Declines in Caribbean coral reefs pre-date damage resulting from climate change

Mar 30, 2012
Tree oyster Dendrostrea frons attached to staghorn coral Acropora cervicornis. Credit: Jill Leonard-Pingel

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 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.

Coral reefs have suffered alarmingly since the 1980s due to coral bleaching and coral disease, thought to stem from the warming of the oceans due to anthropogenic, or human-induced, climate change. However, until recently, the impact of prior human activities on had not been studied with experimental techniques.

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. However, the current study is the first to quantify the changes that reef corals and mollusks have undergone as a result of long-term stress caused by the deposition of silt, nutrients, and pollution onto 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 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, 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.

These indicators were observed in layers of the excavated pits at coastal lagoon sites that were dated before 1960 and as far back as the 1800s, corresponding to a period of extensive deforestation in the Bocas del Toro region. Similar evidence of environmental stress at offshore sites was dated after 1960, indicating that the negative impacts of land clearing have more recently begun to affect reefs further offshore.

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.

"Because the governments of the world have yet to undertake any meaningful efforts to mitigate , it is of the utmost importance that locally caused stressors to reefs such as overfishing and deforestation are minimized," said Cramer. "Advocating for more intelligent use of land as well as implementing sustainable fisheries management, those are things that can be done right now."

Explore further: Green dream: Can UN summit revive climate issue?

More information: The research team will publish its findings in the April issue of Ecology Letters. An early online version has been released today.

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NotParker
3.4 / 5 (5) Mar 30, 2012
While I think it is courageous to not blame global warming from some damage to one of the key "poster boys" of AGW hysteria, it is quite cowardly to claim AGW is causing problems.

Coral has survived the oceans rising 100s of meters since the end of the last ice age. And coral has survived the Little Ice Age and other warming periods like the MWP.

gromm1t2
2.6 / 5 (5) Mar 30, 2012
And, with just a little bit of luck, enough corals will survive to repopulate the earth after we've despoiled it so severely that we humans can no longer tolerate living in our own filth.
mcausal
3 / 5 (6) Mar 30, 2012
While I think it is courageous to not blame global warming from some damage to one of the key "poster boys" of AGW hysteria, it is quite cowardly to claim AGW is causing problems.

Coral has survived the oceans rising 100s of meters since the end of the last ice age. And coral has survived the Little Ice Age and other warming periods like the MWP.



did you read the article??

also, if we blow out all gas and oilfields on the planet, set them on fire and dance to the flames, something will still survive.... great news i guess?
Callippo
1 / 5 (4) Mar 30, 2012
Coral reefs aren't the only organisms, which are facing fast decline: for example the frogs have the same problem. So I don't think, the frogs suffer with overfishing, these two extinctions are apparently related by climate change: the warm and dry climate just changes the equilibrium between prey and predators, various parasitic diseases in particular.
Sanescience
5 / 5 (3) Mar 30, 2012
Humans have an amazing ability to decide on a topic and use filters and evaluations to reinforce those positions they hold. Research in this area is well documented and unfortunately awareness of this propensity does not seem to mitigate it.
NotParker
1 / 5 (2) Mar 31, 2012
did you read the article??


Yes.

"These indicators were observed in layers of the excavated pits at coastal lagoon sites that were dated before 1960 and as far back as the 1800s"

Any problems the coral are having has NOTHING to do with CO2.
NotParker
1 / 5 (1) Mar 31, 2012
also, if we blow out all gas and oilfields on the planet, set them on fire and dance to the flames


Iraq did that to Kuwait.

Can you point to any lasting or noticeable damage?
Maliseil
1 / 5 (2) Apr 05, 2012