Summit County Citizens Voice

Coral reef biodiversity likely to take a big climate change hit.

Free-floating coral likely to survive; structured reefs will probably disappear

By Summit Voice

SUMMIT COUNTY — Fossilized coral reefs more than 2 million years old are providing some clues about how global warming may affect existing reefs.

Scientists from the University of Miami are analyzing reefs from Pliocene era, when carbon dioxide levels and mean global temperatures were similar to conditions expected in the next 100 years.

“If the coming century truly is a return to the Pliocene conditions, corals will likely survive, while well-developed reefs may not,” said University of Miami geology professor James Klaus. “This could be detrimental to the fish and marine species that rely on the reef structure for their habitat.”

The study looked at the fossil records of coral communities from nine countries around the Caribbean region to better understand the nature of these ecosystems during the Pliocene. The fossil reefs are often found far from the sea, exposed in road cuts, quarry excavations, or river canyons due to uplift and higher ancient sea levels.

The study found a striking difference between modern and Pliocene coral communities. The Pliocene epoch was characterized by a great diversity of free-living corals. Unlike most reef corals, these corals lived unattached to the sea floor. Free-living corals were well suited to warm, nutrient-rich seas of the Pliocene. Between eight and four million years ago the origination of new free-living coral species approximately doubled that of other corals.

However, free-living corals experienced abrupt extinction as seawater cooled, nutrient levels decreased, and suitable habitat was eliminated in the Caribbean. Of the 26 species of free-living corals that existed during the Pliocene, only two remain in the Caribbean today. The modern Caribbean coral fauna is comprised of those coral species that survived this extinction event.

The scientists argue that the effects of ongoing climate change are reminiscent of conditions present during the Pliocene and opposite to the environmental factors that caused the extinction and gave rise to modern Caribbean corals. So, how might the Caribbean coral fauna respond to a predicted return to Pliocene–like conditions within this century?

The free-living corals of the Pliocene would have been well suited to ocean conditions projected for this century. However, the modern reef-building coral fauna may not, explains Donald McNeill, senior scientist in the Division of Marine Geology and Geophysics at UM and co-author of the study.

“Like the Pliocene, we might expect shallow reefs to be increasingly patchy with lower topographic relief,” says McNeill. “Rising levels of carbon dioxide will lower the pH in the oceans, a process known as ocean acidification, and will make it difficult for corals to build their limestone skeletons.”

Climate change may also increase nutrients in the oceans, boosting populations of marine life that degrade the coral into fine white sand, a process called bioerosion. Reefs built by corals in areas with high bioerosion will be affected the most. Mesophotic reefs, those growing in depths between 30 and 150 meters, have reduced rates of both calcification and bioerosion and thus may be affected less.

Related Articles

• Ten years to save Australia’s Great Barrier Reef (newscientist.com)
• Extinction predictor to help protect coral reefs (sciencedaily.com)
• Why Australia’s Great Barrier Reef Needs Saving (time.com)

Filed under: biodiversity, climate and weather, coral reefs, global warming Tagged: | Caribbean, climate change, coral reefs, Environment, global warming, Pliocene, Summit County News, University of Miami