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Aggressive, territorial fish can help boost coral reef recovery

Coral reefs around the world have been experiencing mass bleaching events and are dying off at an unprecedented rate. Famously, the Great Barrier Reef experienced catastrophic back to back bleaching events in 2016 and 2017.

Scientists are now working to predict how the world’s corals will respond to warming ocean temperatures caused by climate change.

While the future doesn’t look promising, research has shown that corals can adapt to environmental changes and recover.  But can corals keep up with the fast pace of climate change? And what intervening methods can conservationist employ to help corals recover?

Researchers from the University of California-Santa Barbara and Rice University conducted a new study examining the relationship between rising temperatures, fish aggression, and coral recovery to see how fish impact coral growth.

The results, published in the journal Behavioral Ecology, show that an increase in water temperatures may benefit corals to some extent because it increases the aggressiveness of some species of fish that guard the reef.

“Predicting the future of corals will require a systems approach,” said Jonathan Pruitt, the lead author of the study. “Failing to account for broader ecological processes, such as species interactions, could lead us to issue the wrong predictions about how some corals will fare in future environments.”

For the study, the researchers focused on farmerfish (stegastes nigricans), which are an aggressive species of damselfish that live around coral reefs in tropical climates. The fish guard gardens of algae which is how they get their name and the researchers wanted to see how farmerfish aggression impacted coral performance.

The researchers planted coral fragments into 29 farmerfish colonies with different levels of aggressiveness in French Polynesia and observed the colonies for a year between 2016 and 2017.

Aggressiveness was evaluated along with fish size and a group’s reaction to an intruder. The researchers also measured coral growth and recovery.

At the end of the study, the researchers found that aggressiveness correlated with an increase in branching corals near the farmerfish colonies. Corals that were planted in non-aggressive farmerfish territories showed 80 percent more damage compared to corals in aggressive colonies.

While larger sized farmerfish had more aggression, the researchers found that group aggression was more important than size in determining coral performance.

The researchers say that because warmer waters can increase fish aggression, coral recovery may have more of a chance than previously thought in a warming world.

“Heating up many corals even mildly can negatively impact a variety of physiological processes,” said Pruitt “However, this study shows that small increases could provide greater protection by resident fishes. Obviously, this can’t go on for forever, though. At some point, all the protection in the world won’t matter anything if the corals can’t feed themselves”

By Kay Vandette, Staff Writer

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