Coral reefs are under immense pressure from climate change, pollution, and human activities. However, new research reveals an unexpected culprit in their decline: shark fishing. Scientists from The University of Western Australia’s Oceans Institute and the Australian Institute of Marine Science (AIMS) have found that removing sharks from reef ecosystems disrupts the food chain, leading to outbreaks of coral-eating crown-of-thorns starfish.

These starfish, in controlled numbers, help maintain coral diversity. But when their populations surge, they rapidly consume coral, accelerating reef destruction. According to Dr. Mark Meekan from AIMS, “Coral reefs around the world are in crisis, and outbreaks of crown-of-thorns starfish are seen as one of the key contributors.”

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Sharks Maintain Balance

Sharks play a crucial role in regulating marine food chains. Their presence keeps smaller predatory fish, such as snappers and emperors, hunting near the reef floor. These fish naturally prey on juvenile crown-of-thorns starfish, helping control their numbers.

Recent DNA studies confirmed that these smaller predators consume starfish, but the new research highlights how frequently this happens—and what occurs when sharks are removed. Without sharks, smaller fish venture into open waters, switching their diet to squid and smaller fish. The starfish they once consumed are left unchecked, leading to population explosions.

Dr. Lester explained, “When sharks are present, smaller species feed on seabed invertebrates like crabs and starfish. But when sharks are fished out, these predators move into open waters, growing faster while allowing invertebrate populations to surge.”

The Link Between Overfishing and Reef Decline

Areas with low fishing pressure, such as marine reserves, have significantly fewer starfish outbreaks. In contrast, reefs where shark fishing is common experience frequent starfish surges. Dr. Diego Barneche from AIMS emphasized that “overfishing, particularly of sharks, makes reefs more vulnerable.”

Beyond the starfish problem, losing sharks disrupts entire marine ecosystems, making coral reefs more fragile in the face of climate change and pollution. Scientists argue that protecting sharks is a cost-effective way to enhance reef resilience.

“We need to improve the resilience of coral reefs while facing climate change and pollution,” Dr. Meekan stated. “Reducing shark fishing may be a practical step to naturally regulate starfish outbreaks.”

A Call to Protect Coral Reefs

Coral reefs are among the most endangered ecosystems on Earth, with climate change being the dominant threat. However, this research underscores that human actions, such as shark fishing, can exacerbate their decline. The solution might be as simple as allowing sharks to fulfill their natural role—keeping reef ecosystems in balance.

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