"Because researchers did not really begin to study Caribbean reefs in detail until the late 1970s, we don't have a clear understanding of why these reefs have changed so dramatically since this time," said Cramer. "So, we set out to reconstruct an older timeline of change on reefs by looking at the remains of past reefs coral skeletons and mollusk shells."
To reconstruct this timeline, the team dug below modern reefs in incremental layers and, using radiocarbon dating of the coral skeletons they found, linked fluctuations in the types and numbers of coral and mollusks over time to historical records of land clearing. Changes in the relative numbers of these various species represent clear indicators of the overall health of the coral reef.
The team also improved upon the standard technique of taking long, narrow core samples of coral fossils that cannot track fluctuations in the numbers of larger species of coral.
"We wanted to look at the whole complement of the coral community," said Cramer.
To catalog the relative numbers of dozens of coral and molluscan species, the researchers dug two-foot-wide by three-foot-deep pits into reefs at several coastal lagoon and offshore sites near Bocas del Toro, Panama, that were heavily affected and less affected by land runoff, respectively. At each of these sites they also conducted surveys and recorded the composition of living corals.
"We dug up over a ton of coral rubble and tens of thousands of shells," said Cramer, who led the fieldwork at STRI and likened the laborious experience to doing underwater construction.
Systematically sifting through the coral and shell fossils, the scientists noted several indicators of environmental stress, including a decrease in the overall size of bivalves such as oysters, clams
|Contact: Mario Aguilera|
University of California - San Diego