For decades, ecologists have assumed the worst invasive species—such as brown tree snakes and kudzu—have an “away-field advantage.” They succeed because they do better in their new territories than they do at home. A new study led by the Smithsonian Environmental Research Center reveals that this fundamental assumption is not nearly as common as people might think.
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by Monaca Noble and Paul Fofonoff
The title question was raised by one of the readers of last month’s feature story on green crabs (Carcinus maenas). The reader asked, “If the green crab was first seen here [the East Coast of the US] in 1817, is it still considered an invasive species 200 years later? How far back do you go to claim something is invasive vs. native?” Several groups of people have drawn their own lines in the sand, but we wanted to examine current thoughts and perceptions. The following article is based on views expressed in a recent listserve discussion.
The term invasive was used in the green crab article because the crab is on the list of the world’s 100 worst invasive species. But it is also commonly used as a synonym of introduced. Which brings us to the importance of terms and definitions.
As one respondent pointed out, there are different interpretations of the term “invasive.” Some people define invasive in terms of a species’ ecological impact or behavior, while others use it to refer to a species’ origin, and sometimes both are part of the definition. If a species’ characterization as invasive is based only on its ecological behavior, then it is possible for a species to be both native and invasive. But if the species’ origin is part of the definition, then only nonnative species can be invasive. Others add another dimension to the word by making the mode of introduction important. Species can be spread naturally through dispersal and/or through human-mediated transport. Some people use invasive in reference to human-mediated introductions of nonnative species. Unfortunately, when we hear the word “invasive” we rarely know the definition behind it.
But whether something is considered invasive appears to be largely a matter of perception rather than just definition, and there are many contributing factors that muddy the water. Most responses from the discussion fell into three perception categories represented by these questions:
1) Do we benefit from the species, or is it harmful?
2) Is the species part of what we consider the natural landscape?
3) Is the species native?
Maybe our problem is that we view nature in the time frame of a biologist’s career-span.”
by Monaca Noble and Linda McCann
European green crabs are eating and marching their way up the west coast.
One of nine marine invertebrates to make the list of the world’s 100 worst invasive species, they’ve had major economic impacts on shellfisheries in New England, including blue mussels, the Virginia oyster (Crassostrea virginica) and Bay scallops. Impacts are mounting on the west coast too, where losses to bivalve fisheries (Pacific littleneck, Japanese littleneck, softshell clams and blue mussels) are projected to reach $20,000-60,000 per year. Ecologically, their impact has been no less severe, as they prey on and compete with other crabs, bivalves, gastropods like snails and slugs, and many other invertebrates.
Green crabs are exceptional world travelers, making it from their native region along the European Coast to six major regions of the world, including the Northwest Atlantic (Maryland to Newfoundland), the Northeast Pacific (California to British Columbia), Patagonia, South Africa, Japan and Australia. Their mode of transport may vary, but evidence suggests they’ve been transported with the live-bait trade and in ships’ ballast water.
Green crabs have been on the East Coast of the US for about 200 years, according the NEMESIS database. They made their first appearance near New Jersey in 1817. From there they moved north, reaching the Bay of Fundy, Nova Scotia in 1953, the Gulf of St. Lawrence by 1994, and finally, Placentia Bay, Newfoundland in 2007. Their southward expansion stopped at the Chesapeake Bay; possibly they couldn’t compete with the blue crab (Callinectes sapidus).
by Katrina Lohan
We had very little trouble finding two of the oyster species we needed at three different places. But with only three days left in our trip, we had yet to find Ostrea sp. at more than one location. With our hopes high, we headed toward Portobelo to see if we could find a saline river-like environment that had Ostrea sp. in high enough abundance for us to sample. The drive was gorgeous! We drove along the Atlantic Coast of Panama and stopped at five separate “rivers”, though most of them were pretty small and should probably be called streams instead. We also briefly drove into Portobelo so that we could drive past the old Spanish forts in the city.
We only found Ostrea sp. at one of the rivers, and we didn’t find enough to sample there. Our final stop on our way back to Naos was the French Canal. We had borrowed an inflatable canoe from Mark Torchin, which took us about 20 minutes to pump up. Once we did, we were able to get the canoe into the water and used it to more closely investigate what oysters were growing on the bridge pilings. We had our fingers crossed that it would be Ostrea sp. but, alas, it was Crassostrea sp. instead. Well, I can’t be too upset. While we didn’t get the ideal sampling we were hoping for, it was still a very successful trip!
Next month we head to Merida, Mexico to continue our sampling adventures. Stay tuned!
by Katrina Lohan
The day after arriving in Panama City, we went out into the field to continue collecting. During our trip in December, we had sampled two locations on the Atlantic side of the Canal. Now we had to complete our sampling for the three genera we had been sampling in Bocas. So we headed out to an area near Colon, Panama, and rented a boat for a few hours to go find oysters in the mangroves. We were successful at finding all three species at one location and two of the three species at another location. Not bad for a single morning.
by Katrina Lohan
We were able to find a final location for Ostrea sp. in Bocas del Toro, which wrapped up our sampling there. So it was time to return to Panama City to complete our sampling on the Atlantic side of the Panama Canal.
Now I have been trying to learn and remember some Spanish phrases. There were times when my lack of fluency was awkward, and other times when it is more problematic. Our return trip to Panama City was one of the problematic occasions!
by Katrina LohanTo satisfy our sampling scheme, we needed one more location with all three genera present. The dock at Bocas del Toro wasn’t the most glamorous location to sample, but it was an amazing place to snorkel around. There were many bivalve species and an abundance of individuals for each species located on the pilings. There were lots of different fish, coral, hydroids and sponges. It was beautiful! We decided to make this our third sampling location as it was easily accessible and had all three species–or so we thought.
We know oysters are tricky to morphologically identify, as they have such a wide range of growth patterns. It wasn’t until we were back in the lab and had shucked a few of the oysters open that we realized what we thought was Ostrea sp. in the field was actually a different species, Dendostrea frons. Oops…
by Katrina LohanFor the second oyster sampling excursion, we headed out to Bastimentos and Solarte to try to find another site where the same three oyster species co-occur. Unfortunately, Kristy was out of commission at the time due to illness (though I’m happy to report that she has made a full recovery).
Mark, Greg and I had scouted out a few potential locations the night before. While we had no trouble finding Isognomon sp. and Crassostrea sp. on the mangroves in multiple locations, we struggled to find a location where Ostrea sp. occurred with them. So, when we ventured out to collect in the morning, we decided to scout out a few more locations that might have all three species. At Solarte, we found just the right spot! Collecting all the oysters we needed didn’t take long at all, so I suggested that perhaps we do a little snorkeling while on our way back to the field station. Mark knew just where to go. We ended up snorkeling at a place called Hospital Point, where I saw a spiny lobster (Panulirus argus). Then we stopped at another snorkeling spot with huge sea stars, cute sandy gobies, sea cucumbers and beautiful coral!
The extra time spent in the water was just what I needed to motivate myself to get into the lab and process some oysters, as I knew that any data I helped generate would add to the ever-growing body of knowledge about the world beneath the waves!
by Katrina LohanOur first sampling site was Punta Caracol. We were able to find three oyster species attached to the mangrove roots at this site, including Ostrea sp., Crassostrea sp. and Isognomon sp. The salinity was about 30 parts per thousand, so well within the acceptable range for the three protozoan parasites that we are hoping to find.
I spent some time on the boat, but I desperately wanted to get in the water. Thus, when we had trouble finding Ostrea sp., I eagerly offered to jump in and snorkel around in the mangrove roots to look for more individuals. While I wasn’t too successful finding that species in the areas I was looking, I greatly enjoyed getting into the mangrove trees to search for them! I saw xanthid crabs, sponges and lots and lots of barnacles! We did eventually find enough individuals from all three species, at which point we headed back to the lab to process all the oysters.
Being in the water was definitely the best part of the day!
by Katrina Lohan
After spending less than a week at the Naos Laboratory, Kristy and I headed to Bocas del Toro with collaborator Mark Torchin from STRI and my advisor, Greg Ruiz from SERC. The flight from Panama City to Bocas del Toro is only about an hour, so we left on the first flight out in the morning and arrived at the station in plenty of time to put in a full day’s work. Though tired from getting up early to make the flight, there is nothing that wakes me up faster than a chance to get in the water!The majority of our first day was spent settling in. We had a safety orientation with Plinio Gondola, the Deputy Scientific Coordinator at the field station. We then unpacked the gear and quickly took over our assigned space in Laboratory 100. Next it was time to settle into onsite accommodations. The Bocas del Toro field station has dormitories as well as houses for visitors. We are staying in one of the houses, the Casa Hoch, which has two rooms, a dining room, lounge area and full kitchen. Excellent accommodations!
After settling in, we decided to do some reconnaissance in hopes of determining at least one potential sampling location. Kristy, Greg, Mark and I headed out on one of the marine station’s boats to find oysters. We spent most of the time searching mangrove roots attempting to determine what species were present in the different locations we were surveying. While driving around the mangroves is nice, I particularly enjoyed the reconnaissance that involved snorkeling. While snorkeling, I was able to check out potential pathogen reservoirs in addition to noting the bivalve species in the area. So many research options and so little time!
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