health of its sea life," said Dr. Kent Carpenter, GMSA Director. "Concentrated marine conservation and a global effort to halt man-induced climate change are necessary to preserve this vital economic engine in the region."

Related links:

Human activities threaten Caribbean coral reefs

Coral atlas maps world's fast disappearing coral reefs

Caribbean atoll reveals unique marine treasures