Invasive Species

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From the Field: Oyster Parasites Through a Microscope

Thursday, June 13th, 2013

by Katrina Lohan

Microscopic cysts inside a Crassostrea virginica oyster. (Katrina Lohan)

Microscopic cysts inside a Crassostrea virginica oyster. (Katrina Lohan)

In addition to taking oyster tissue to test for the presence of protistan parasites, we are also analyzing the oyster tissue for larger, but still microscopic, parasitic species such as worms, trematodes, and copepods. We have found parasites in all the species examined in all the locations we have traveled, but I got the best pictures of critters observed in oysters in Florida!

The highest prevalence and density of parasites occurred in Crassostrea virginica oysters. So far, I have seen copepods, turbellarians (probably Urostoma sp.), pea crabs, gill parasites, and cysts (probably from cestodes). I even saw what looked like a fish embryo, which was probably just brought into the gills, and an insect larva. Seeing all these critters under the microscope has made me contemplate why oysters are considered an aphrodisiac!

From the Field: Sea Wall Scraping

Wednesday, June 12th, 2013

by Katrina Lohan

Sea wall coated with oysters at South Bridge Marina. (Kristina Hill)

Sea wall coated with oysters at South Bridge Marina. (Kristina Hill)

Our second sampling location was a sea wall adjacent to a marina just below the south bridge in Ft. Pierce. The water was shallow enough along the wall that we were able to get out of the boat and stand in front of the wall, which made hammering and scraping the oysters off of it much easier!

Just as before, finding enough Crassostrea virginica oysters was easy, but finding the other oysters…took a lot more scraping. The Isognomon sp. at this location were fairly small and tucked into the crevices created by C. virginica, so they could be harder to spot. I took a step-wise approach, collecting the easiest species first, then making sure I had enough Isognomon sp., and only then did I move on and attempt to locate Ostrea sp., which easily took up the majority of our time. Most of the individuals in this species were dime-sized or smaller, tucked into the crevices or even in the dead shells of other oyster species, and they were covered in turf algae and mud. It took me (and the others) about an hour to find a sufficient number of these little guys at each of our respective sampling sites along the wall.

The funniest part of sampling along this wall was that there were lots of people around who did not hesitate to yell out! I am grateful to the multiple individuals who were concerned for our safety and mentioned the pilings in the water near the wall. (The water was clear enough to see them and we walked very slowly. Also, we all wore hard-bottomed water shoes and thick gloves.) We also had multiple boaters that were traveling in and out of the marina ask what we were doing, though I think some of them probably thought that we were just there to clean off the seawall!

Once all the oysters were collected, I took one water and one subtidal sediment sample and put them on ice. Then it was back to the lab to process more oysters.

From the Field: Dolphins!

Tuesday, June 4th, 2013

by Katrina Lohan

 A dolphin surfaces in Indian River Lagoon, Fla. (Kristina Hill)

A dolphin surfaces in Indian River Lagoon, Fla. (Kristina Hill)

We soon learned that it is mating season for dolphins and they frequently visit the Indian River Lagoon. On our boat trips to sampling locations, we have seen dolphins twice, and both times they were engaging in courtship behaviors. They are such graceful creatures.

I have to admit that I really, really want to see a manatee, another commonly spotted marine mammal in the lagoon. I haven’t spotted one yet, but I’m keeping my fingers crossed!

More on dolphin courtship >>

View manatee spotted in Florida mangroves >>

From the Field: Biofilms and Sediments

Monday, June 3rd, 2013

by Katrina Lohan

Kristy Hill uses cable ties to secure  a "biofilm collector" (a.k.a. microscope slides in a container) to a cage suspended from a local dock. (Katrina Lohan)

Kristy Hill uses cable ties to secure a “biofilm collector” (a.k.a. microscope slides in a container) to a cage suspended from a local dock. (Katrina Lohan)

As you may recall from a previous blog, part of the research for my fellowship project involves using genetic tools to look for parasites outside of their host organism in order to increase our understanding of the general ecology of these parasites.

I have been collecting water samples at all of the oyster sampling locations, but I decided that I wanted a larger diversity of habitat types. Thus, after discussing this idea with my advisors, I have decided to also sample subtidal marine sediments at the oyster sampling locations and collect biofilm samples. I will use the same genetic techniques on all the sample types to examine the diversity and distribution of marine parasites associated with the different habitats.

To collect the biofilm samples, we are using microscope slides, which were secured into a slide holder and suspended off of a local dock. The plan is to them scrape the biofilm off the microscope slides at scheduled intervals during our trip. I can’t wait to see what’s growing on them in a few days!

Read more on parasites surviving in disease reservoirs >>

From the Field: Parasite Hunting in Florida

Friday, May 31st, 2013

by Katrina Lohan

Jack's Island oyster reef in Indian River Lagoon, Fla. (Katrina Lohan)

Jack’s Island oyster reef in Indian River Lagoon, Fla. (Katrina Lohan)

For our next parasite hunting adventure, Kristy and I will be spending two weeks on Florida’s Atlantic Coast at the Smithsonian Marine Station at Fort Pierce. The marine station is located on a beautiful lagoon. We arrived on Monday and got a warm welcome from the staff, a thorough tour of the facilities and unpacked all of our gear, all four boxes of it. (No, we don’t travel light!) While here, we are staying on campus at the Taylor house, which is a residence for visiting scientists complete with kitchen, full bathroom, and a beautiful wrap-around porch that faces the water. We have long days and nights on these field trips, so it’s nice to have close accommodations that allow us to easily get back and forth to the lab, along with a full kitchen so we can cook quick and easy meals before returning to processing oysters. So far, I’m impressed!

On Tuesday, we headed out to our first field location. We hopped in a small boat owned by the Smithsonian and went to Jack’s Island, an oyster reef surrounded by mangrove trees. We were able to easily find Crassostrea virginica, as it is the species that makes up the reef, and then had to spend a little more time searching for Isognomon sp. at each site to get the numbers we needed. Also, it’s virtually impossible to tell which oysters are Ostrea sp. without opening the shells, so hopefully we have enough of those….

We also had a new first at this site—this is the first time that we have had a tour boat pass us while we were collecting!

Read accounts of marine biologists hunting for oyster parasites in Panama >>

From the Field: Insects Behind the Mangrove Invasion

Thursday, May 30th, 2013

by Mayda Nathan

Many insects visit black mangrove flowers, including bumblebees (left) and Pseudomyrmex ants (right). But which pollinators are the most important? (Mayda Nathan)

Many insects visit black mangrove flowers, including bumblebees (left) and Pseudomyrmex ants (right). But which pollinators are the most important? (Mayda Nathan)

Introduced species have a bad—and sometimes well-earned—reputation. Brown tree snakes in Guam, mosquitoes in Hawaii, cheatgrass in the intermountain west, and many more invasive organisms have turned native ecosystems upside-down, changing fundamental ecosystem properties like species diversity, nutrient availability, and the size and shape of food webs. Biologists are hard at work learning how to tell when, where, and how a species becomes a successful invader and driver of ecosystem change. (See a recent post on how tricky this can be.)

But how can we make predictions about invaders that are…native?

In other words, what happens when an organism starts to spread out from its native range into adjacent territory—without hitchhiking along with humans? And why does this happen in the first place?

Click to continue »

Invaders’ “Away-Field Advantage” Not as Strong as Once Thought

Thursday, May 16th, 2013

Brown tree snakes (Boiga irregularis) caused the local extinction of more than half of Guam's native birds and lizards after it invaded the island in the 1940s. (National Park Service)

Brown tree snakes (Boiga irregularis) caused the local extinction of more than half of Guam’s native birds and lizards after they invaded the island in the 1940s. (National Park Service)

by Kristen Minogue

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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Once an invasive, always an invasive?

Thursday, April 4th, 2013

by Monaca Noble and Paul Fofonoff

The European green crab has been on the east coast of the U.S. since 1817. (SERC)

The European green crab has been on the east coast of the U.S. since 1817. (SERC)

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.”

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As Green Crabs Invade, Alaskans Launch Counteroffensive

Thursday, March 14th, 2013

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.

European Green  Crab Carcinus maenas. Green crabs have visited every continent but Antarctica. They've colonized parts of the Americas from Alaska to the southern tip of Argentina. (Arthro)

European Green Crab Carcinus maenas. Green crabs have visited every continent but Antarctica. They’ve colonized parts of the Americas from Alaska to the southern tip of Argentina. (Arthro)

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).

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From the Field: One Final Search

Tuesday, February 26th, 2013

by Katrina Lohan

Sunset from the dock at the Bocas del Toro Marine Station, Smithsonian. (Katrina Lohan)

Sunset from the dock at the Bocas del Toro Marine Station, Smithsonian. (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!

Complete parasite-hunting stories from Panama >>