Photo: Pixabay/j981511225

Ecosystems are delicately balanced biological arrangements and the disappearance of even seemingly minor species within them can have grave knock-on effects.

A case in point, say scientists, is the precarious balance that prevails at coral reefs worldwide between predatory fish and their prey.

These predators choose their prey more carefully than previously thought and do not just gobble down any fish they encounter at reefs, according to researchers from France and the United States who analyzed the stomach contents of most fish species found on six coral reef systems around the world.

In all, the scientists examined the feeding habits of more than 600 species found on six coral reefs near Okinawa in Japan, Hawaii in the US, the West Indies, New Caledonia, Madagascar and the Marshall Islands.

Notwithstanding the great geographical distances, the food webs at all six reefs were highly similar in their makeup: even in the face of plenty of other available food items, two-thirds of the predatory species examined proved to be specialized feeders that displayed a strong preferance for specific prey animals.

The findings, published in a study, indicate that food webs at the world’s reefs are more delicate than widely assumed because the loss of a single larger fish species may throw off a reef’s entire ecosystem.

“It’s remarkable that we see similar patterns in coral reef systems all over the world. Extinctions, particularly of larger fish species, may have significant impacts for coral reef systems,” stresses Jordan Casey, an assistant professor of marine science at the University of Texas Austin’s Marine Science Institute.

This is disconcerting as overfishing targeting larger fish at coral reefs can deplete the numbers of these fish, especially in tandem with other stressors such as climate change and water pollution.

That is why protection measures at reefs needs to be holistic in their scope.

“Reefs rely on the efficient utilization of all creatures,” said Simon Brandl, an assistant professor. “If a fish specializes on eating a certain type of snail and that fish disappears, the snail might not be eaten and live happily ever after. This creates a dead end for the food it could provide to other coral reef creatures. Good news for the snail. Bad news for everything else living there.”

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