As a STRI short-term fellow, Catie Kuempel joined staff scientist Andrew Altieri to explore a large area of the sea floor in Bocas del Toro, Panama, where corals had died but, surprisingly, algae had not taken over. The most common algal grazers they found were a small sea urchin about the size of a ping pong ball, Echinometra viridis, and a tiny finger-sized striped parrot fish, Scarus iseri, which would be of no interest to fishermen.
In Jan., 1983, STRI staff scientist Harilaos Lessios noticed that long-spined black urchins, but not other species of urchins were dying near the Atlantic entrance of the Panama Canal. He contacted dive shops and was able to track the mass mortality of urchins as it spread across the Caribbean from 1983-1984.
Subsequently deprived of this large species of grazer, algae grew unchecked, especially on reefs where overfishing had eliminated large parrotfish. Today, despite the fact that Diadema antillarum has recovered in some areas, the total number of this urchin in the Caribbean is still only about 12 percent of pre-die-off numbers.
Catie Kuempel and Andrew Altieri at the Smithsonian Tropical Research Institute’s Bocas del Toro Research Station, caged corals to find out how much algae grows on them in the absence of grazing organisms. They found that even small grazers can do the job of controlling algal growth on coral colonies.
Credit: Andrew Altieri
“Given that the frequency of coral disease will probably increase with global warming and that overfishing can be prevented only in protected areas, which cannot expand indefinitely if people continue obtaining their protein from the sea, the best hope for Caribbean reefs is that D. antillarum will recover,” Lessios predicted.
Based on their observations in Bocas del Toro, Kuempel and Altieri are more hopeful, suggesting that management and monitoring strategies aimed at preventing phase-shifts from coral to algae on reefs should broaden to include the role and importance of diminutive species of herbivores. “These dollhouse-sized species came the rescue of reefs in Panama, and may be important elsewhere as well,” said Altieri.
They will continue to explore whether the algae consumption by these small species that tips the balance back from algal domination of dead reefs is clearing the way for new coral growth.
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