Researchers from the Scripps Institute of Oceanography (University of California San Diego) have discovered that coral reefs grow faster when there are more algae-eating fish around.
They arrived at this conclusion after analysing fossilised parrotfish teeth and sea urchin spines from the past 3,000 years at the reefs off Panama, in a bid to uncover the cause of the present-day shift from coral- to algae dominated reefs that is taking place across the Caribbean.
“Our reconstruction of past and present reefs from fossils demonstrates that when overfishing wipes out parrotfish, reef health declines,” said Katie Cramer, a postdoctoral researcher at Scripps. She is also the lead author of a paper about the discovery, published in the latest issue of Nature Communications journal.
In the coral reef ecosystem, parrotfish (and other herbivorous fish) are essential as they consume the algae that compete with corals. Over the last several decades, the reefs in the Carribbean became more dominated by algae, a situation that was mainly caused by the decline in the number of herbivorous fish like the parrotfish, according to the study.
For the study, sediment cores from three reef sites offshore of Bocas del Toro, Panama were examined to assess the original state of the reefs before intensive fishing and land clearing took place. The researchers also wanted to find out the role of such activities in the recent reef declines. The purpose was to determine whether the growth rate of the corals was affected by changes in the population sizes of both the parrotfish and sea urchins.
The researchers then concluded that the presence of parrotfish at the reefs was good news for coral growth; on the other hand, the presence of sea urchins did not have any effect.
“Using the fossil record to analyse the natural state of reefs before human disturbance, we have conclusively shown that if we want to protect corals we have to protect the parrotfish from overfishing,” said Cramer.