The bleaching and death of corals is causing far-reaching changes in the world's marine ecosystems, including how small fish are able to detect and avoid potential predators, a new study says.

Researchers from James Cook University (JCU) in Australia and Uppsala University in Sweden examined how certain changes in coral reef systems impact the lives of the thousands of aquatic animals that depend on them.

In a study featured in the journal Proceedings of the Royal Society B, the team described how the death and continued degradation of many of these coral reef systems is altering the common damselfish's ability to detect the presence of prospective predators.

Mark McCormick, an expert on coral reef fish at JCU and one of the authors of the study, explained that juvenile fish typically use chemicals released from the skin of attacked animals as a form of early warning system to let them know if there are predators nearby. They then combine these chemical cues with the sight or smell of other creatures to determine whether they should avoid them in the future.

However, the death of corals is severely affecting the ability of fish to detect danger through chemicals in the water. As corals die, their bodies become covered in algae that release chemicals themselves, causing fish to get confused by the signals.

During one observation, the researchers discovered that the smell of an attacked ambon damselfish helped others become aware of predators in their surroundings and they developed ways on how to avoid these dangers.

Fish that were placed near dead corals, however, failed to detect predators in their midst and were not able to create strategies to avoid them.

The team also found one species that was able to detect potential predators using the same chemical alarm system regardless of whether it was living near live or dead corals.

Marine Biologist Oona Lönnstedt said that if the process of how these animals detect and avoid predators is hindered by coral loss and degradation, it could produce widespread repercussions on the diversity of reef fish as well.

The researchers pointed to the massive coral bleaching that the Great Barrier Reef is experiencing right now as a particular concern. They said that the majority of the coral cover on the system is declining significantly.

"If dead coral masks key chemical signals used to learn new predators, the replenishment of reefs could be seriously threatened", Lönnstedt said.

Photo: Jorge Láscar | Flickr

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