Coral reefs grow faster and healthier when Parrotfish are abundant…

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In a recent study from Smithsonian scientists in the Bocas del Toro archipelago of Panama, fossils, sediments, and core samples were analyzed to determine coral growth rates (accretion) with parrotfish abundance over a time frame of 3,000 years. The team took six 33 ft core samples and dated fossils using uranium-thorium isotope analyses, which can provide extremely fine-scale resolution down to just a few years. Samples dated back to 997 B.C. and exhibited a range of conditions before pollution and wide-spread disease outbreaks, as well as die-offs of the long-spined sea urchin (Diadema) which grazes on algae and helps prevent coral from becoming smothered.

“This fossil record of reefs provides evidence that parrotfishes were actually causing faster reef growth, rather than the other way round, or the two simply being driven by a third factor,” said Aaron O’Dea, a co-author of the study and scientist at the Smithsonian Tropical Research Institute in Panama. “Because of this intimate causal relationship between parrotfishes and healthier reefs, we support the call that parrotfish conservation be made a priority for the recovery and persistence of Caribbean coral reefs.”

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The authors used an empirical dynamic mixed model to assess the cause-and-effect relationships among different members of the coral reef community. The focus on parrotfish is a vital key to conservation approaches, as they play a large role in shaping coral reef ecosystems. In many coastal and island nations however, parrotfish are prized catches for food and many modern reefs are showing declines in parrotfish abundance (Source).

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“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 Cramer, who conducted the Panama portion of the research while a Smithsonian MarineGEO post-doctoral fellow. “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 parrotfish from overfishing.”

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There are many efforts to help conserve parrotfish in tropical areas where over-fishing has devastated their abundance; size and gear restrictions are one way in which fishing pressure can be relieved, given proper management.