Earth & Sky

Ballast Water

DB: This is Earth and Sky. The three biggest threats to Earth’s oceans are probably pollution, from land – overfishing – and coastal habitat destruction by human activities.

JB: A fourth threat is carried in the ballast water of cargo ships. Cruise ships, tankers, and freighters take in and release thousands of tons of water, to maintain balance as they load and unload cargo. For the past 100 years, sea life has been traveling with ships’ ballast water from one port to another.

DB: In 1903, plankton from the Pacific, found in the North Sea, became the first organism known to be spread by ballast water. But it’s only been in the last 30 years that scientists have realized the seriousness of the threat. A foreign species in a new habitat can thrive, multiply – and overwhelm native ocean life. That’s true of zebra mussels, for example – harmless in their native Europe – very destructive in North America’s Great Lakes.

JB: And the smallest creatures might be the biggest danger. Billions of microorganisms can ride in a ship’s ballast water. Scientists worry that ballast water might carry diseases between ports. Last February, a United Nations agency adopted a convention requiring ships to treat their ballast water or release it in the open seas where, hopefully, shoreline species can’t survive.

DB: Thanks today to the National Oceanic and Atmospheric Administration and to the National Fish and Wildlife Foundation. We’re Block and Byrd for Earth and Sky.