New research published in Nature Communications highlights the importance of parrotfish to the healthy growth of Caribbean coral reefs.
Coral reefs are crucially important habitats for many marine species but they are currently undergoing a worldwide conservation crisis. In 2014, the Global Coral Reef Monitoring Network of the IUCN released a report showing that Caribbean coral reefs have declined by more than 50% since the 1970s. The report stated that a major cause of this decline was likely to be the overfishing of parrotfish in addition to other factors such as climate change and pollution.
Parrotfish play an important role in coral reef ecosystems by feeding on algae, and it is thought that declines in their numbers may be a major factor in the spread of increasingly algae-dominated reefs throughout the Caribbean.
Slices of Reef History
In order to investigate the historical relationship between the Caribbean coral reefs and their parrotfish, a team of researchers from Scripps University extracted core samples from the reefs surrounding Panama’s Bocas Del Toro archipelago. The 3-4m long core samples contained fossilised parrotfish teeth and sea urchins that were counted to create a 3,000-piece picture of the reef’s biological history.
Using dynamic modelling techniques, the researchers showed that corals thrived with an abundance of parrotfish but were not affected by the abundance of sea urchins that also feed on algae. It appeared that the beneficial effect to coral of parrotfish herbivory on algae seemed to outweigh any harm caused by parrotfish directly consuming the coral itself, and yet for sea urchins, the benefit of their herbivory was counteracted by the detriment of sea urchins’ intensive coral boring. Therefore when it comes to maintaining the health of a coral reef, the scientists concluded that parrotfish are much more important herbivores than sea urchins.
The analysis also highlighted the grim effect of relatively recent human activity on the parrotfish populations. In past centuries, changes in the hydrology of the region appeared to have been the main reason for coral reef declines, not necessarily the actions of humans—yet in the last two hundred years or so the analysis clearly implicated the overfishing of herbivorous fish by humans in the decline of coral reefs.
“These findings reveal that parrotfish indeed have a positive and critical role in coral health, a hotly debated issue in coral reef research that cannot be resolved with studies of modern reefs which have already been greatly altered by human activities,” said Katie Cramer, a postdoctoral researcher at Scripps and lead author of the study. “Using the fossil record to analyze 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.”
The 2014 IUCN report recommends legally protecting parrotfish from fisheries, strictly enforcing fishing restrictions and educating the public on the ecological importance and economic benefits of wild parrotfish. Hopefully, we can look forward to a turn-around for the parrotfish of the Caribbean and the opportunity for our currently fragile corals to flourish.
“These results confirm the critical role of parrotfish in maintaining coral-dominated reef habitat and the urgent need for restoration of parrotfish populations to enable reef persistence,” concluded the authors.
Katie L. Cramer, Aaron O’Dea, Tara R. Clark, Jian-xin Zhao, Richard D. Norris. Prehistorical and historical declines in Caribbean coral reef accretion rates driven by loss of parrotfish. Nature Communications, 2017; 8: 14160 DOI: 10.1038/ncomms14160
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