Ballast Water and Alien Species

A less direct but perhaps even more insidious export of waste occurs when ships pump their ballast water in the ports where they take on cargo. Ballast water is carried in ships to add weight and thus stability to cargo vessels and other large ships when they are not carrying loads in their holds. When such vessels reach destinations where they take on cargo or supplies, the ballast water is conveniently pumped out at sea and forgotten. In and of itself ballast water is largely innocuous - besides rust residue or a small amount of fuel, the water itself is not the problem. But when ballast water is pumped into a vessel at a port of origin, many eggs, larvae, and adult plants and animals go with it. When these organisms are pumped out at ports far away, they often find themselves in places without natural predators, and can outcompete local flora and fauna to wreak ecological havoc.

The stories of invasive marine species being transported and then released under shipping operations are fascinating and bizarre. Witness the saga of the zebra mussel, which invaded the U.S. Great Lakes and major rivers as a result of being borne in ballast water from the Black Sea region. The well-documented costs of the zebra mussel invasion borders on ecologic and economic disaster. In return for that favor, subsequent ballast water originating in the western Atlantic inadvertently brought the dreaded Mnemiopsis leidyi ctenophore to the Black Sea, where the jelly-bodied creature devoured the young of most commercially important fish species and caused the ecosystem to crash. This introduction occurred through ship ballast water sometime in the 1980s, and the voracious predator eagerly preyed on the struggling biota, causing the loss of over two dozen major fisheries in a short span of years⁷. Recently, the anoxic layer of this basin has expanded and moved upwards, making restoration of the sea to its once vibrant state difficult.

Dreissena polymorpha

Mnemiopsis leidyi

Ballast-borne alien species invasions have thus reshuffled many more of the world's marine ecosystems, and caused amazing ecological and economic damage in some places⁸.

Thanks in large part to port development, estuarine systems are among the most invaded ecosystems in the world, with exotic introduced species causing major ecological changes⁹. Often introduced organisms change the structure of coastal habitat by physically displacing native vegetation¹⁰. For example, San Francisco Bay (US), has over 210 invasive species, with one new species established every 14 weeks between 1961 and 1995¹¹. Most of these bioinvaders were borne by ballast water of large ships or occur as a result of fishing activities. The ecological consequences of the invasions include habitat loss and alteration, altered water flow and food webs, the creation of novel and unnatural habitats subsequently colonized by other exotic species, abnormally effective filtration of the water column, hybridization with native species, highly destructive predators, and introductions of pathogens and disease¹².

Port development also sets the stage for alien species invasions, not through operation of the port itself but rather by port construction. Altering soft bottom habitat to hard bottom in the process often creates new assemblages of species, and facilitates range expansions of invasive species¹³. The resulting ecosystems may have losses in some ecosystem services, such as biodiversity. In New Zealand invasive species have displaced commercially important mussel beds, resulting in significant economic losses for many mussel farmers.

There have been attempts to control this problem, or at least dampen the effects of releases of competitively superior non-native species into coastal waters. New international agreements on the pumping of ballast water in commercial vessels have required ships to move at least 200 nautical miles away from land when discarding ballast water and its hitchhiking invaders – offshore, chances are less that the invasive species will gain a foothold¹⁴. Individual countries have also adopted ballast water regulations: Canada, for instance, has a ballast water management act to attempt to mitigate the problem¹⁵. In the U.S., the Coast Guard has established regulations and guidelines in order to comply with the National Invasive Species Act of 1996; however, the Environmental Protection Agency issued a regulation exempting ballast water discharges from the Clean Water Act. Legal findings in 2005 and 2006 found that such an exemption was plainly contrary to congressional intent, and the courts have ordered EPA to take specific action by September 2008 to ensure that shipping companies comply with the Clean Water Act and restrict the discharge of invasive species in ballast water¹⁶.

Nonetheless, the spread of alien and invasive species continues almost unabated, as the number of ships on the sea continues to rise. And we now know that once alien species are released and take hold on ecological communities, trying to control their spread is an exceedingly costly, and mostly futile, exercise.

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⁷ Zaitsev, Y. and V. Mamaev. 1997. Biological Diversity in the Black Sea. A Study of Change and Decline. United Nations Publications, New York, NY (USA), 208 pp
⁸ This statement and the bulk of the two paragraphs that follow it are from Millennium Ecosystem Assessment. 2005. Vol 1 Current state and trends. Coastal Systems. Pp513-549 In Ecosystems and Human Well-Bring. Island Press, Washington, DC
⁹ Carlton, J.T., 1989: Man's role in changing the face of the oceans: biological invasions and implications for conservation of near-shore marine environments. Conservation Biology, 3, 265-273.
Carlton, J.T., 1996: Marine Bioinvasions: The alteration of marine ecosystems by nonindigenous species. Oceanography, 9(1), 36-43.
¹⁰ Grosholz, E., 2002: Ecological and evolutionary consequences of coastal invasions. Trends in Ecology & Evolution, 17(1), 22-27.
Harris, L.G. and M.C. Tyrrell, 2001: Changing community states in the Gulf of Maine: synergism between invaders, oversfishing and climate change. Biological Invasions, 3, 9-21
Murray, S.N., J.A. Zertuche-Gonzalez, and L. Fernandez, in review: Invasive seaweeds: Status of knowledge and economic policy considerations for the Pacific Coast of North America. Center for Environmental Cooperation, Montreal (Canada)
¹¹ Cohen, A.N. and J.T. Carlton, 1998: Accelerating invasion rate in a highly invaded estuary. Science, 279(5350), 555-558
¹² Bax, N., A. Williamson, M. Aguero, E. Gonzalez, and W. Geeves, 2003: Marine invasive alien species: a threat to global biodiversity. Marine Policy, 27(4), 313-323.
Ruiz, G.M., J.T. Carlton, E.D. Grosholz, and A.H. Hines, 1997: Global invasions of marine and estuarine habitats by non-indigenous species: Mechanisms, extent, and consequences. American Zoologist, 37(6), 621-632.
¹³ Ruiz, G.M. and J.A. Crooks, 2001: Biological invasions of marine ecosystems: patterns, effects, and management. In: Waters in Peril, L. Bendell-Yound and P. Gallagher (eds.), Kluwer Academic Publications, Dordrecht (Netherlands), 1-17.
¹⁴ The International Maritime Organization’s agreement on Ballast Water Management has 10 contracting parties as of May 31, 2007; 30 are needed to have the treaty enter into force. See www.imo.org/conventions/mainframe.asp?topic_id=247
¹⁵ See www.tc.gc.ca/acts-regulations/GENERAL/C/csa/regulations/400/csa448.html
¹⁶ enewsusa.blogspot.com/2006/09/court-orders-epa-to-develop-ballast.html