Fun with Science Club®


			Can sea urchins kick out the algae and bring in the coral? Carrie Straight 05.18.01 Different habitats throughout the world go through continual changes. One of these changing habitats is a coral reef. Coral reefs are changing from coral dominant to a macroalgae dominant, these are larger species of algae. Scientists believed it would be difficult, maybe even impossible, for a macroalgae-dominated reef to change back to a coral based reef. Traditionally the coral reefs have many sea urchins, Diadema antillarum. Reefs taken over by macroalgae don’t have sea urchins. Some scientists wanted to find out more about the relationship between the sea urchins, coral, and the macroalgae. During their research, this group of scientists found a reef that appeared to be changing back to a coral based reef. They predicted that in areas of reef where sea urchin populations recovered the coral would also recover and increase in number. They tested this prediction by choosing reef sites along the coast of Jamaica. At these sites, they made systematic observations. They counted the number of sea urchins and juvenile (young) coral at each site and measured their sizes. They measured the area covered by macroalgae, other algae, and live coral. The scientists discovered that when the number of sea urchins in an area increased the percent of the area covered by macroalgae decreased and the number of juvenile corals increased. The sea urchins can change a macroalgae dominant reef back to a coral dominant reef.


			Edmunds, Peter J. and Robert C. Carpenter. 2001. Recovery of Diadema antillarum reduced macroalgal cover and increases abundance of juvenile corals on a Caribbean reef. Proceedings of the National Academy of Sciences 98(9): 5067-5071.