The world needs coral reefs, and coral reefs need sharks

Grey reef sharks swimming among convict surgeon fish. Fakarava, French Polynesia © Paul Mckenzie / WWF
Caribbean reef shark with barrel sponge. Roatan, Bay Islands, Honduras, Central America © Antonio Busiello / WWF-US

Restoring depleted and declining reef shark populations will require that fishing pressure be reduced, and off limits in some areas or in some seasons. With care, this should benefit other large fish like the groupers and large jack, and since these are important food fishes, this would benefit coastal communities too.

Putting these findings into context requires understanding what should be there — the natural abundance of sharks on coral reefs. It turns out that this is higher than you might imagine, and certainly way higher than my earliest dives 30 years ago would suggest. Historical data on sharks on coral reefs prior to WWII is practically non-existent, so scientists had to look at those most undisturbed by fishing instead.

Grey reef sharks swimming against the current beside a coral reef wall. Fakarava, French Polynesia © Paul Mckenzie / WWF
Bluespotted ribbontail stingray (Taeniura lymma). © Philipp Kanstinger / WWF

Efforts to minimize the threats to coral reefs, on which hundreds of millions of people depend, are rightly focused on reducing atmospheric greenhouse gases. But what if protecting sharks helped build the resilience of coral reefs?

While we don’t understand the full range of ecological roles that reef sharks play, they and coral reefs have co-existed for millions of years and it is highly likely that there are mutual benefits yet to be discovered — especially because shark numbers were so much higher in the past. For example, just 10 years ago it was not known that grey reef sharks assist in distributing nutrients around reefs by defecating nitrogen waste from fish they have eaten away from the reef. This nutrient input is important as coral reefs are generally nutrient poor, and thus these “top-ups” contribute to reef health (Williams et al. 2018).

Tiger shark swimming over a seagrass meadow in the Bahamas © Marion Kraschl / Shutterstock

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WWF Oceans

WWF Oceans

#Ocean Practice @WWF 🐼 Working to protect and restore ocean health for the benefit of people, nature and climate. Not all RTs are endorsements.