Marine Bioinvasions: The Biologist’s Eyes

In the morning light of August 9th, 2014, Dr. Jim Carlton stands at the edge of the Mystic estuary, periodically conversing with a scuba diver who is in the water by the Morgan’s hull. The atmosphere has settled since the ship’s celebrated return to the Mystic Seaport three days ago, and Jim completes his project in the company of only his Williams-Mystic students and the occasional museum visitor. As a former director and professor of the Williams-Mystic Maritime Studies program, he is quite familiar with the Charles W. Morgan as a piece of living history. Through the 38th voyage, he also saw a window into the biological past.

Jim Carlton is a well-known expert on global marine bioinvasions. Bioinvasions occur when an invasive (non-native) species is introduced to an ecosystem, most often through human vectors. These species can become the dominant organism in many communities, replacing and displacing native species. In this way, bioinvasions can not only limit biodiversity, but they can also affect the economy in areas that contain local industries built on local species.

Jim Carlton examines natural fouling on the hull of a ship in 2008. Source: Jim Carlton

For centuries, ships and boats have distributed hundreds of organisms throughout the world’s oceans. Some attach themselves to the hulls of these vessels and often cause damage, a process known as biofouling. Others are contained in ballast water, which is carried in ballast tanks to improve the stability of the ship. When ships gather ballast water in one port, the plants and animals in that area can also be picked up. Those species are then discharged along with the ballast water when the ship reaches the next port.

Though it has taken place since the dawn of ship transportation, dispersal of plants and animals by vessels in earlier centuries is largely undocumented. Modern ships provide a difficult comparison due to the attributes of twenty-first century vessels. Less time spent in port limits the number of species that a ship can accumulate, and the ships themselves are often covered in antifouling paint to prevent organisms from attaching themselves to the hull. Because modern ships don’t behave like the Morgan, Jim viewed the 38th voyage as a unique opportunity to examine the long-term relationship between maritime history and marine biology. Using the ship as an example of a historic vector of transportation, the goal of his project was to see what kind of organisms are now moving around New England waters.

Six of the twelve fouling panels attached to the hull of the Morgan. Source: Jim Carlton

In the summer of 2013, a year before the Morgan sailed, Jim and his students placed twelve fouling panels on her hull, six on each side. In 2014, just prior to the 38th voyage, six of the twelve were removed and examined in order to provide a sample of the species had accumulated just in the Mystic estuary. These were replaced with new panels that would collect fauna as the Morgan traveled to different ports. Now, 54 days after her initial departure, a diver removes all twelve panels to see which organisms the ship brought with her. Once finished, Jim takes the panels back to his lab, where he and the students categorize what they find. Some of the barnacles that had attached themselves to the Morgan before her voyage returned alive, having grown over their long coastal tour. In addition, the Morgan picked up a variety of fouling fauna that impresses even Jim. Among these species is an invasive invertebrate known as a sea squirt that hailed originally from Japan. This organism colonized every panel along the route and was in the process of literally smothering native barnacles when it was observed.

A fouling panel removed after the 38th voyage, containing two invasive Japanese species of sea squirt as well as native barnacles accumulated in the Mystic River.

Transportation by sea remains one of the largest sources of marine bioinvasions. In the United States alone, fifty-three percent of goods are imported on marine vessels – the largest share of any mode of transportation. In addition to foreign and domestic imports, Jim predicts that there may be up to 10,000 species transported via thousands of ships on any given day. As a result, ballast water discharges have become the leading source of marine bioinvasions in coastal waters. Historically, ships traveling from the open ocean entered freshwater harbors under the assumption that any invasive species accumulated at sea would not survive the change in salinity. Unfortunately, invasive organisms adapted remarkably well as they were transported from port to port. The United States government now requires deep water ballast water releases in order to reduce the likelihood of bioinvasion in coastal ecosystems.

Though scientific research and environmental policies are beginning to address this threat, much of the responsibility for controlling bioinvasions rests in the hands of ordinary citizens. From students on a field-trip to the daily dog-walker, we are often among the first to notice new invasions in our daily environments. While the whalers are considered among the world’s first naturalists, citizen scientists have become a biologist’s eyes in this new era.