Clownfish are known for their symbiotic relationship with sea anemones. They are also famous in pop culture, thanks to the movie ‘Finding Nemo’, where the protagonist was a clownfish named Nemo. Now, researchers have noted that clownfish shrink in order to survive marine heatwaves and social conflicts. The universities of Newcastle, Leeds, and Boston participated in the research. This research was conducted with the help of the Mahonia Na Dari Conservation and Research Centre, in Kimbe Bay, Papua New Guinea.
The team measured the length of 134 clownfish every month over a span of five months. The team also kept track of the water temperature every 4-6 days during a marine heatwave, a period during which the temperature of the sea surface is higher than usual. Marine heatwaves are becoming increasingly common due to climate change and global warming. In response to this heat stress, the clownfish shrink and get shorter.
Individuals who shrank had greater chances of survival during heat stress. The chances of survival increased by 78% after shrinking. Another discovery shows that the chances of survival increase if a clownfish shrank alongside its breeding partner. This is the first time a coral reef fish has changed its length to adapt and survive through environmental and social conditions. Among the 134 fish whose length were measured, 100 fish shrank in size.
The study was led by Melissa Versteeg, a PhD researcher at Newcastle University’s School of Natural and Environmental Sciences. According to her, “This is not just about getting skinnier under stressful conditions, these fish are actually getting shorter. We don’t know yet exactly how they do it, but we do know that a few other animals can do this too.” She cites the example of iguanas that can reabsorb some of their bone material to shrink in size in response to environmental stress. The fish have surpassed expectations and have surprised the researchers with their ability to adapt to a changing environment. They were also extremely flexible in regulating their sizes, both as individuals and as breeding pairs, making them adept at surviving heat waves.
According to the authors, individual shrinking might explain the decrease in the size of fish in the saline oceans. According to Dr Theresa Rueger, Senior Lecturer in Tropical Marine Sciences and senior author of the study, individual shrinking in fish in response to heat stress can improve the chances of survival. The change in size is also impacted by social conflict.
Further studies are needed in this field to see if other fish species are also individually losing out on the extra few centimeters. If discovered in different fish species, it could provide a hypothesis regarding the declining size of various fish.
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