Hot marine waves harm coral reef fish

Laila Ali

In the first study in the world to track how fish respond to extreme marine heat waves, marine biologists at the University of Hong Kong and the participating international team found that coral reef fish are directly affected by warming waves, and these responses vary greatly between different species.

The study, published in the journal Science Adventures on March 20, found that rapid warming of water causes an increase in fish metabolism, which is similar to what happens to an athlete who performs intense exercises, which affects the reproduction, growth and health of these fish.

Molecular approach to study
The study provides an approach to predict the types of fish most vulnerable under the conditions of repeated heat waves, by studying the molecular response of five different types of coral fish to the heat wave conditions of 2016 that killed a third of the coral reefs with the Great Barrier Reef in Australia.

Marine heat waves (MHWs) are high ocean temperatures for a long period of time, similar to the atmospheric heat wave.

The 2016 marine thermal wave was one of the longest and hottest heat anomalies, which affected multiple types of "variable-temperature" marine organisms, which relied on external heat sources to regulate their body temperature, including coral reef fish.

"We chose to work with five different species commonly found in coral reefs to be able to understand the differences in reactions between species of fish that have a life history," said Dr. Celia Schunter, a study participant from the University of Hong Kong's College of Biological Sciences and the Soire Institute of Oceanography. Different to get a broader view of influence and reaction. "

Gene expression changes
Through genetic analyzes, the team determined the specific physiological responses to warming by the different types of fish being studied, says Schunter. "Changes in gene expression can tell us how the animal physiologically responds to an environmental shock, such as a severe heat wave".

According to Dr. Moises Bernal, a study participant from Auburn University, the study results show that "when the water temperature rises, fish have greater demand for energy and oxygen, and increased demand for energy during warming can affect the reproduction, swimming and growth of these fish." , And for this reason it is important to understand the response to warming. "

"It is interesting that these patterns of gene expression have also changed with the duration of the heat wave," says professor Judy Romer of the ARC Center for Excellence in Coral Reef Studies at James Cook University and participating in the study. "This" indicates that the physiological mechanisms that fish use to deal with Warm water changes as the heat wave progresses. "

These results indicate that the impact of fish on the intensity of the heat wave and its duration, will lead to potential long-term consequences for fish health with increasing intense heat waves in terms of their frequency, duration and size in light of the climate change caused by humans.

Various responses
At the species level, Romer says the responses differed in severity, as some fish suffer less than others. Some fish respond strongly to warmer conditions through changes in the expression of thousands of genes, indicating that they are particularly sensitive to extreme heat waves. Other species appear more tolerant, as they have shown fewer changes in gene expression.

The study's associate professor, Timothy Ravasi, of the Marine Climate Change Unit at the Okinawa Institute of Science and Technology (OIST), says the study's findings "have implications for policymakers and the fishing industry, because all species will not be affected equally."

"We need to examine a large number of species to predict the most sensitive types, and others that will be better able to withstand high water temperatures and extreme heat waves," he added.

"Over time, fish may adapt to higher temperatures, or even migrate to cold water," Ravassi asserts, "but these hot waves are occurring now, and it is necessary to understand and study the direct consequences to them."