Campus News

For invasive species, it’s better to start upstream

Researchers have found that a species invasion that starts at the upstream edge of its range may have a major advantage over downstream competitors, at least in environments with a strong prevailing direction of water or wind currents.

Scientists from UGA,  the University of New Hampshire, the Smithsonian Environmental Research Center and the University of Vermont studied populations of European green crab, Carcinus maenas.

The species was introduced to the East Coast of North America twice, at both the upper and lower edges of its range. Their findings, recently published in the Proceedings of the National Academy of Sciences, may help inform the control of invasive species and the conservation of imperiled native species.

The European green crab was first detected in North America in New Jersey in the early 1800s. It spread slowly north against the prevailing direction of ocean currents until it reached Halifax, Nova Scotia, in 1964. That was the extent of its range along the East Coast until the 1990s, when populations suddenly appeared throughout the Canadian Maritime provinces.

These new crab populations were genetically different from those established earlier­—suggesting a new introduction directly from Europe to Nova Scotia had taken place. And understanding how the species spread could offer insights into how to control it.

The second crab invasion was established in the Strait of Canso and Bras d’Or Lake in northern Nova Scotia, locations well suited to serve as large population retention zones.

Researchers genetically sampled crab populations from New York to northern Nova Scotia from 1999 to 2007. They found that the northern crabs were making up a greater share of the crab population at each sampling site as time progressed.

The team also found that areas not previously invaded by southern crabs were susceptible to invasion by northern crabs.  The currents were carrying the crab larvae downstream into areas that southern crabs weren’t able to colonize, said Jeb Byers, an associate professor at the Odum School of Ecology and one of the paper’s authors.

The team’s findings could help target efforts to control invasive species and conserve native species in environments influenced by water or air currents.