Ocean currents bring good news for reef fishes

JCU PhD candidate Renato Morais from JCU’s Centre of Excellence for Coral Reef Studies led a study that looked at how fishes on a bleached coral reef get their food.

“We already knew that coral reef fish rely on food drifting in from the sea, such as plankton. But we didn’t know exactly how important this was for fishes,” he said.

Mr Morais and JCU’s Professor David Bellwood combined high-resolution surveys and individual biomass production estimates to generate the first map of where the energy comes from for all fishes on a coral reef.

“We looked at everything from gobies to coral trout and large jacks, assessing more than 18,000 fish from over 300 species. We found that various transport mechanisms, such as currents and tides, interact with the reef and bring in vast amounts of plankton,” said Mr Morais.

The pair found that, for every kilogram of fish produced on the reef, more than 400 grams of that kilogram relied on food derived from the open ocean, rather than the reef itself. This rises to almost 600 grams for fishes on the side of the reef facing the open ocean.

“This means, that for many reefs, food from outside can sustain fish populations, even when the coral is badly damaged,” said Professor Bellwood.

The scientists found that areas of the reef that were more exposed to the open ocean produced the largest quantities of fish – with reef slopes being the most fruitful.

“The discovery that reef fishes get so much of their food from off-reef sources was encouraging, especially because many fish species that feed on oceanic material have a history of disappearing after coral loss,” said Mr Morais.

“This is the first time we have been able to put all species in perspective,” said Prof. Bellwood. “Our study offers hope that reefs subject to coral loss can still be productive. The reefs may be damaged but they are still incredible valuable.”

Link to paper here.

Link to lab here.

Link to images here. (Please credit as marked with agency and photographer. All images are provided on the basis of a one-time use in conjunction with this press release only. They are not available for re-use or archiving. Copyright remains with the author).