This article has been reviewed according to Science X's editorial process and policies. Editors have highlighted the following attributes while ensuring the content's credibility: Marine heat waves and anemone bleaching are altering clownfish behavior, making clownfish more defensive of their host and more aggressive toward one another, new research reveals. Led by Newcastle University and published in the journal Royal Society Open Science, the study explores how clownfish behavior changed during the 4th Global Bleaching Event.
During this event, the clownfish experienced a heat wave and their anemone partners bleached, meaning they lost their symbiotic algae, a stress response to elevated temperatures. The results indicate that while elevated temperatures only had a small effect on clownfish behavior, the bleaching response of the anemone altered how the animals spent their time. Bleaching led to more defensive behaviors, which could benefit the host anemone, and aggression between group members increased.
A group of Newcastle University students, led by Ph.D. candidate Fletcher Noble, measured fish behavior from video recordings made during a marine heat wave in Kimbe Bay, Papua New Guinea, that lasted from March to July 2023. These were made during the most extensive and intensive mass coral bleaching event in recorded history, spanning from 2023 to mid-2025 and known as the 4th Global Coral Bleaching Event. The team analyzed five behavioral categories: maintenance and defense, which help the anemone partner; and aggressive, neutral and submissive behaviors, which maintain the fishes' social group.
Their findings show that bleaching did not alter the large amount of maintenance behaviors toward the anemone that clownfish displayed, such as aeration and cleaning, while defense behaviors increased. This emphasizes the crucial role of mutualism between anemonefishes and anemones, where each partner depends on the other for defense against predators and nutrients. The aeration and defense done by clownfish during bleaching events may be important for anemones to recover from bleaching.
The potential trade-off, however, is that social cohesion may suffer in times of stress. Bleaching was linked to a 215% increase in aggressive behavior between members of the clownfish social group. Study lead author Noble, a Ph.D. researcher at Newcastle University's School of Natural and Environmental Sciences, said, "This research is one of the first to examine in detail how different types of clownfish behavior change under bleaching conditions in the fish's natural environment.
"We revealed that clownfish are prioritizing defending and maintaining their homes and securing their dominant position in the group during periods of environmental stress. In the future, we can examine these behaviors in even greater detail and explore how this may be helping the anemone recover from bleaching." Discover the latest in science, tech, and space with over 100,000 subscribers who rely on Phys.org for daily insights. d research that matter—daily or weekly. Anemone bleaching occurs due to the loss of symbiotic algae and may turn the animal pale, white or translucent.
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