Extreme El Niño cycles seen as cause of coral decline
By Summit Voice
SUMMIT COUNTY — A period of dramatic El Niño-La Niña cycles that started about 4,000 years ago resulted in the near-total collapse of some Pacific coral reef ecosystems, according to a new study that took a close look at long-dead reef skeletons along the Pacific Coast of Panama.
The cross-sections of reef covered the last 6,000 years and showed a “reef shutdown” that lasted about 2,500 years, according to the study, published last week in Science. Similar gaps in coral growth were found as far away as Australia and Japan.
The documented changes could be a warning sign for the modern era of climate change, according to the researchers.
“As humans continue to pump greenhouse gases into the atmosphere, the climate is once again on the threshold of a new regime, with dire consequences for reef ecosystems unless we get control of climate change,” said coauthor Richard Aronson, a biology professor at Florida Institute of Technology.
Doctoral student Lauren Toth and Aronson, her adviser at Florida Tech, led the study of how past episodes of climate change influenced tropical reefs of the eastern Pacific.
“We were shocked to find that 2,500 years of reef growth were missing from the frameworks,” said Toth. “That gap represents the collapse of reef ecosystems for 40 percent of their total history.”
Toth linked the coral-reef collapse to changes in ENSO. ENSO is the climate cycle responsible for the weather conditions every few years known as El Niño and La Niña events.
The timing of the shutdown in reef growth corresponds to a period of wild swings in ENSO. “Coral reefs are resilient ecosystems,” said Toth. “For Pacific reefs to have collapsed for such a long time and over such a large geographic scale, they must have experienced a major climatic disturbance. That disturbance was an intensified ENSO regime.”
Scenarios of climate change for the coming century echo the climate patterns that collapsed reefs in the eastern Pacific 4,000 years ago. The reefs off Panama are on the verge of another collapse.
“Climate change could again destroy coral-reef ecosystems, but this time the root cause would be the human assault on the environment and the collapse could be longer-lasting,” said Aronson. “Local issues like pollution and overfishing are major destructive forces and they need to be stopped, but they are trumped by climate change, which right now is the greatest threat to coral reefs.”
Toth noted more hopefully that reefs have proven resilient in the past, so the potential for recovery should be good if climate change can be mitigated or reversed.
Filed under: biodiversity, climate and weather, coral reefs, El Niño, Environment, La Niña Tagged: | biodiversity, coral reefs, El Niño-Southern Oscillation, ENSO, Florida Institute of Technology, La Niña, oceans, Pacific Ocean