Coral Bleaching Triggers Increased Fighting Among Fish, Threatening Survival

A new study published in the journal Proceedings of the Royal Society B has found that mass coral bleaching is causing increased fighting among fish, potentially threatening their survival. The research team studied the impact of a mass bleaching event on 38 species of butterflyfish, which are the first to feel the effects of bleaching due to their reliance on coral as a food source. The study found that after the bleaching event, different species of butterflyfish were able to resolve disputes by signaling just 10% of the time, indicating a significant increase in "unnecessary attacks."

Climate Change Threatens World's Coral Reefs

Human-driven climate change is causing mass coral bleaching as the world's oceans warm, threatening the future of the world's coral reefs. A modeling study conducted last year found that even if the Paris climate goal of holding global warming to 1.5 degrees Celsius is reached, 99% of the world's coral reefs will not be able to recover. At two degrees of warming, the number rises to 100%. Coral reefs provide vital habitats for a wide range of marine species and are also important for human communities, serving as a source of food and livelihood.

Butterflyfish: First to Feel the Effects of Bleaching

Butterflyfish, with their colorful patterns and reliance on coral as a food source, are the first to feel the effects of mass coral bleaching. When a mass bleaching event occurs, the butterflyfish's "food source is hugely diminished really quickly," according to Sally Keith, a marine ecologist at Lancaster University. The bleaching event in 2016 provided the perfect opportunity for Keith and her colleagues to study the impact on the behavior of butterflyfish, which they did by observing 3,700 encounters between the fish at 17 reefs off the coast of Japan, the Philippines, Indonesia, and Christmas Island.

Observations Show Decreased Ability to Resolve Disputes

The researchers observed that before the coral bleaching event, different species of butterflyfish were able to resolve disputes through signaling around 28% of the time. However, after the bleaching event, this number fell to just 10%, indicating a significant increase in unnecessary attacks. These attacks involve one fish chasing another, often until the chased fish gives up, and can lead to the expenditure of valuable energy that could potentially threaten the fish's survival.

Coral Bleaching Could Have Knock-On Effects on Other Species

The impact of coral bleaching on butterflyfish behavior could have knock-on effects on other species and up the food chain, according to Keith. It is not clear if the fish will be able to adapt to the changes brought about by coral bleaching quickly enough to avoid these negative impacts.

Conclusion

Mass coral bleaching, caused by human-driven climate change, is leading to increased fighting among fish and potentially threatening their survival. Butterflyfish, which rely on coral as a food source, are particularly affected by the bleaching, with their ability to resolve disputes through signaling decreasing significantly after a mass bleaching event. This increase in unnecessary attacks could have knock-on effects on other species and up the food chain. The future of the world's coral reefs is also at risk due to climate change, with even reaching the Paris climate goal of holding global warming to 1.5 degrees Celsius not enough to save 99% of the reefs.

Journal Information: Rapid resource depletion on coral reefs disrupts competitor recognition processes among butterflyfish species, Proceedings of the Royal Society B: Biological Sciences (2023). DOI: 10.1098/rspb.2022.2158. royalsocietypublishing.org/doi … .1098/rspb.2022.2158