Less Fish Stress For Youngsters When Big Barrier Reef Predators Nearby

By on April 28, 2016
Fish swim along the Great Barrier Reef. (Credit: Flickr User Robert Linsdell via Creative Commons 2.0)

The makeup of food chains can affect all sorts of dynamics for fish. For the younger ones, scientists at James Cook University have even found that it can play roles in fish stress.

According to the researchers, baby fish have higher stress levels when fewer big predators are around. On the other hand, when there are more of these large predators around, the young fish feel more relaxed. So how could that be?

Scientists believe that the presence of larger predators helps to drive off the smaller predators that prey on young fish. And with their main pursuers, called mesopredators, essentially afraid to venture out too much, baby fish feel like they can relax.

To make the findings, researchers at the university exposed baby damselfish to combinations of sensory cues including visual and scent cues from small and large predators. From there, the scientists measured the amounts of oxygen that the fish took up as an indicator of their stress levels. Effects on the fishes’ behavior were recorded as well.

Taking this approach allowed scientists to understand the cascading effects that predators throughout the food chain can have on newly settled baby fish on the Great Barrier Reef. They say that this study is the first to show that controlling mesopredators is enough to reduce stress levels for baby fish along the reef by more than 35 percent.

These reductions can help to benefit the fitness and wellbeing of the fish because less stress means they can devote more energy to growing and storing food for survival. Results of the study also indicate the importance of having ecosystems complete with the right mix of large predators, mesopredators and the other, smaller creatures that they prey on.

For instance, researchers say that the ongoing overexploitation of large marine carnivores might allow an explosion of smaller, active predators that could not only kill, but also stress the populations of baby fish that remain.

Full results of the study are published in the Journal of Animal Ecology.

Top image: Fish swim along the Great Barrier Reef. (Credit: Flickr User Robert Linsdell via Creative Commons 2.0)

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