According to a recent study Nature Climate ChangeFish are adapting their hunting and feeding patterns in response to rising ocean temperatures; According to models, this change could increase the likelihood of extinction.

Led by researchers from the German Center for Integrative Biodiversity Research (iDiv) and the Friedrich Schiller University of Jena, researchers discovered that fish in the Baltic Sea respond to rising temperatures by eating the first prey they encounter. This change in foraging behavior caused the fish to choose larger and smaller prey. Small prey found in their environment at all temperatures included brittle stars, small crustaceans, worms, and molluscs.

Fish, like many other consumer species, need more food when temperatures rise because their metabolism also increases. Although abundance of prey provides an immediate energy source, this so-called flexible foraging behavior means that fish lose the ability to meet their long-term energy needs by consuming larger prey that provide more calories.

Model food web calculations show that this mismatch between fish’s energy needs and their actual food intake could lead to larger extinctions in hot conditions, where fish would eventually starve because they did not eat enough to meet their energy needs. The model, which can also be applied to other types of consumers, suggests that this is especially true for species higher up the food chain. Overall, the authors suggest that this flexible foraging behavior may make communities more vulnerable to climate change.

“It is generally assumed that species adapt their foraging to maximize the amount of energy they consume,” explains first author Benoit Gauzens from iDiv and the University of Jena. “But these findings suggest that fish, like other animals, may respond to climate change stress in unexpected and ineffective ways.”

Fish stomach data

Researchers analyzed ten years of data on the stomach contents of six commercially important fish species with different feeding strategies in the Bay of Kiel. For example, halibut such as European halibut (Platichthys flesus)Atlantic cod tend to be sit-and-wait predators (Gadus morhua) we are more actively searching for food. These data, collected throughout the year from 1968 to 1978, allowed us to understand how fish eat (what’s in their stomachs) and what prey is around them at different temperatures. Stomach contents showed that as the water warmed, the fish gradually shifted its focus from less abundant prey to more abundant prey.

“Fish in the Baltic Sea and elsewhere face numerous anthropogenic pressures, such as overfishing or pollution,” adds co-author Gregor Kalinkat from the Leibniz Institute of Freshwater Ecology and Inland Fisheries (IGB). “The impact of less efficient foraging behavior under warming conditions may be another, as yet unexplained, factor why fish stocks fail to recover even if fishing pressure is greatly reduced.”

Using these findings, the researchers calculated how this change in foraging behavior at different temperatures affects other species and the ecosystem as a whole, using mathematical food web models based on theoretical ensembles. The results show that this change in foraging behavior as temperatures rise leads to further extinctions of consumer species such as fish. These extinctions also have consequences for other species in the community.

“Adaptation of foraging behavior to local environmental conditions is often key to maintaining high levels of biodiversity in ecosystems,” adds Hausens. “So it’s surprising to see that in the context of rising temperatures, that may not be entirely true.”

Although impressive, the results of the data obtained are evaluated because they are based on theoretical models. In the future, researchers hope to test the mechanism in a natural environment and study different organisms to see whether they show similar or different changes in foraging behavior.