How fear of sharks can influence seaweed growth

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How fear of sharks can influence seaweed growth

November 27, 2017 - 19:12
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The presence of sharks can indirectly alter coral reefs, according to a study.

A new study by scientists from the Bigelow Laboratory for Ocean Sciences describes how the presence of sharks has helped shape shallow reef habitats in the Pacific.

Simply put, a situation called trophic cascade comes into play in which the sharks’ presence discourages algae-eating fish (their prey) from frequenting certain areas, so as to avoid being eaten. This in turn allows the seaweed in those areas to flourish.

“This is the first location where we’ve determined that sharks are not just a passenger in the ecosystem but actually shape the way it looks and functions,” said lead author Doug Rasher, a senior research scientist at the institute. The findings of the study was published in the recent issue of the journal Scientific Reports.

The scientists focused their research on a shallow intertidal habitat in Fiji. At high tide, it is accessible to predators like the sharks from the nearby deeper waters. However, the area turns into a series of isolated lagoons at low tide, free from predators.

Using environmental monitoring and experiments, it was observed that the fish preferred to feed during low tide—when predators were not around. This kept seaweeds at a minimum in those areas. Alternatively, the seaweed flourished at the very top of the reef, which was accessible only during high tide when predators were about.

Describing the fear of predation as a powerful force in nature, Rasher commented: “Every animal on the planet would rather miss lunch than be lunch, so their actions often reflect that sentiment.”

He concluded, “We need to refocus the conversation away from whether trophic cascades generally exist and toward identifying the specific times and places that sharks shape the environment around them.”

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