# Newcastle University: bleaching of host anemones raised clownfish aggression by 215% in Kimbe Bay

- Published: 2026-11-13 04:41 UTC
- Section: Life & Health › Biology & biochemistry
- Tags: clown anemonefish, Amphiprion percula, anemone bleaching, marine heatwave, Kimbe Bay, 4th Global Coral Bleaching Event, mutualism, clownfish aggression, Newcastle University
- URL: https://realtech.media/news/rt-b9ef97c11c6d1325c691db08_newcastle_university_bleaching/

**In a field observation in Papua New Guinea, anemonefish kept caring for bleached host anemones and defended them more, while aggression within their groups rose.**

![Newcastle University: bleaching of host anemones raised clownfish aggression by 215% in Kimbe Bay](https://realtech.media/media/2026/11/7f0185bf2444235c.jpg)
*Janderk, Wikimedia Commons, Public domain*

A team led by Newcastle University reported that bleaching of host anemones changed the behaviour of clown anemonefish, Amphiprion percula, during a marine heatwave in Kimbe Bay, Papua New Guinea. The heatwave lasted from March to July 2023. The results were published in Royal Society Open Science. Bleaching was linked to a 215% increase in aggressive behaviour between members of a fish social group [1].

## Field observation during the heatwave

Newcastle University students, led by PhD candidate Fletcher Noble, measured fish behaviour from video recordings made during the heatwave [1]. The heatwave fell within the 4th Global Coral Bleaching Event, which ran from 2023 to mid-2025. Some of the host anemones bleached and lost their symbiotic algae, while others did not. This let the authors separate the effects of heat stress itself from the indirect effects acting through stressed mutualistic partners [1].

The team analysed five behavioural categories. Maintenance and defence help the anemone partner. Aggressive, neutral and submissive behaviours maintain the social group of the fish.

## Anemone first, group second

Neither stressor significantly changed activity levels or interactions with the anemone, which made up a high proportion of all behaviours [1]. Maintenance behaviours such as aeration and cleaning of the anemone stayed at the same level, while defensive behaviours increased with bleaching [1]. Elevated temperature alone had only a small effect on behaviour. The bleaching response of the anemone altered how the fish spent their time [1].

The authors note that aeration and defence by the fish during bleaching may be important for anemone recovery. The possible trade-off is weaker social cohesion in the group [1]. According to Noble, the study is one of the first to examine in detail how different types of clownfish behaviour change under bleaching conditions in the natural environment. He said the fish prioritise defending and maintaining their homes and securing their dominant position in the group.

The work is an observational study. Senior author Theresa Rueger of Newcastle University's School of Natural and Environmental Sciences said that interactions between species, particularly mutualisms, should be considered when studying the effects of environmental change.

## Sources

1. [Royal Society Open Science](https://doi.org/10.1098/rsos.261623)
2. [EurekAlert](https://www.eurekalert.org/news-releases/1151139)

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Source: RealTech, realtech.media — https://realtech.media/news/rt-b9ef97c11c6d1325c691db08_newcastle_university_bleaching/