The warming of the planet is causing the waters of seas and oceans to warm as well, affecting the life and behaviour of the many species of fish that inhabit them.
A study conducted in the Baltic Sea reveals that predatory fish are favouring the hunting and consumption of prey that are more abundant in the warmer waters. While this provides access to an immediate source of calories, the predators may be jeopardising their long-term health and survival, since the more abundant prey tend to be smaller and thus less calorific.
In an article published in the journal Nature Climate Change, researchers from Germany, the United Kingdom and Finland argue that these fish need to consume more calories when the waters are warmer, because higher temperatures raise their metabolism and, thus, energy loss. But, in the absence of more calorific prey, predators are limited to the most abundant, yet less suitable to their energy needs.
Therefore, they warn that the warming of seas and oceans could result in an increase in extinctions of predatory fish species, even if they are able to adapt their hunting behaviours to include other prey beyond those they are used to consuming. Despite the flexibility they may demonstrate, everything points to them becoming more vulnerable to the effects of climate change.
Benoit Gauzens, the first author of the study, explains in a press release that it is assumed that fish can adapt their food-searching behaviours to maximise calorie intake. However, “these results suggest that fish – and also other animals – may respond to the stress caused by climate change in ways that are unexpected and inefficient.”
The work consisted of analysing data, collected between 1968 and 1978, on the stomach contents of several Baltic Sea fish species, such as the European flounder (Platichthys flesus), and they concluded that, indeed, there seems to be a shift in prey preferences as the waters become warmer, from the less abundant, and more calorific, prey to the more abundant, but less calorific, prey.
Photo: German Centre for Integrative Biodiversity Research (iDiv)
Halle-Jena-Leipzig
“The fish species in the Baltic Sea, and elsewhere, are facing a multiplicity of pressures caused by humans, such as overfishing or pollution,” comments Gregor Kalinkat, another of the authors. And the shift in prey preferences could be an additional factor that could hamper the recovery of several fish populations.
Adaptation to environmental conditions, such as changing the way they hunt and the selection of prey, “tends to be a key for maintaining high levels of biodiversity in ecosystems,” says Gauzens, “so it is intriguing to see that this may not be entirely true in a context of rising temperatures.”
