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Annual Public Lectures Series > James T. Carlton

Scientists and Journalists:
Getting the Point Across
June 12-16, 2006

Biological Invasions in the Sea: Science, History and Policy
James T. Carlton, Professor of Marine Sciences, Williams College; Director, Williams-Mystic
Summary of comments from June 12

Although organisms have traveled around the globe for billions of years, humans have largely facilitated a vast increase in the speed and multitude of these migrations in modern times. James T. Carlton, Professor of Marine Sciences at Williams Colleges and Director of Williams-Mystic, presented the current state of modern biological invasions in his lecture on June 12, 2006, at the University of Rhode Island's Graduate School of Oceanography.

Carlton explained that along the New England coast and extending as far south as New York and New Jersey, the most common snail, Littorina littorea, is not an indigenous species. The snail is believed to have traveled down from Canada after being transported from Europe in the 1860s. Only 20 years after its introduction, this snail moved all the way down to the New Jersey coast and is now the most dominant snail in the area.

This is not, by any means, an uncommon scenario. Along the New England coast alone there are about 100 non-native species that have completely altered the shoreline. The Asian Shore Crab was detected about a decade ago off Long Island Sound and is now the only abundant crab in the area. One of the most remarkable aspects of this invasion, like many, is the species' ability to expand its range of possible habitats. Whereas in Japan, the Asian Shore Crab is found only in specific places, in New England the same species has managed to survive in many different settings.

San Francisco Bay is home to a multitude of invasive species, including the mud snail, which has displaced all native snails in the area. The Chinese Mitten Crab has also invaded the San Francisco Bay, necessitating the development of special machinery at water pumping stations along the Californian coast that attempt to prevent further spreading of the species. The machinery has largely slowed the spread of the Chinese Mitten Crab, according to Carlton, but has not completely inhibited it.

The invasion of the New Zealand pill bug in San Francisco Bay has brought about up to three feet of land erosion per year. With warming of temperatures along the coastline, it will undoubtedly move north with time, allowing for continued erosion of the shoreline.

After reviewing several other invaders, Carlton stated that it would be very difficult to travel around the coast of North America today without seeing the results of a significant biological invasion.

Carlton pointed out three ways in which to change the natural state of the coast: alter what is already present, remove species, or add species. The most common and most significant changes have come by way of "human mediated vectors." Ancient voyages, expansion of global exploration, colonization, and other major human migrations such as war or gold rushes, have all played major roles in the introduction of new species to an area. Cultivation of sea species for human consumption, such as edible clams, has also rapidly moved organisms around the world.

Organisms attach themselves to the outside of ocean going vessels and can live inside ships in ballast sand, rocks, and water, all of which are used to stabilize a ship that has empty cargo holds. When ballast water is released into various ports to make room for cargo, the traveling organisms are introduced to these new places. About 5,000 to 7,000 species move around the world at any given moment in the ballast water of ocean going ships.

The increase in human travel, along with other technological advances, has doubled the number of factors responsible for the movement of species and growth of invasions in the last 100 years. In the Gulf of Maine in the course of one day, there are at least 18 different agents with the potential to bring in and take out organisms, including ship ballast, sea buoys, fishing vessel nets, and private citizen release, such as fishing bait and personal sea plant cultivation.

There are serious obstacles for marine scientists to overcome in making any attempt to monitor potential carriers of invasive species. Perhaps the most notable obstacle is the number of places in which organisms can travel and survive. Shipments of seafood, marsh plants, and research or experiment equipment often carry with them additional species. Carlton recounted an incident in which he ordered one specific type of sea squirt for an educational experiment and was actually sent dozens without the shipper's knowledge.

There are four stages a species must complete to increase its likelihood of survival in a new area: uptake, transport, arrival, and post-arrival. The amount of time ships stay in port has a considerable affect on the probability of these stages being completed by any particular species. Disasters, cargo and vessel issues, and cultural events mean that a ship may stay in port for an extended period of time, increasing the chances of a new species adapting to that new place or attaching to a boat and traveling to another destination.

While there are several variables that cannot be easily monitored or regulated, there are many more that can be. Carlton expressed that it is critical to take steps in the near future in order to prevent the increased migration of invasive species and to protect organisms in their natural environments.

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December 4, 2007