In the early 1980s, staghorn corals in the Caribbean suddenly died off massively--and never recovered. Scientists have been divided over who was to blame: man or the vagaries of nature. Now, cores bored from a Jamaican reef seem to point the finger at man.
The vast staghorn coral forests of Jamaica were a favorite playground for the first scuba-diving reef ecologists in the 1960s and '70s. Nevertheless, they were taken by surprise when their secret garden turned into a field of rubble almost overnight. The same fate struck other reefs of the Caribbean. Since then, scientists have been arguing over the cause for this catastrophe. Some insisted humans were ultimately to blame, noting that the decline came after decades of overharvesting of the fish that normally keep smothering algae at bay. Others pointed to hurricanes and coral diseases at the same time as evidence that such massive die-offs are regular and natural.
To help solve this conundrum, a team led by Richard Aronson of the Dauphin Island Sea Lab in Alabama decided to sample ancient staghorn coral rubble that was deposited over the past centuries. To do this, they pushed 4-meter-long, 7.5-centimeter-wide aluminum pipes into the coral debris on the lagoon bed. "It's not easy pushing them in, and it's a lot worse pulling them out," Aronson says. The cores, which were carbon-dated, gave a continuous record of coral conditions from 1200 years ago until today. Throughout this period, the coral fragments showed only a few marks of scavenging by invertebrates that bore tunnels in dead coral, suggesting that bits of dead coral normally lay on the sea floor only briefly before being buried under fresh coral. Debris from the recent die-off, on the other hand, is riddled with such boreholes, the result of 2 decades of exposure to coral scavengers and no regrowth. This suggests the recent die-off is indeed unprecedented, the researchers report in the April issue of Ecology Letters.
Aronson thinks natural causes may have contributed, but that human disturbance was what set the disaster in motion. "All the stars were aligned in a bad way," he says. Carden Wallace, who studies staghorn corals at the Museum of Tropical Queensland in Townsville, Australia, is "saddened" by the news, but she is happy that research is done to understand the demise of the famous Caribbean staghorn reefs.