EVERY minute of every day, what ecologist James Carlton calls a global ``conveyor belt'' redistributes ocean organisms. It's a planetwide biological disruption that scientists have barely begun to understand.
Dr. Carlton - an oceanographer at Williams College in Williamstown, Mass. - explains that, at any given moment, ``there are several thousand [marine] species [traveling] ... in the ballast water of ships.'' These creatures move from coastal waters where they fit into the local web of life to places where some of them could tear that web apart. This is the larger dimension of the infamous invasion of fish-destroying, pipe-clogging zebra mussels.
Such voracious invaders at least make their presence known. What concerns Carlton and his fellow marine ecologists is the lack of knowledge about the hundreds of alien invaders that quietly enter coastal waters around the world every day. Many of them probably just die out. Some benignly - or even beneficially - join the local scene. But some will make trouble.
In one sense, this is an old story. Organisms have ridden ships for centuries. They have clung to hulls and come along with cargo. What's new is the scale and speed of the migrations made possible by the massive volume of ship-ballast water - taken in to provide ship stability - continuously moving around the world.
As ecologist Greg Ruiz at the Smithsonian Institution's Environmental Research Center in Edgewater, Md., notes, ``the single largest source of alien species is the worldwide movement of ballast water.''
Ships load up with ballast water and its inhabitants in coastal waters of one port and dump the ballast in another port that may be thousands of kilometers away. A single load can run to hundreds of thousands of gallons. Some larger ships take on as much as 40 million gallons. The creatures that come along tend to be in their larval free-floating stage. When discharged in alien waters they can mature into crabs, jellyfish, slugs, and many other forms.
It will take detailed research on a global scale to learn what species are moving around and how they affect alien ecosystems. The Smithsonian's Greg Ruiz is carrying out such a program for Chesapeake Bay in collaboration with several other Smithsonian scientists and Williams College researchers. As outlined in the current issue of the institution's Research Reports, they are sampling ballast water released into Baltimore Harbor that then ends up in the bay. Dr. Ruiz says that early results show that live organisms arrive from as far away as Japan. They include crabs, shrimp, worms, clams, and algae.
Since the problem involves coastal species, simply banning ballast dumps in coastal waters would, in theory, solve it. Coastal organisms in ballast water that is flushed into midocean would not survive. Such a ban has worked for the North American Inland Waterway. But it would be hard to enforce it worldwide. Heating ballast water or straining it should also halt the species spread. But before any such worldwide regulations were imposed, scientists would need a clearer view of what is going on.
James Carlton chairs a working group of the International Council for the Exploration of the Sea that is studying this situation. Also, legislation is pending in the United States Congress that would provide $2 million for research on controlling harmful invasions from ballast dumps. These are small efforts compared to the scale of the challenge.
The continuous shuffling of marine organisms has changed the biology of the sea on a global scale. It can have devastating effects as in the case of the American comb jellyfish that recently invaded the Black Sea. It has destroyed that sea's anchovy fishery by eating anchovy eggs. It may soon spread to western and northern European waters.
The maritime nations that created the biological ``conveyor belt'' should support a coordinated international effort to find out what is going on and what should be done about it.