Heat wave forces clownfish to shrink – survival strategy discovered!

Heat wave forces clownfish to shrink – survival strategy discovered!

The effects of climate change on marine wildlife are not just an abstract concept, but are concretely reflected in the changes in the behavior and physiology of living beings. A recent study published in the journal “Science Advances” impressively sheds light on how clownfish react to extreme water temperatures. A research team from Newcastle University analyzed 67 wild clownfish pairs in Kimbe Bay, Papua New Guinea. During a five-month heat wave from February to August 2023, in which water temperatures rose an average of four degrees above normal, 100 of the 134 fish examined shrunk.

Around 44% of these fish shrank by a few millimeters, while 30% shrank several times. Only about 25% remained unchanged. What was striking was that there was no difference in shrinkage between rank or gender, but a couple effect was observed: the shrinking of one partner had an influence on the other. These coordinated adaptations appear to reduce friction in the fish's hierarchical relationship, improving their chances of survival during the heat phase. In fact, the shrinking fish were up to 78% more likely to survive, while 11 fish died during these very stressful conditions.

Fish size and climate change

Research shows that as water temperatures increase, fish's oxygen requirements also increase, while there is less dissolved oxygen in the water. This leads to shrinkage being an energetic strategy to survive in superheated water. However, these adaptive mechanisms are not just limited to clownfish; Similar shrinkage processes have also occurred in other species, such as marine iguanas. It is suspected that these developments in fish size can also be observed in seas affected by climate change.

Fishing could further exacerbate the problem. A WWF report shows that the oceans play a central role in the global climate by producing oxygen and absorbing carbon dioxide. Climate change is increasing challenges for marine ecosystems, which has negative impacts on fisheries. Rising water temperatures and higher carbon dioxide levels lead to warmer and more acidic water, which greatly disrupts fish behavior and feeding. Projections show that 99% of coral reefs could die by the end of the century, which would be devastating for many marine life.

Consequences for fisheries and food security

Smaller and less catchy stocks represent an immediate threat to fishing. Scientists estimate that each additional degree Celsius of warming could lead to a decline in global fishing potential of over 3 million tons. Developing countries in particular, where over two thirds of the population rely on sea fishing, are severely affected. A 50% reduction in catch levels is expected by 2050, which could have a dramatic impact on the protein-rich diets of these regions.

To address these challenges, sustainable fisheries management strategies and innovative aquaculture approaches are crucial. Scientists emphasize that improved management of fish stocks could increase fish biomass by up to 60% if global warming is controlled. The WWF therefore recommends treating fish as a delicacy and paying attention to sustainable sourcing practices to reduce the ecological footprint and protect marine biodiversity.