62 Life in the Current-Mid

Life in the Current FOCUS Question How does the East Australian Current support living things?

Rivers in the Ocean In the movies, a young fish may hitch a ride with a sea turtle and ride a current to zip through the ocean. Ocean currents are like huge rivers flowing within a larger body of water. They move in regular patterns around the ocean. Currents at the surface are caused by wind and by Earth's rotation. Real animals ride on ocean currents including on the "movie star" known as the East Australian Current (EAC).

Speedway of the South Pacific The EAC is a lot like a current in the Atlantic Ocean called the Gulf Stream (see map on page 2). Both currents are fast-flowing and bring warm, tropical water to cooler water regions. The EAC zips through the Pacific Ocean at up to 177 kilometers (110 mi.) per day. This current flows near the ocean's surface. It begins in the warm, tropical Coral Sea. From there, it sweeps south along the east coast of Australia. It ends in the Tasman Sea, where it mixes with the sea's cooler waters. Both the Gulf Stream and the EAC are part of complete circles of ocean currents called gyres (see map on page 2). As these strong currents flow, swirling loops of water called eddies break off from the main current. Math Moment The Gulf Stream moves at speeds of up to 216 kilometers (134 mi.) per day Which current is faster, the EAC or the Gulf Stream? How much faster?

Come Up for a Meal Where eddies form, the ocean comes alive! When an eddy breaks off from the main current, it drifts into cooler water. As the warm eddy swirls, cold water from deeper in the ocean is pulled up in a process called upwelling. Deep, cold water is rich with nutrients, minerals, and other living things. Cold water, holds more oxygen than warm water, and since organisms need oxygen, they are plentiful in areas with cold water. As a result, the number of living things is higher in areas of upwelling. Up at the surface, these living things provide abundant food for fish and other ocean creatures of the EAC.

Catch a Ride The EAC is fastest and strongest in spring and summer. That's when its powerful flow sweeps up thousands of living things. They leave their homes in the warm Coral Sea to catch a ride on the current and head south to the cooler waters off Australia's southeast coast. These northern "tourists" include colorful reef butterfly fish. They also include humpback whales, eastern rock lobsters, and tiny plankton. Some fish and other ocean organisms, such as lobsters and sea stars, use the EAC to spread their larvae far down the coast. The babies find new habitats where they can grow up.

Go with the Flow Sea turtles also ride the EAC— and not just in the movies! Baby loggerhead turtles hatch from eggs laid on beaches in northeastern Australia. While still tiny, they crawl into the sea and ride the EAC south. Soon the current swings east, away from the coast, and joins the South Pacific Gyre. The tiny turtles go with the flow. Caught in the current, the turtles shoot across the vast Pacific toward South America. As they become adults, they circle back to Australia by riding other currents in the South Pacific Gyre. There, they hit the beach again to nest and lay eggs of their own.