Clownfish in Kimbe Bay, Papua New Guinea, were found to shrink in size during a major marine heat wave in 2023, according to a study published in Science Advances. Researchers observed 134 clownfish and reported that 101 of them reduced their body length at least once due to heat stress. Rising ocean temperatures, caused by climate change, are leading to more frequent and severe marine heat waves. These conditions harm coral reefs and sea anemones, which are essential shelters for clownfish. The study suggests that shrinking may help the fish survive by lowering their energy needs, as smaller bodies require less food.

Scientists believe the clownfish might reduce their bone mass to shrink. Some breeding pairs were seen adjusting their size together, with females staying larger than males. This helps maintain the social structure, as female clownfish typically lead the group. This behavior had not previously been recorded in coral reef fish. Researchers also found that the clownfish returned to their original size once temperatures normalized. This shows that the fish have biological flexibility. However, ocean experts warn that this strategy may not work if heat waves continue to grow longer and more intense. The study highlights both the adaptability and the limits of marine animals facing a warming climate.