When it comes to invasives, who to turn to?

A profile of James Carlton

By Lori Valigra

WHEN JAMES CARLTON was 14 years old, he discovered a clump of worm tubes on the beach of Lake Merritt near his home in San Francisco Bay. He was so fascinated by the worms, which he later learned were native to the South Seas, that he spent years surveying the entire lake for plant and animal life. And he made invasive species his life's work.

Now, more than four decades later, Carlton is a renowned marine ecologist and evolutionary biogeographer (the study of how species get to where they are located) who directs his keen eyes toward invasive species in local waters. He also watches for something that is perhaps more difficult to detect: the extinction of species. Carlton has been on the faculty of Williams College in Williamstown, Massachusetts, since 1989, and serves as director of a 20-college Maritime Studies Program at Williams College-Mystic Seaport in Mystic, Connecticut.

“When I found the worms as a teenager I wasn't sure what they were, so I went to the local nature center and saw a display about them,” he said. “It was fascinating how something in Oakland came from the South Seas.” Naturally curious, Carlton talked to historians and to a zoology professor at the California Academy of Sciences in San Francisco who he said helped him a lot. Unlike many teens, he also read historical scientific literature to find out more about marine invasions, which in San Francisco Bay dated from the active shipping at the time of the Gold Rush.

The human hand in marine invasions

As an undergraduate at the University of California at Berkeley in the 1960s, Carlton first studied linguistics, but then turned his mind toward paleontology, in which he received his bachelor's degree. He went on to study exotic species invasions from Alaska to Baja, California at the University of California at Davis, where he earned a Ph.D. in ecology. He did postdoctoral work at the Woods Hole Oceanographic Institution in Massachusetts, where he had planned to study marine invasions from Canada to Florida, but found the task “daunting.”

“I thought it would be easier to do this kind of study on the East Coast because it [information on marine species on that coast] has been known for a longer time,” he said. “But the signature of human activity also is older, dating back to the 1500s when ships explored the Atlantic Coast. West Coast activity dates only to the 1800s.” The field of marine biology didn't evolve until the mid-1800s. Scientists typically relate alien species invasions to the human impact that helped cause them.

While marine organisms have traveled around the globe for millions or even billions of years, humans have greatly increased both the speed and quantity of marine migrations in modern times. Ancient voyagers, colonizers, global explorers and today's international shippers and travelers have played major roles in introducing new species to new areas. Marine organisms can live in the ballast water used to stabilize a partly empty cargo vessel. That water is then discharged in foreign ports to make room for new cargo. There are thought to be about 5,000 to 7,000 species in the ballast water of the 40,000 ships moving around the world at any given moment. In addition, organisms attach to the outside of ocean vessels, and they are inside seaweed and other packing for shipping seafood for human consumption via Federal Express and other fast shipping methods.

“What really changed the face of the Earth is the global signature of humans moving species from Hong Kong to San Francisco Bay or the United Kingdom to Australia,” Carlton said. “An extraordinary number of species have been moved between continents. Movement by birds or the wind takes much longer.”

Even though only a small percentage of the alien species survive their travels and become invasive, still too many become what Carlton calls “kick butt” invasive. And they can do so in small vectors (the means by which they travel). One example is the bait worms from Maine that are wrapped in seaweed and shipped to the West Coast. The seaweed also contained green crabs, which subsequently invaded the West Coast. “Minor vectors (such as seaweed packaging) still can lead to huge invasions,” Carlton added.

In the Gulf of Maine there are at lease 18 different agents that can bring in and take out organisms each day including ship ballast, buoys, fishing nets, and private citizen release including personal sea plant cultivation.

Web-based invasions

Determining the damage done by invasions is tricky. “If a species has been here 500 years does it matter that it is 'naturalized' here?” Carlton asked. “To what or whom is a species harmful? In Prince Edward Island in Canada, the club tunicate (a sea squirt) had a massive impact on mussel aquaculture.” He said the damage toll of invasives typically is made when political or economic factors are attached, such as an invading species damaging a rich fishery or the outbreak of zebra mussels in the Great Lakes blocking water flow to homes.

There are enough invasive species around that people should be worried, said Carlton. Only recently, a fisherman in Nahant, Massachusetts, found a large Dungeness crab native to the Pacific Northwest, including Oregon. And at a recent meeting of the U.S. Environmental Protection Agency (EPA), Carlton said talk focused on perhaps the most ubiquitous vector yet for invasions: the World Wide Web. “A lot more living organisms are brought to your door than before,” said Carlton. “There's a live seafood industry, and everything is getting moved around. Packages marked 'for human consumption' get across almost every border in the world.” He said the EPA is trying to get a handle on what types of organisms are being shipped via the Web, but right now, the sheer volume overwhelms customs and agriculture agents.

“The ability to move species faster and greater distances has increased dramatically and continues to increase,” he said. “But I am optimistic. We are now living in a time when there's never been so much research into the subject. Going forward the challenge will be how we get a handle on bioflow.” A new phrase in the field is “early detection, rapid response,” meaning that if it is possible to localize the first invasion, it may be eradicated. Citizen groups and beachgoers including runners, birdwatchers, kayakers and fishermen have been helpful in reporting invasions. “Closing the barn door is always useful,” Carlton said.

An invasive algae from the Mediterranean known as Caulerpa taxifolia was recently eradicated from two locations in Southern California. It already is so pervasive in the Mediterranean that it likely cannot be exterminated: one patch that was a yard long in 1984 now covers an estimated 30,000 acres of sea floor. It was discovered in California in 2000, and Carlton said it hadn't been seen for about two years before the eradication announcement was made. But the eradications are the exception rather than the rule. “The Asian short crab is too widespread to eradicate,” said Carlton of the New England invader. “It would be easier to take a picture on Mars than to do this.”

When species go missing and no one notices

Partially because so many new species are being introduced, it is more difficult to tell when a species “goes missing.” “We see a lot of invasions, but who knows how many species of whale have gone extinct at the hands of many in the last 500 years?” said Carlton. “Not much has been studied about extinctions.” Some extinctions in the Gulf of Maine include the Maine coast sea mink, which was hunted to extinction in the 1880s. Another is the great auk, which grew to about three feet high, also hunted to extinction in the Gulf of Maine in the 1700s.

And then there's the eelgrass limpet, a snail made extinct by the eelgrass blight. “Even though it was last collected in 1929, seashell books still say there are eelgrass limpets,” said Carlton. “Why do species go missing and no one notices?” Carlton said. In some cases, species are in such a decline that they are “functionally extinct.” They no longer play a role in their environment, such as the Blanding's turtle and some fish, he added.

Carlton hopes to spend more time in the future investigating extinctions. He soon will finish a book on invasive species in Hawaii. Carlton has spent about 15 years going to Washington to testify before Congress or talk to federal agencies about invasive species. “I would like to encourage the public to come forward when they see something,” said Carlton. “The crab off Nahant was reported to a biology professor at Salem State College. We are waiting for the next zebra mussel. And we want to prevent the ghost of Christmas future.”

Carlton also was a 1996 Pew Fellow in the Environment and Conservation and is the founding Editor-in-Chief of the international “Biological Invasions.”

© 2006 The Gulf of Maine Times