What If There Were No Sharks?

Sharks are magnificent predators that represent an impressive evolutionary success story. They’ve swum the oceans for more than 400 million years, diversifying over time to inhabit rivers and lakes as well. About 500 known species are alive today, and there are likely even more yet to be discovered.

Sharks can be huge, like the massive whale shark (Rhincodon typus); or human-hand-size, like the pocket shark (Mollisquama parini). However, it’s the great white shark (Carcharodon carcharias) that typically commands the public’s imagination. These sharks have a reputation for aggressiveness toward people, shaped by decades of terrifying portrayals in movies. In fact, these fearful pop-culture portraits of great whites are so pervasive that they might lead some people to wonder if the world would be better off with no sharks at all.

But what might the oceans look like if all of the sharks disappeared?

Sharks make their homes in ecosystems around the world, including shallow mangrove habitats, tropical coral reefs, frigid Arctic waters and the vastness of the open ocean. Regardless of where sharks live or how big they are, all of them are predators and, therefore, are vitally important to the health of their habitats, said Jenny Bortoluzzi, a doctoral candidate in the Department of Zoology at Trinity College Dublin in Ireland.

Fish-hunting sharks weed out weak and sick individuals, ensuring that the fish population remains healthy and at a size that the habitat’s resources can support. These fearsome predators can even help to preserve their ecosystems through their presence alone, Bortoluzzi told Live Science in an email. For example, tiger sharks (Galeocerdo cuvier) that live in seagrass meadows scare away turtles and keep them from overgrazing the vegetation, she explained.

Sharks also play a role in regulating oxygen production in the ocean, by feeding on fish that devour oxygen-generating plankton, Victoria Vásquez, a doctoral candidate with Moss Landing Marine Laboratories in California.