Damsels in Hot Water

Lemon Damselfish over stony corals on the Great Barrier Reef. Image courtesy Australian Institute of Marine Science.

Small within-day increases in temperature affects boldness and alters personality in coral reef fish

For the first time, researchers have documented coral reef fishes becoming more aggressive as water temperature rises. In experiments at the University of New South Wales in Australia, wild-caught juvenile Lemon Damsels, Pomacentrus moluccensis, became markedly more fiesty and fearless when water temperatures were raised up to 3C (5.4F).

Not all fish behaved the same, but the personalities of some fish changed dramatically, with boldness and aggressiveness jumping 2.5 to 6 times as high as at lower temperatures.

Coral reef fish can undergo a personality change in warmer water, according to an intriguing new study suggesting that climate change may make some species more aggressive and bold.

Experiments with two species of young damselfish (Pomacentrus moluccensis and P. bankensis) on Australia's Great Barrier Reef have shown for the first time that some reef fish are either consistently timid, or consistently bold, and that these individual differences are even more marked as water temperatures rise.

A slight lift of just one or two degrees may have only a small effect on some fish but the behaviour of others can be transformed – leading them to become up to 30 times more active and aggressive.

Personality Changes

"The idea that fish have personalities may seem surprising at first, but we now know that personality is common in animal populations, and that this phenomenon may have far-reaching implications for understanding how animals respond to ecological and environmental challenges," says Dr Peter Biro, right, of the UNSW School of Biological, Earth and Environmental Sciences, who led the study with colleagues Christa Beckmann and Judy A. Stamps. It is published in the journal Proceedings of the Royal Society B.

"Our results also suggest that temperature variations are much more significant than we thought in the way they affect the behaviours of individual animals. This needs to be taken into account for scientific studies of other cold-blooded animals, or ectotherms, such as reptiles and amphibians.

"For instance, individual variations in activity and boldness can affect food acquisition, encounter rates with predators and even the likelihood of an individual being captured by sampling or harvesting gear.

Normal Fluctuations

"We observed that most of the individuals in our experiments were very responsive to changes in temperature, dramatically increasing their levels of activity, boldness and aggressiveness as a function of increases of only a few degrees of temperature. Fish would experience such temperature fluctuations during the course of a normal day."

The scientists used fish that were captured just as they were ending their larval stage in open water and had not yet settled onto the reef, and so were naive to social hustle and bustle of reef fish life. They then directly manipulated water temperatures in laboratory tanks at Lizard Island Research station.

Placed by themselves in tanks, the fish were free to explore or to take refuge in a short piece of plastic pipe. The scientists observed how far and how often the fish ventured from the pipe. In cooler water, individual fish differed greatly in their activity levels. They all became more active to varying degrees when the water was warmed, with some individuals becoming up to 30 times more active, bold and aggressive.

Concludes Biro: "Our results suggest the possibility for increasingly disrupted patterns of behaviour in fishes and other ectotherms under a scenario of climate warming, with increases in mean-level activity, boldness and aggressiveness of a magnitude that has been shown to result in greater vulnerability to predation, and decreased survival in other fish populations." (Biro et al. 2007)

Peter A. Biro recently joined the faculty of the University of New South Wales as a recipient of one of seven Australian Research Council Future Fellowships awarded to UNSW. The Australian Government created the fellowships to promote research in areas of critical national importance to attract and retain the best and brightest mid-career researchers to work in Australia.

Full Text of Paper in the Proceedings of the Royal Society B, January 10, 2010.

Credit: From information released by the University of New South Wales, Australia. Further information: University of New South Wales.

Image credit: Australian Institute of Marine Science (AIMS)