Around the world, ships moving from port to port and dumping their ballast water have often spread invasive species, including zebra mussels, toxic algae, parasites, and even cholera.
In an effort to crack down on the growing nuisance of exotic species in waterways like the Chesapeake Bay, the U.S. Coast guard in 2004 imposed a new rule for most ships entering American ports. The ships were required to dump their ballast water hundreds of miles away from shore and instead fill up their tanks with water from the open ocean. This deep water typically contains fewer coastal life forms and more salt, which can kill fresh-water creatures like invasive zebra mussels.
But when scientists at the Smithsonian Environmental Research Center in Edgewater, Maryland, studied the impact of the new regulations, they discovered something unexpected: The number of marine hitchhikers multiplied instead of decreasing.
Greg Ruiz, a marine ecologist with the Smithsonian Environmental Research Center in Edgewater, Maryland, explains why the ballast water exchange requirement should have reduced invasive species.
“It’s like the difference between a tropical forest and a desert. So the organisms like zebra mussels that are from a coastal area are dumped in the middle of the ocean have a very low chance of survivorship,” Ruiz said. “And ships are required to do the exchange 200 miles off shore. So the likelihood that a zebra mussel larvae would make it all the way to a coastal environment is incredibly low.”
But here’s what actually happened: The concentration of exotic coastal species hitchhiking into the Chesapeake in ship ballast tanks actually increased five-fold after 2005, when ballast water exchange became mandatory.
Why?
Part of the problem was increased exports of Appalachian coal through the Chesapeake Bay to Europe and China. More giant coal ships entering the bay to pick up the fuel meant nearly five times more foreign ballast water to deal with. And even under the best conditions, the ocean water exchange only eliminates some – but not all – of stowaway critters.
“Chesapeake Bay is one of North America’s major coal exporting bays – through the ports of Baltimore and also Newport News, in Virginia,” said Jenny Carney, the lead researcher on a Smithsonian study of the problem. “And these ports have seen a massive increase in the amount of coal that they have exported over the last 10 years,” Carney said. “The peak was in 2012-2013, which coincided with our sampling.”
Ironically, this was at a time when the U.S. was burning less coal – and environmentalists were applauding America’s reduced greenhouse gas emissions and the Obama administration’s restrictions on power plants that burn coal. But meanwhile, demand for American coal was quietly rising overseas. So the coal was still being mined and burned. It was just out of sight, out of mind.
“Though we weren’t burning it so much here,” said Ruiz. “We were exporting it to other markets.”
So more coal exports explain the increased volume of ballast water entering the bay. But why the increased concentration of stow-away critters after the regulations were imposed? One theory is that allowing ocean water into the ballast tanks of ships may have had the unintended effect of adding more oxygen to the water, and thus refreshing the critters and allowing more to survive the ocean journeys, instead of suffocating.
Looking to the future, still more huge international ships will soon be entering the Chesapeake Bay, as a liquid natural gas export terminal is scheduled to open at Cove Point Southern Maryland.
The good news is that U.S. Coast Guard later this year will be imposing new and stronger regulations that will set limits on the amount of floating life forms (plankton, including exotic species) per liter of water allowed in ballast tanks.
This new numeric limit should have the effect of pushing ship owners to install technologies like filters, chlorination systems and ultra-violent lights to kill sneaky and tenacious stowaways.
