How shifting light patterns protect prey on Great Barrier Reef

17 April 2020



In an international collaboration, Queensland Brain Institute (QBI) researchers have helped scientists from the University of Bristol uncover how shifting light patterns help protect fish from predators on the Great Barrier Reef.

Professor Justin Marshall from QBI and Dr Karen Cheney from UQ’s School of Biological Sciences – working with the University of Bristol researchers – showed how ripple-patterns, known as ‘water caustics’, masked the movements of fish on the reef.

The research team trained the reef triggerfish (Rhinecanthus aculeatus), a common fish around the Lizard Island Research Station, to locate and attack moving prey presented within computer-simulated scenes.

Each scene contained water caustics that varied in terms of motion (static or moving), scale (fine or coarse) and sharpness (sharp or diffuse), illustrative of the diversity seen in natural habitats.

The results showed that if the light patterns remained static, the window of opportunity for the triggerfish to attack significantly increased. In other words, the fish could easily see the target and get a food reward.

However, when caustics or ripples were inserted in the scene, as would be found in shallow water in nature, the fish took longer in locating the target.

Dr Sam Matchette, a former PhD student at the University of Bristol and the lead author, said the findings highlighted conditions that proved staying still wasn’t the only defence for prey.

“Our investigation is the first to address the impacts of dynamic underwater illumination upon fish behaviour and directly assess how visual features of water caustics can affect visually guided behaviour,” Dr Matchette said.

“Due to the direct impact upon foraging efficiency, we predict that the presence of dynamic water caustics will have important consequences for decision-making regarding habitat choice and foraging by both wild prey and predators.”

The research was supported by the Australian Research Council, a CASE studentship and research grant from the Engineering and Physical Sciences Research Council (EPSRC) and QinetiQ.