In today’s Academic Minute, Dr. Richard Aronson of the Florida Institute of Technology reveals the connection between coral growth and El Niño.
Richard Aronson is Department Chair and Professor of Biological Sciences at the Florida Institute of Technology in Melbourne, Florida. His research is focused on the reefs of the Eastern Tropical Pacific, where a severe El Niño event in 1982–1983 wiped out vast populations of coral. His work has appeared in numerous peer-reviewed journals and he holds a Ph.D. from Harvard University.
Dr. Richard Aronson – El Niño and Coral Growth
How does climate influence the capacity of corals to build tropical reefs? We wanted to know how important the El Niño-Southern Oscillation, or ENSO, was in driving the ecology of eastern Pacific reefs over their 6000-year history. ENSO is a climatic see-saw in the Pacific Ocean that influences weather conditions around the world. ENSO consists of a hot El Niño phase and a cold La Niña phase, both of which suppress the growth of corals in the tropical eastern Pacific.
The prevailing model is that reefs are poorly developed in the eastern Pacific because El Niño events kill the corals every ten to twenty years. The corals recover, only to be knocked back again, and the result is slow reef growth.
We reconstructed the history of reefs in Pacific Panama by taking cores through reef frameworks and analyzing and dating the corals we collected. We discovered that coral populations grew rapidly from 6000 years ago until 4100 years ago, but then they stopped growing for the next 2500 years. They started up again around 1600 years ago. Other researchers have reported gaps in coral growth at the same time on reefs in Costa Rica, Australia, and Japan.
The likeliest reason coral populations collapsed 4100 years ago was an increase in the variability of ENSO, meaning that both El Niño and La Niña events became more frequent and extreme. Both types of events are detrimental to corals, and a continuous barrage of extreme conditions would have suppressed reefs for a long time. Coral populations recovered when some components of ENSO began to ease up 1600 years ago.
Our research shows that reefs in the eastern Pacific are poorly developed, but that’s not because coral growth was suppressed for short periods by El Niño events over their entire history. They are poorly developed because coral populations collapsed from extreme ENSO swings for a 2500-year interval spanning 40% of their history.
A return to extreme, El Niño-like conditions in a warming climate could portend another shutdown of eastern Pacific reefs.