Mote Marine Laboratory

Coral Reef Comeback?

By: Kasey Williams

A long-spined sea urchin could be one key to coral survival

Diadema antillarum is a long-spined sea urchin that was highly abundant in the Caribbean region until a widespread disease of unknown origin killed 97 percent of the population between 1983 and 1984. Diadema abundance has remained extremely low ever since.

Diadema are extremely important to the Caribbean coral reefs because they are the main regulators of macro algae. Unchecked, macro algae can overgrow and kill corals, which is what has happened in many locations. Diadema can also influence the success of coral larvae that settle on the reef, thus affecting new generations of coral.

In “Diadema antillarum 17 years after mass mortality: Is recovery beginning on St. Croix?” published in the journal Coral Reefs, 2003, Dr. Aaron Adams, program manager for fisheries habitat in Mote’s Center for Fisheries Enhancement, and colleagues John Ebersole and Robert Miller from the University of Massachusetts Boston, looked at the number of urchins living on coral reefs in St. Croix, U.S. Virgin Islands.

Scuba divers counted the number of urchins four times at eight locations and discovered a possible population resurgence. In recent years, the population has grown more than 100 percent on the back reefs and more than 350 percent on the patch reefs compared to the numbers seen in the mid-1990s. If this recovery continues and Diadema once again act as a control for macro algae, a return to coral-dominated reefs could occur.

New Diadema research includes additional sampling to see whether the possible recovery is continuing.

Adams and colleagues are also studying whether juveniles are more or less likely to survive in areas where adults are living, whether coral growth is greater and macro algae growth is lower in areas with more Diadema, and whether Diadema has a negative influence on the abundance of algae-eating fish species.

Learn more about: Coral Reef Research

Are you just urchin to help? All components of marine reef communities could use our help. And we could use yours. Now. So dig deep and don't hold back.