At any one time, more than 3,000 species are being transported around the world in the ballast water of large ships. Each hour, an average of 2.5 million gallons of foreign water is being poured into U.S. waters from foreign ships.
Those calculations were made by James T. Carlton, of Williams College in Connecticut, who refers to ballast water transport as a giant "biological conveyor belt" that is responsible for a "flood of irreversible global invasions."
"What nature took millions of years to create - distinctly separate biotas of different species around the world - human activities are homogenizing in tens of years through transport mechanisms that instantaneously transcend the natural barriers of open oceans and continents," Carlton said in his keynote address to a 1993 conference on nonindigenous estuarine and marine organisms that was sponsored by the National Oceanic and Atmospheric Administration.
Unlike organisms of the past - which had to cling to the outside of slow moving ships and were exposed to a variety of conditions such as fluctuating salinity levels - organisms today are hauled inside fast-moving ships. And ballast water conditions inside are more uniform than those in the open sea, making trip survival more likely.
Carlton was one of the first researchers to focus on risks associated with ballast water transport. A study he conducted of 159 ships entering Coos Bay, Oregon, during the early 1990s found 367 species of living animals and plants in ballast water. And that study focused on only one shipping route - from Japan to the Pacific Northwest.
Given the enormous amounts of ballast water being transported around the world, Carlton believes many areas are being affected by nonnative species but have not been studied.
Nonetheless, some of the known invasions have had great impacts. Some cited by Carlton include:
- A voracious plankton-eating comb jelly, Mnemiopsis leidyi, native to the Atlantic Coast was transported to the Black and Azov seas in the early 1980s. Its uncontrolled growth because of the lack of predators has led to a vast decrease in zooplankton and the near-extinction of local anchovy fisheries, costing the Black Sea fisheries $250 million a year, and closing the once-productive Sea of Azov fisheries.
- The Japanese crab Hemigrapsus sanguineus was detected in New Jersey in 1988 and is expected to move south to Chesapeake Bay and North to Cape Cod. It arrived as larvae or juveniles in ballast water. It is a small, rocky shore crab which may compete with similar small crabs under midtidal rocks for food and space, although it is unlikely to have the scale of impact of the American comb jelly in the Azov Sea.
- The Japanese kelp Undaria pinnatifida and the Japanese seastar Asteria amurensis have appeared in southeastern Australian and Tasmanian waters, where they are proceeding to, respectively, occupy extensive space and consume native shellfish (such as abalones). Both are believed to be ballast water introductions.
- The North American razor clam Ensis directus was discovered in Germany in 1979, having been carried to Europe as larvae in ballast water. It has spread to Denmark, Belgium, the Netherlands and France, and it is becoming one of the most common local species.
There have been distinct global increases in "red tides" (toxic phytoplankton blooms, or harmful algal blooms) in the past 20 years. Australian studies have demonstrated the actual and potential role of ballast sediments in transporting the cysts of bloom-causing dinoflagellates. It appears now that many of these blooms are caused by species introduced by ballast water and sediments.
Once they arrive, Carlton said the outlook for dealing with invading organisms is bleak.
"No introduced marine organism, once established, has ever been successfully removed or contained, or the spread successfully slowed," he said. "At the moment, the invaders seem to be coming thick and fast across our bow. But we are now aware more than ever before, and with this awareness comes great hope for the development of specific and enforceable controls that will limit further accidental alterations to the world's freshwater and marine environments."
Copies of the proceedings of from the Conference and Workshop on Nonindigenous Estuarine and Marine Organisms, which was held in Seattle, Wash., on April 20-22, 1993, are available from the National Atmospheric and Oceanic Administration's Office of the Chief Scientist. Contact Commander Herb Kirch, (202) 482-5181.