| |
 |
The once thriving Andros Reef is now threatened. In the past, antler-shaped elkhorn coral dominated the reef, with multiple colonies extending continuously for long stretches. Throughout the Caribbean today, this species exists primarily in isolated colonies-and scientists estimate that in certain places, up to 95 percent of elkhorn coral has died. © G. Carleton Ray / Photo Researchers |
In the shallow waters off the coast of Andros Island in the Caribbean, corals of all shapes and sizes form the Andros Reef, one of the largest barrier reefs in the world. Like other coral reefs, Andros was created by massive colonies of coral polyps, which are small, soft-bodied animals. These creatures have hard skeletons that form much of the structure of a coral reef.
A variety of coral species make up the Andros Reef, including antler-shaped elkhorn coral, round brain corals and wispy sea fans. Within an individual species, there can be considerable diversity in shape and color, making the reef a maze of colorful caves and crevices. These openings in the reef are home to numerous species of fishes as well as other organisms.
This diorama depicts the Andros Reef as it was in the 1930s. Today, however, Andros and most other reefs around the world are threatened or endangered; many reefs are already dead or severely damaged.
Although numerous fishes and other aquatic species still seek shelter in the Andros Reef, many of the corals themselves are no longer alive—only their limestone skeletons remain. Many forces contribute to the destruction of coral reefs around the globe. Pollutants in runoff from nearby land can weaken or kill coral reefs. Overharvesting of fish that graze on patches of algae occurring naturally on reefs allows the algae to grow unchecked, blanketing the coral underneath.
Rising water temperatures, caused in part by global warming, pose another serious threat to reefs. The small coral polyps, the animals that build reefs, obtain much of their food from tiny dinoflagellate algae living inside their tissues. These symbiotic algae also give the reefs much of their color. A small increase in water temperature disrupts the algae, causing them to leave the coral tissues. Without these beneficial algae, corals sometimes turn ghostly white and die, a phenomenon known as "coral bleaching."
 
|
