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Image left: SERC scientist João Canning Clode observes a green porcelain crab in his laboratory at the Smithsonian Environmental Research Center.

But what happens to these fair-weather travelers during a severe cold snap, such as the one that occurred in January 2010 across much of the southeastern and eastern United States? To investigate, Smithsonian Environmental Research Center scientist João Canning Clode and colleagues at the Environmental Research Center in Edgewater, Md., tested the cold-water tolerances of invasive green porcelain crabs (Petrolisthes armatus) in their laboratory. Crabs were collected in Georgia and brought to the lab where they were subjected to one of three temperature treatments. The first was a control treatment of constant moderate winter temperature. The second was treatment in which the temperature was dropped to mimic the cold snap of January 2010, and the third treatment consisted of the extreme cold temperatures of a severe winter.

Canning-Clode and his colleagues found that most of the crabs in the control treatment survived (83%), but many of the crabs in the second cold treatment (61%) and all of the crabs in the third extreme cold treatment (100%) died. Crabs that survived cold treatment number two were sluggish, possibly making them more susceptible to predation and impacting their ability to feed, the scientists determined.

The scientists determined that prolonged exposure to cold temperatures also may compromise the green porcelain crab’s ability to overcome cumulative cold events, such as the two other record cold snaps that occurred in February and March of 2010.

Image right: A green porcelain crab (Photo by Juan Antonio Baeza)

The loss of more than 60% of their population during each cold period might explain the recent dramatic decline of the green porcelain crab in Georgia in 2010, suggesting that extreme cold spells may limit or prevent the northward spread of this invasive species.

Several climate models used to predict how species will react to climate change in the next 100 years have projected a continued decline of global biodiversity and increased spread of introduced species. Many of these models focus on temperature increases, but few have evaluated the impact of severe weather like cold snaps, Canning-Clode and his colleagues write in a paper on their study recently published at PLoS ONE.

For Canning Clode “the core message of this paper is that yes, climate change is happening, but cold is also part of this change. We believe these periodic cold events will limit the range expansion of Petrolisthes armatus as well as other Caribbean creep species” –Monaca Noble, SERC

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Image left: Coyote (Rebecca Richardson)

According to the study, coyotes migrated eastward via two main routes—one that went through the northern United States, and one that went through the south. Using DNA samples, the researchers found that Virginian coyotes were most closely related to coyote populations in western New York and Pennsylvania. It appears the northern trekkers eventually encountered the Great Lakes wolves and interbred before converging again on the East Coast. They then gradually headed south along the Appalachian Mountains toward what is considered the Mid-Atlantic region, to an area centered around Virginia.

“The Mid-Atlantic region is a particularly interesting place because it appears to mark a convergence in northern and southern waves of coyote expansion,” said Christine Bozarth, an SCBI research fellow and lead author on the paper. “I like to call it the Mid-Atlantic melting pot.”

Bozarth and her colleagues collected scat samples in Northern Virginia from local coyote populations. They were then able to extract DNA from the intestinal cells in the scat and compare it to the DNA from preserved historic wolf specimens that had lived in the Great Lakes region before coyotes colonized the area. They shared some of the same genes, supporting the hybridization theory. Hybridization between canid species usually occurs when one species is rare. Those individuals may have trouble finding mates and therefore breed instead with closely related species.

“This does not mean that we have massive, wolf-like coyotes roaming around here in Virginia,” Bozarth said. “Coyotes with wolf ancestry have differently shaped jaws, which may allow them to fill different ecological niches. They tend to hunt small prey and scavenge large game, so hybrid coyotes might be helpful in controlling the overly abundant deer population.”

Image right: Camera trap photo of a coyote taken Feb. 15, 2008 at Quantico Marine Base in Virginia. (Courtesy of Quantico Fish and Wildlife Office)

While coyote populations have been expanding, wolf populations have become endangered. Hybridization with coyotes is now a major threat to the recovery of wolves.

“For the past decade, our lab has developed and used noninvasive techniques to monitor and survey rare and endangered species in various regions of the world and in this study, we were able to show that noninvasive techniques can also be an effective tool for tracking the origins and movement patterns of this elusive canid,” Jesús Maldonado, SCBI research geneticist and paper co-author. “The admixed coyotes have also been found further south, into North Carolina, which brings the hybridized coyote into the range of the critically endangered red wolf, further complicating the issue.”

The study’s authors from SCBI are Bozarth, Maldonado and Frank Hailer (now a postdoctoral researcher at the Biodiversity and Climate Research Center in Frankfurt, Germany). Bozarth is currently an assistant professor in the science, technology and business division at Northern Virginia Community College. The additional authors are Larry Rockwood and Cody Edwards from the department of environmental science and policy at George Mason University.

The Smithsonian Conservation Biology Institute plays a key role in the Smithsonian’s global efforts to understand and conserve species and train future generations of conservationists. Headquartered in Front Royal, Va., SCBI facilitates and promotes research programs based at Front Royal, the National Zoo in Washington, D.C., and at field research stations and training sites worldwide.

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Scientists from the University of Georgia, University of New Hampshire, Smithsonian Environmental Research Center and 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.

Image right and below: Green crabs

“In New England, they’re worried,” said Jeb Byers, an associate professor at the UGA Odum School of Ecology and one of the paper’s authors. “These green crabs have been doing a number on native shellfish. They eat a lot of clams. And they’re a very cosmopolitan species—they’ve now spread all over, to places as far afield as the West Coast of the U.S. and South Africa.”

The European green crab was first detected in North America in New Jersey in the early 1800s, Byers said. 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.

Conservation biologist Joe Roman of the University of Vermont, another of the paper’s authors, determined that these new populations were genetically different from those established earlier. Analysis revealed that unlike the earlier arrivals, they were related to European green crabs found in the Baltic, suggesting a new introduction directly from Europe to Nova Scotia had taken place. Other authors of the paper include James M. Pringle of the University of New Hampshire and April M. H. Blakeslee of the Smithsonian Environmental Research Center.

Understanding how the species spread could offer insights into how to control it.

“Our theory was that the old invasion spread as far as it could upstream before fighting the currents made it impossible to spread farther,” Byers said. “We suspected that the new invaders were successful essentially because of physics. Unlike their predecessors, they didn’t have to fight their way against the current to spread. They just had to disperse their larvae into the water column and let the current carry them south along the coast.”

The second crab invasion 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. These zones anchor the crab population because they are not subject to the strong currents typical of the outer coast.

“If you look at the prevailing ocean currents in the area, you can see that these population retention zones are at the upstream edge of practically the entire distribution of the crabs,” Byers said. “Crab larvae enter the water column from there and drift south.”

Byers and his colleagues 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 northern crabs were 20 percent more common within only a few generations,” Byers said.

They 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 from the northern populations into areas that the crabs moving under their own power up from the south were unable to colonize,” he said.

The team’s findings could help target efforts to control invasive species and conserve native species in environments influenced by strong water or air currents.–Source: Odum School of Ecology, The University of Georgia

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Image right: Horn snails (Photo by Kevin Lafferty)

“Just as people use airplanes to fly overseas, marine snails may use birds to fly over land,” said Mark Torchin, staff scientist at the Smithsonian. “It just happens much less frequently. There’s also a big difference between one or two individuals ending up in a new place and a really successful invasion, in which several animals survive, reproduce and establish new populations.”

The discovery of the hitchhiking snails, published in Proceedings of the Royal Society: B, has broad implications. “Not only snails but many intertidal organisms may be able to ‘fly’ with birds,” said first author of the study, Osamu Miura, assistant professor at Japan’s Kochi University and former postdoctoral fellow at the Smithsonian Tropical Research Institute in Panama.

Chance events that occur only once in a great while may be extremely important in the history of life. In 1940, George Gaylord Simpson, who studied natural history as recorded in fossils, coined the term “sweepstakes dispersal” to describe the unlikely events in which animals cross over a barrier resulting in major consequences for the diversity of life on Earth. Simpson was thinking about land-based animals that might “get lucky” and cross between continents or islands by floating on rafts of debris. Sometimes such events result in devastating biological invasions—introducing new diseases, wiping out resident species or causing economic damage to food crops.

Image right: Osamu Miura collecting snails.  (Photo by Mark Torchin)

The idea of land snails hitching rides on birds goes back to Charles Darwin, who speculated that migratory birds could transport snails to distant places. In fact, birds are thought to have carried land snails 5,500 miles from Eur

ope to Tristan de Cunha Island in the South Atlantic Ocean and back. But this is the first report of a marine snail “flying” from one ocean to another.

Scientists working at the Smithsonian in Panama have long been interested in how the rise of the Central American land bridge more than 3 million years ago drove speciation and increased biodiversity. It formed a barrier between marine species, some of which evolved in their new surroundings, becoming new “sister” species that could no longer mate with their former relatives.

By studying the genetics of two sister species of horn snails, Cerithideopsis californica and C. pliculosa, collected at 29 different locations in mudflats and mangrove habitats from California to Panama on the Pacific and from Texas to Panama on the Atlantic, the researchers discovered that, about 750,000 years ago, these snails invaded the Atlantic from the Pacific, and then, about 72,000 years ago, Atlantic populations returned to invade Pacific shores.

“Shorebirds mostly move back and forth across Central America via a couple of flyways,” said Torchin. “We think that the snails were able to cross the Isthmus of Tehuantepec in Mexico because it’s a major bird flyway and is a relatively flat and narrow stretch of land with ideal tidal flat habitat on either side.”

“There is a chance that the hitchhiking snails benefited native populations by bringing in new genes that helped them resist common parasites that castrate the snails and keep them from reproducing,” said Ryan Hechinger, associate research biologist at the University of California, Santa Barbara. “Now we are looking at the parasite genes to see if they jumped Central America too.”

“Understanding that such hitchhiking occurs can help reveal where new species might have become established or where they might establish in the future,” said Eldredge Bermingham, STRI director and staff scientist. “I am here in Panama watching as snails fly over my head. Tongue in cheek, I fail to understand why others did not notice this before! I suspect our interpretation of this phylogeographic pattern would make George Gaylord Simpson smile.”

Reference: Osamu Miura, Mark E. Torchin, Eldredge Bermingham, David K. Jacobs, Ryan F. Hechinger. Proceedings of the Royal Society: B. (Sept. 14, 2011)

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The idea that the colder temperatures of high-latitude regions act as a natural barrier to invasive species is a misconception.

Image right: The European green crab, Carcinus maenas. (Photo by Hans Hillewaert)

“Environmental conditions along the coastline of Alaska and many other high-latitude areas would not prevent successful invasion of non-native marine species with distributions now restricted to lower latitudes,” the scientists write in a recent paper published in the conservation biogeography journal “Diversity and Distributions.”

The team, which includes Anson Hines, director of the Smithsonian Environmental Research Center; Gregory Ruiz, head of the Center’s Marine Invasions Research Lab, and Portland State University ecologist Catherine de Rivera, base their predictions on a series of niche models they created for four taxonomically diverse marine species: the European green crab (Carcinus maenas), rough periwinkle (Littorina saxatilis), bay barnacle (Amphibalanus improvisus) and the sea squirt (Styela clava).

Image left: Sea squirt, Styela clava. (Photo courtesy Fisheries and Oceans Canada)

Using a wide range of scientific data detailing where each species is presently established around the globe—both in their natural and introduced ranges—the scientists created computer models projecting where else on Earth they might logically thrive. Much of the Pacific coast of Alaska came up as a strong match for each of the species. The geographic range of all four animals received a strong nudge northward in the models when higher temperatures predicted from climate change (a rise of between 1.5 and 7 degrees Celsius) were factored in.

The scientists point out that their study focuses on only four invasive species out of more than two hundred that have become established in the region adjacent to Alaska, from California to British Columbia. If more invasive species do move north into Alaska it will likely come through an increase in the frequency and intensity of introductions, the scientists write—namely on commercial ships and recreational vessels, through aquaculture, and through the live trade of animals as food, pets and bait.

Invasive species ride in the ballast water of oil tankers and some cargo ships. Cruise ships and cargo barges can carry invasive species attached to their hulls.

Image right: The shell of the rough periwinkle, Littorina saxatilis. (Photo Amy Benson, USGS)

Alaska has been spared so far from an influx of invasive species, the scientists say, because the magnitude of shipping and other human-mediated transfer mechanisms has been historically low. In recent years however, vessel traffic has increased considerably along the Alaskan coast. For example, more than 7,000 ships arrived to Alaskan waters in 2004 alone, discharging over 4 million metric tons of ballast water. Shipping and other human activities are projected to increase in this region, especially if climate change brings warmer temperatures.

The probability of invasions in Alaska is likely to increase with global warming even without the help of ballast water introductions, the scientists conclude. “On a global scale, the suitability of Alaskan waters is not unique, as other high-latitude areas also offer environmental match for these species,” the scientists write.

“The ranges of all four species have slowly been moving northward up the coast and they may spread further up the coast by ocean currents,” Catherine de Rivera says.

The article “Potential for high-latitude marine invasions along western North America,” authored by Catherine de Rivera, SERC ecologist Brian Steves, SERC ecologist Paul Fofonoff, Anson Hines and Greg Ruiz, appeared in the journal Diversity and Distributions.

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Image left: The team of researchers and interns from the Smithsonian Enviornmental Research Center display the northern snakehead fish they recently found in the Rhode River.

Native to China, the first northern snakehead in Maryland was reported in 2002 in a Crofton pond, approximately 20 miles east of Washington, D.C. That population was eradicated, but a separate introduction occurred in the Potomac River in 2004, which led to the establishment of the northern snakehead in creeks and upper waterways of the Potomac in Maryland and Virginia.

The snakehead was caught during routine sampling at a long-term study site using a seine net. It represents the only specimen recorded for the Rhode River site in decades of such surveys. The fish was a mature female, 58 cm (23 inches) in length, caught near the headwaters of the Rhode River.

The northern snakehead is typically found in freshwater, although it can tolerate low salinity waters.  It was thought that higher salinity at the mouth of the Potomac may act as a natural barrier, serving to limit or reduce the fish’s spread to other tributaries. Due to extremely high levels of spring runoff in Upper Chesapeake Bay this year, salinities in Chesapeake tributaries are at some of their lowest levels in the last 30 years. This has potentially allowed the fish to move out of the Potomac and travel to other rivers via Chesapeake Bay.

Image right: The northern snakehead fish specimen recently found in the Rhode River.

Unlike most fish, the northern snakehead can survive up to four days out of water if kept moist. This ability comes from air chambers above their gills that act as a primitive lung. They are top-level predators with the ability to consume other fish and animals up to one-third of their own body size.  Northern snakeheads may cause declines in local fish and other organisms, causing potential changes to the food web.

The fish was caught by a research team of scientists and interns from SERC’s Marine Invasions Research Lab, which studies patterns and effects of biological invasions in coastal marine ecosystems throughout North America.  Information on this and other non-native species in Chesapeake Bay can be found at SERC’s website (http://invasions.si.edu/nemesis/chesapeake.html).

Any movement or possession of a live northern snakehead fish is a violation of state law. If you catch a Northern Snakehead, please do not release it. Anglers are asked to kill the fish and contact Maryland or Virginia Departments of Natural Resources.

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A recent study in a forest at the Smithsonian Environmental Research Center in Edgewater, Md., has shown that soon after a tree falls, wineberry seedlings pop-up in the gap created by the fallen tree. These opportunistic plants quickly fill-in the gap, taking advantage of the increased light coming through the tree canopy and the fresh soil at the fallen tree’s turned-up roots. Once established on the forest floor wineberry canes rarely die. The rapid growth of the plant is slowed after the canopy closes again. Its canes remain on the shaded forest floor waiting to spread further with the next tree fall.

Image above and left: Wineberries (Rubus phoenicolasius) (Photo above by Eva-Maria Kintzel/Photo left by Rasbak)

Native to Japan, China and Korea the wineberry or wine raspberry was introduced to the United States in 1890. It is now listed as invasive in Maryland, Pennsylvania, Tennessee, Virginia, North Carolina and West Virginia. A vigorous grower, it forms dense thickets of prickly red canes with broad leaves covering large areas and displacing native plants. In the eastern United States it is now common along forest, field, stream and wetland edges and in open woods.

During the experiment conducted by David Gorchov of Miami University ; Dennis Whigham, senior scientist at the Smithsonian Environmental Research Center, and their colleagues, the team learned that a thick layer of leaf litter is a forest’s best defense against wineberry seedlings. Bare soil, such as that found at the turned-up roots of a fallen tree, promotes the sprouting of wineberry seedlings.

The bad news, the researchers write, is “that this invasive will become pervasive even in old stands,” of deciduous forest. “The good news is that the invasion of old stands can be prevented by simple cultural control.” The scientists recommend searching new treefall gap areas in a forest every three years and pulling up any R. phoenicolasius seedlings and young plants that are found there.

A paper “Treefall gaps required for establishment, but not survival, of invasive Rubus phoenicolasius in deciduous forest, Maryland, USA,” appeared in a recent issue of the scientific journal Plant Species Biology.–John Barrat

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