Triops Longicaudatus
Triops Longicaudatus Red
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Triops Longicaudatus Red
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Clownfish defy ocean warming with an amazing trick
Inspired by nature: How clownfish adapt to heatwaves
The oceans are getting warmer and with them underwater life is changing dramatically. But clownfish react to extreme temperatures by simply shrinking. An astonishing survival mechanism that an international research team has now investigated in more detail.
In an elaborate long-term study published in the journal Science Advances, scientists observed 67 pairs of clownfish (Amphiprion percula) in the coral reef of Kimbe Bay in Papua New Guinea. The focus was on the effects of a heatwave in which the water temperature during the study period, from February to August 2023, was around four degrees above the long-term average.
The result was surprising: more than 70 per cent of the fish observed shrank in size over the course of the five months, in some cases several times. The animals shrank by several millimetres, a detail that may seem inconspicuous at first glance, but is of enormous biological importance. This is because as their body size decreases, their chances of surviving the heat improve, in some cases by up to 78 per cent compared to conspecifics that retained their size.
Fish-style couples therapy
The special thing about this is that the clownfish do not shrink on their own, but in synchronisation with their partner. Within a pair of fish, consisting of a dominant female and a smaller male, the body sizes changed synchronously. The balance within the social hierarchy was thus maintained. This, in turn, is crucial, as living together in clownfish is strongly based on clear hierarchies. If the size ratio is disturbed, this can lead to aggressive behaviour, expulsion or even fatal conflicts.
‘If you shrink, then I shrink too’ is how the researchers describe the observed phenomenon. A behaviour that not only avoids conflict, but also appears to have a life-saving effect.
Customisation with a system
The adaptation mechanism is multi-layered. In warmer water, the metabolic rate increases, while at the same time less oxygen is available. Larger fish then find it more difficult to absorb sufficient oxygen through their gills. A smaller body requires correspondingly less oxygen and therefore has an advantage. A possible decrease in food availability under heat stress could also play a role.
Although it is not yet fully understood exactly how shrinkage occurs physiologically, for example whether it is an active degradation of tissue or a kind of growth regression, the connection is clear: smaller clownfish live longer when the sea becomes a heat trap.
Growth with a return ticket
The researchers also observed that the animals increased in size again in synchronisation with improved environmental conditions. The adaptation therefore appears to be reversible, an astonishing demonstration of the flexibility of marine organisms in the face of changing climatic conditions.
These findings could also be important for nature conservation. This is because they show that even sensitive species such as clownfish have remarkable adaptation strategies. At the same time, the study makes it clear how severely marine organisms are suffering from global warming and that not every species has such sophisticated mechanisms.
Conclusion: The shrinking trick is more than a curious anecdote, it is an example of the silent intelligence of evolution in the fight against climate change.
