I should not be surprised when research reveals something amazing about topic I was previously not all that interested in. But when researching sharks recently, I was once again surprised.

Leopard Shark

Photo Credit – Eric Heupel

The word “shark” likely conjures up an image of a great white. And yet there are more than 500 species of sharks that come in all shapes (think hammerhead shark) and sizes. There’s the aptly named dwarf lantern shark which is the size of a human hand. Then there are whale sharks that grow to 40 feet long (roughly the size of a school bus).

Sharks live in oceans around the world in a variety of marine habitats from coral reefs to deep open water and even under Arctic ice. But what is perhaps most interesting about sharks is that they are keystone species. As apex predators, their job is to hunt, which keeps their prey populations in check. Without them, ecosystems become unbalanced. For example, the number of sharks in the ocean near Australia dropped. As a result, the grouper population grew because fewer sharks were around to eat them. But the grouper eat the fish that eat algae. So without the algae-eating fish, coral reefs were smothered and struggled to survive.

A different example of sharks’ role as a keystone species is the tiger shark. They hunt in shallow waters near seagrass looking for birds, turtles, stingrays, and more. But when the sharks are lurking, prey animals skedaddle. This limits how much time these prey animals spend grazing in an area which prevents overgrazing. Thus more seagrass grows. For coastal communities this is an essential ecosystem service because seagrass helps prevent erosion.

Finally, sharks eat unhealthy and injured animals, removing the weakest animals and allowing only the healthiest ones to reproduce. And by eating diseased animals, sharks keep disease from spreading. So next time you hear the word “shark,” try not to think of a toothy, fearsome predator, but of marine ecosystem managers.