Fish give up battle after coral bleaching

The researchers found that when the water temperature of the corals warms up, the fish cool down, which is the first clear evidence that coral bleaching is the trigger for a rapid change in the behavior of the corals. reef fish.

Publication in Nature Climate change This week, researchers from Lancaster University and collaborating institutes, including the ARC Center of Excellence for Coral Reef Studies (CorE CoE), show how the iconic butterfly fish, considered as a sensitive indicator of reef health, can be a harbinger of people's struggles.

The international team of researchers spent more than 600 hours under water observing the butterfly fish over a two-year period encompassing the unprecedented coral bleaching event in 2016. The team led by Dr. Sally Keith of Lancaster University, previously Center for Macroecology, Evolution and Climate, examined 17 reefs located in central Indo-Pacific, Japan, the Philippines, Indonesia and Christmas Island (Indian Ocean).

During the initial data collection, researchers were unaware that catastrophic bleaching was on the horizon. Once launched, researchers realized that this fortuitous "natural experiment" put them in a unique position to see how fish changed their behavior in response to a large-scale disruption of bleaching.

The team mobilized to repeat their observations in the field and collected a total of 5,259 encounters between individuals belonging to 38 different species of butterfly fish. One year after bleaching, it was clear that even though the same number of butterflyfish continued to reside on the reefs, they behaved very differently.

"We have observed that the aggressive behavior of butterfly fish has decreased by an average of two-thirds, with the largest declines on reefs where bleaching has killed the most corals," said Dr. Keith. "We think this is due to the fact that the most nutritious coral was also the most sensitive to bleaching so the fish went from a balanced diet to the equivalent of eating only lettuce leaves. It was enough to survive rather than prosper. "

Nathan Sanders, ecologist and co-author of the University of Vermont, said: "This is important because butterfly fish are often referred to as the" reef canaries "because of their heavy reliance on fish. the coral, they are often the first to suffer after a disturbance. "

Such behavioral changes may well be driving more obvious changes such as decreasing the number of fish individuals and species. This discovery could help explain the mechanism behind the population decline in similarly disturbed ecosystems around the world.

"Our work emphasizes that animals can adapt to short-term disasters through flexible behavior, but that these changes may not be sustainable in the long term," said co-author Andrew Baird. from Coral CoE to James Cook University.

Explore further:
Coral bleaching threatens diversity of reef fish

More information:
Sally A. Keith et al., Synchronous behavioral changes in reef fish associated with massive coral bleaching, Nature Climate change (2018). DOI: 10.1038 / s41558-018-0314-7