Coral reef snapper feeling impacts of marine heat waves on Great Barrier Reef

The fate of a popular fish found on the Great Barrier Reef could be in jeopardy, with a new James Cook University study highlighting the impact of marine heat waves on the Spanish Flag Snapper.

JCU researchers have discovered that while the species, commonly known as “Stripeys,” can recover from the effects of sharp rises in water temperature, catch-and-release fishing during these events may significantly impact their health and survival rates.

The study, led by former JCU Ph.D. student Shannon McMahon, collected mature adult Stripeys between Cairns and Cape Melville before transporting them to Townsville to simulate marine heat waves (MHW) across twelve 2500L outdoor tanks. The work is published in the journal Conservation Physiology.

“We all know that coral reefs are particularly susceptible to marine heat waves, which cause mass coral bleaching and mortality, but there was a real knowledge gap in the effects of MHW on coral reef fish,” Dr. McMahon said.

“Our results show that marine heat wave conditions cause direct physiological demands on adult coral reef snapper and residual effects can last for at least two weeks post these events. During a heat wave the fish are under a lot more metabolic stress, and we found that producing more hemoglobin was one coping mechanism during these events.”

Dr. McMahon said the species energetic needs were shown to increase up to 37 percent during MHW conditions.

“Climate change has led to the increasing frequency and intensity of MHWs, so there is an immediate need to understand the sensitivity of organisms both during and following these events,” he said.

Dr. McMahon, who is currently a Postdoctoral Scholar at Okinawa Institute of Science and Technology, said the increased demand for food from Stripeys could lead to increased predation of smaller reef organisms, which would have flow-on effects to wider reef ecosystems.

“If they can’t keep up their food intake to meet these stresses, these increased energy demands could mean a trade-off by decreasing other activities like growth or reproduction, which might influence population dynamics,” Dr. McMahon said.

“Fishing or capture puts them under pressure and when they are more vulnerable and really heat stressed, they could die easier following a catch and release.”

He went on to say that fishing restrictions during marine heat waves or advancement in catch and release protocols should be considered to limit or alleviate the effects on Stripeys and similar species.

“Further research on other coral reef fishes would give us a better idea of the effects future marine heat waves may impose on these vital ecosystems,” he said.

The paper was co-authored by JCU’s Marine Biology and Aquaculture Adjunct Professor Philip Munday and Associate Professor Dr. Jennifer Donelson.

Associate Professor Donelson said the study would help researchers better understand how larger reef fish responded to climate change, especially as marine heat waves continue to increase in frequency and intensity.

“Shannon’s passion for working on larger species of fish really drove his Ph.D.,” she said. “There hasn’t really been much research like this done on these larger reef fish before as they need big, purpose-built tanks but despite the challenges we were able to achieve original results at JCU Marine and Aquaculture Research Facility.”