Clownfish Will Endure and Adapt to Rising Ocean Temperatures

To endure Rising ocean temperatures, clownfish adapt by decreasing their size.

Research has shown that various orange-striped fish shrink during heat waves off the coast of Papua New Guinea. These smaller fish are more likely to survive.

Climate change is causing heat waves to become more frequent and severe underwater. Elevated water temperatures can lead to the bleaching of the sea anemones that clownfish rely on, prompting them to adapt in order to survive.

During the severe heat wave of 2023, scientists tracked 134 colorful clownfish in Kimbe Bay, discovering that 101 of them exhibited significant reductions in length due to heat stress.

“We were genuinely surprised at first when we observed them shrinking completely,” remarked Morgan Bennett Smith, a research author at Boston University. The findings were published on Wednesday in the Journal of Science Advances.

Researchers are still unsure about how clownfish shrink, but one theory suggests they may be reabsorbing their own bone material. Smaller fish need less food, allowing Kakulfish to conserve energy during stressful conditions by becoming smaller.

Certain clownfish breeding pairs also exhibited synchronized contractions that improved their survival. The females maintained the social hierarchy and adjusted their size to remain larger than their partners, according to the researchers.

Additionally, other species are also shrinking in response to heat. For instance, marine iguanas reduce in size during El Niño events, which warm waters in the Galapagos. However, this coping mechanism has not been reported in reef fish until now.

“This is an additional strategy that fish employ to adapt to a changing environment,” said Simon Thorold, a marine ecologist at the Woods Hole Marine Facility who was not part of the research.

This strategy may help fish withstand heat waves in the short term, but it remains uncertain how they will cope if such conditions persist over the coming years, Thorold noted.

The researchers found that these reductions in size were temporary. Clownfish were able to “catch up” and grow again once the environment became less stressful.

“These natural systems are severely stressed, but they exhibit remarkable resilience,” Versteeg states.