Study Finds Parrotfish Stayed Put During Extreme Marine Heatwaves in Eilat

A new five-year study in the Gulf of Eilat found that parrotfish, one of the reef’s most important fish families, barely changed their behavior during marine heatwaves. The researchers tracked 31 parrotfish from five species and saw that they did not move to cooler depths, reduce activity, or leave their habitats, even as water temperatures rose.

The work was led by Dr. Rannanel Pikeholtz and doctoral student Dan Baz Golanski from Prof. Jonathan Belmaker’s lab at Tel Aviv University, based in the School of Zoology, the Faculty of Life Sciences, and the Steinhardt Museum of Natural History. Using acoustic telemetry, the team implanted tiny transmitters in fish collected under permit from the Nature and Parks Authority, then released them and monitored depth and activity before, during, and after 12 separate marine heatwave events.

Parrotfish are known as the “gardeners” of coral reefs because they eat algae growing on rock, preventing it from overtaking corals. The researchers expected the fish to seek cooler water or conserve energy as metabolism rises in warmer water, but instead found almost no behavioral response. Golanski said the findings point to “a much more complex reality” that highlights the challenges climate change poses to marine ecosystems.

The scientists warn that the apparent calm may conceal “hidden vulnerability.” During the study period, a rapid warming event in Eilat caused widespread parrotfish deaths, suggesting the fish may suffer severe physiological stress without obvious warning signs. The results mirror studies from the University of Hawaii, where similar fish showed little behavioral change but did show stress and loss of body mass in physiological tests.

Dr. Asaf Zvoloni, Eilat Gulf ecologist at the Nature and Parks Authority, said the findings are concerning because parrotfish are critical to reef balance and may be nearing a tipping point before damage is visible. Since marine heatwaves cannot be prevented or the gulf cooled in the near term, he said the key is reducing local pressures through habitat protection, pollution prevention, strict fishing enforcement, and avoiding physical damage to the reef.