ology logo
card
180

continental shelf

OLogy Series
place
card
180

continental shelf

OLogy Series
place

Most ocean plants and animals live near the shore, on a narrow ribbon of seafloor called the continental shelf. These flat, shallow ledges gently slope from the shore to a steep drop called the continental slope. The shallow, sunlit waters of the continental shelf are flooded with nutrients, supporting an abundance of sea life. Many animals live here. Ninety percent of the world's fish are found along the continental shelf.

A Struggle for Survival
Georges Bank is a shallow underwater plateau off the coast of Maine. It once seemed that there was a limitless abundance of fish, lobster, and scallops in this fertile area. But populations are rapidly declining due to overfishing. Most of the danger comes from trawling, or dragging heavy nets over vast areas to catch fish. Not only does this practice kill large numbers of fish, but it also disrupts the ocean bottom, where many species do most of their feeding. Trawling stirs up muddy sediment, removing vital nutrients from the water. The heavy nets also crush the tunnels and tubes of small animals, which in turn destroys the food, homes, and hiding places of other animals. At one time, young fish found protection from the nets among the rocks. But in the late 20th century, rubber wheels were added to the nets so they could be dragged over rocks. Trawling has removed so many fish and destroyed so much habitat that the populations in Georges Bank have not been able to recover.

The shallow waters of the continental shelf are rich with nutrients. These nutrients come from:

runoff from the land

ocean currents

both A and B

Are you right?

Correct!

New nutrients are added to the continental shelf by runoff from the land and by currents from deeper out at sea. These nutrients, as well as sunlight, allow algae to grow, providing food for huge numbers of marine animals.

When ship nets are dragged over the seafloor, they clear about as much land annually as is cleared by logging.

Fact
or
Fiction
?

Fiction

About 150 times more land is cleared annually by dragging trawling nets than by logging.

Definition: a ribbon of seafloor that stretches from
the shore into the sea
Found: around the edges of Earth's continents
Habitats: stretches of mud, undersea canyons, and rocks
Conditions: rich in nutrients and sunlight
Depth: from 300 to 650 feet, down to where the continental slope begins

Image credits: Sean Murtha.