Katie Cramer collects coral skeletons and shells in Panama. (Photo: Scripps /ucsd.edu)
Caribbean coral reef decline started a century ago: study
Monday, April 02, 2012, 22:30 (GMT + 9)
The decline of Caribbean coral reefs has been linked to the recent effects of human-induced climate change. However, new research led by scientists at Scripps Institution of Oceanography at UC San Diego suggests an even earlier cause.
The bad news – humans are still to blame. The good news – relatively simple policy changes can hinder further coral reef decline.
Employing a novel excavation technique to reconstruct the timeline of historical change in coral reefs located on the Caribbean side of Panama, a team of scientists led by Scripps alumna Katie Cramer and current Scripps Professor of Oceanography and Smithsonian Tropical Research Institute (STRI) Emeritus Staff Scientist Jeremy Jackson has determined that damage to coral reefs from land clearing and overfishing pre-dates damage caused by anthropogenic climate change by at least decades.
"This study is the first to quantitatively show that the cumulative effects of deforestation and possibly overfishing were degrading Caribbean coral and molluscan communities long before climate change impacts began to really devastate reefs," said lead author Cramer, currently based at the Global Coral Reef Monitoring Network at the International Union for Conservation of Nature (IUCN).
|Staghorn corals in Caribbean. (Photo: explorations.ucsd.edu)
Historical records and qualitative surveys provide hints that declines in corals in some parts of the Caribbean occurred as far back as the early 1900s after coastal lands began to be cleared to make way for plantations.
The current study is the first to quantify the changes that reef corals and molluscs have undergone as a result of long-term stress caused by the deposition of silt, nutrients, and pollution onto coral reefs from land clearing and the depletion of reef fish that prevent algae from overtaking reefs.
"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 mollusc 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 molluscs 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 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.
The scientists noted several indicators of environmental stress, including a decrease in the overall size of bivalves such as oysters, clams, and scallops, a transition from branching to non-branching species of coral, and large declines in the staghorn coral and the tree oyster, which were once the dominant coral and bivalve on these reefs.
With the decline of the branching coral species, the reefs now have fewer nooks and crannies that are used as habitat for reef fish and other organisms. Also, the non-branching species that have taken their place grow at a much slower rate.
"Consequently, there is less of a chance that the reefs will be able to keep up with sea level rise from climate change," said Cramer.