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From the Field: High and Dry in Chesapeake Bay

Thursday, December 19th, 2013

How an invasive marsh plant could leave many fishes and invertebrates homeless, hungry and vulnerable to predators

Ecologist Heather Soulen (right) wades through a patch of Phragmites in Chesapeake Bay. (SERC)

Ecologist Heather Soulen (right) wades through a patch of Phragmites in Chesapeake Bay. (SERC)

by Heather Soulen, SERC marine ecology lab technician

It’s no surprise that invasive species can dramatically alter an ecosystem. Often, invasive species outcompete native species and disturb ecosystems that have not evolved to handle the new intruder(s). One such invader is the introduced common reed (Phragmites australis australis). Introduced Phragmites alters native plant communities that native animals use. Over the past several decades, native marshes containing plants such as marsh elder, saltmeadow hay, black needlerush, sea lavender, cordgrasses, threesquares and bulrushes have fallen to introduced Phragmites in the Chesapeake Bay and throughout the Atlantic coast, turning once diverse marshes into a thick monoculture forest.

The Great Marsh Surface Uprising
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Cracking Down on Mercury

Monday, December 9th, 2013

by Kristen Minogue

Ally Bullock, a technician in SERC's mercury lab, draws pore water samples from Berry's Creek. (SERC)

Ally Bullock, a technician in SERC’s mercury lab, draws pore water samples from a mid-Atlantic Superfund site. (SERC)

There are places in the U.S. so polluted, eating fish or crabs from their waters isn’t just unhealthy—it can be illegal. The Environmental Protection Agency calls sites like that “Superfund sites,” a label for abandoned or neglected sites that became dumping grounds for hazardous waste. Some of the highest levels of mercury contamination in the U.S. exist in Superfund sites. Cynthia Gilmour knows this first-hand. As a microbial ecologist at the Smithsonian Environmental Research Center, she has worked in several.  But short of digging up the polluted sediments and dumping them elsewhere (an expensive and ecologically risky proposition), not many methods exist to get rid of the problem.

“If we use the traditional technologies of removing that and putting it in a landfill, we don’t have a wetland anymore,” says Upal Ghosh, an environmental engineer from the University of Maryland, Baltimore County, who works with Gilmour.

This fall, Gilmour and Ghosh explored a new technique: using charcoal to trap it in the soil.

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Intern Logs: Acoustic Telemetry
and Catfish Surgery

Friday, December 6th, 2013

by Brooke Weigel

Brooke Weigel displays a recently-caught blue catfish in SERC's Fish & Invertebrate Lab. (Katie Sinclair)

Brooke Weigel displays a recently-caught blue catfish in SERC’s Fish & Invertebrate Lab. (Katie Sinclair)

Have you ever wondered how far a fish can swim in one day? Acoustic telemetry enables researchers to track the movement, migration and behavior of fish. Beginning this past summer, the Fish and Invertebrate Ecology Lab started using acoustic telemetry to study the movement patterns of invasive blue catfish in the Patuxent River, a tributary of Chesapeake Bay.

Native to the Mississippi River, blue catfish were introduced for sport fishing in Virginia in the 1970s. Since introduction, these non-native top predators have expanded their range into many of Maryland’s tributaries. Their voracious appetites affect native fish populations and disrupt the food webs in these rivers. Blue catfish are the largest and most migratory species of catfish in North America. In their native waters, blue catfish have been known to migrate up to 200 km between different habitats used for spawning, feeding and overwintering. But little is known about their movement patterns within the Chesapeake Bay watershed, which is our motivation for using acoustic telemetry to track the movements of individual blue catfish.

Similar to radio tracking used to locate animals over vast distances, acoustic telemetry is a two-part system: Each fish has a transmitting tag, which emits a unique series of underwater sounds or “pings” at a random interval every one to three minutes. Stationary receivers then detect and decode these pings whenever a fish swims within range of the receiver. These detection data are converted to digital data and stored until researchers download the data onto a computer.

Interning at SERC for the past six months has given me the opportunity to be involved in every step of the process—some of which were messier than others.

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Decoding Nature: How DNA Can Save Species

Tuesday, September 17th, 2013

by Katie Sinclair

Katrina Lohan and Kristy Hill collect oysters on rocks near Punta Chame, Panama. (Carmen Schloeder)

Katrina Lohan and Kristy Hill collect oysters on rocks near Punta Chame, Panama. (Carmen Schloeder)

Katrina Lohan and Kristy Hill have travelled thousands of miles down the Atlantic Coast, from the Chesapeake to the Caribbean. Their goal? Track the range and distribution of parasites in bivalve mollusks that could cause disease. Based on diversity patterns, Hill and Lohan suspect that there are many more protist species in the tropics than have previously been discovered. These parasites could be very similar to the parasites that have caused mass die-offs in Chesapeake oyster beds with diseases like Dermo and MSX.

Close-up of a trematode oyster parasite. These parasites form cysts, and could be similar to the parasites that caused mass die-offs in the Chesapeake.

Close-up of a trematode oyster parasite. These parasites form cysts, and could be similar to the parasites that caused mass die-offs in the Chesapeake.

But there’s one catch: The protists that are parasitizing the bivalves are difficult to identify just by looking at them. Luckily for Lohan and Hill, advances in DNA sequencing can reveal secrets about little-studied and poorly understood organisms. Already famous for helping improve human health, DNA sequencing is proving equally adept at preserving the planet’s health. From the tropics of Panama to the forests of Maryland, the rise in DNA sequencing is opening new realms of possibility for ecologists at the Smithsonian Environmental Research Center and across the world.

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The Crab Tow Tango

Monday, July 29th, 2013

by Katie Sinclair

Brooke and Paige get ready to deploy the tow.

Brooke and Paige prepare to deploy the tow.

There is a certain art to the deployment of a crab tow. This brown metal and net contraption, about three feet long and a foot wide, scrapes over the bottom in search of juvenile blue crabs. Fitting three people, two coolers, a selection of buckets and bins and the tow in a 16-foot jon boat is something akin to a giant game of Tetris. Successfully launching and recovering the crab tow without smacking anyone in the face or knocking anything overboard requires practiced choreography and grace.

With a one-two-three, the metal tow hits the water with a splash. After 300 feet, lab tech Paige Roberts gracefully maneuvers the jon boat backwards and forwards to retrieve the tow. Paige captains the jon boat a bit like a fighter pilot—precision is required to coax the unwieldy boat around shoals, patches of sea grass and oblivious jetskiers. Click to continue »

From the Field: Oysters from Chincoteague

Tuesday, July 16th, 2013

by Katrina Lohan, Smithsonian postdoc

Kristy Hill and Michelle Repetto hunt for oysters on an exposed marsh in Chincoteague Bay. (Katrina Lohan)

Kristy Hill and Michele Repetto hunt for oysters on an exposed marsh in Chincoteague Bay. (Katrina Lohan)

For our final sampling site, we headed north to Chincoteague Bay. Edward Smith, our boat captain, had made sure to find a location that wasn’t currently leased to a local fisherman. He was confident we would find oysters, but he wasn’t sure about mussels or clams.

For some additional manpower, three summer interns from the Eastern Shore Laboratory accompanied us. Our sampling location was adjacent to Wallops Island, a NASA facility. We got to work as soon as Edward stopped the boat. Edward and the interns started raking for clams, while the rest of us grabbed oysters and mussels from the exposed marsh.

The mud here was also thick and deep! Once we had all the oysters and mussels necessary, Kristy and Michele aided in the search for clams while I recorded all the necessary metadata and took sediment and water samples. When the tide started to come in we had to halt our sampling efforts. Though we didn’t find as many clams as we wanted, we had enough to make processing them worthwhile. It was a great time for our final collecting trip of the season!

View full series on hunting for oyster parasites >>

Stomachs, Ear Bones and Electrofishing: Dissecting the Invaders

Friday, June 28th, 2013

By Katie Sinclair

SERCterms Mark and Brooke weigh and measure a bluecatfish.

SERC interns Mark and Brooke weigh and measure a blue catfish.

Ever wonder what a catfish eats? The blue catfish, invasive to the Chesapeake, is not a picky eater.

This voracious predator eats pretty much anything that can fit in its mouth.  By digging into their stomachs, a process vaguely reminiscent of high school biology classes, researchers can figure out the impact this species has on the ecosystem.

 In order to get some fresh catfish stomachs, researchers working in the Fish and Invertebrate Lab at SERC set up a “Gon’ fishing” sign and hit the field.

 Using a technique known as “electrofishing,” researchers stun the fish with electric currents in the water and collect them from several sites along the Chesapeake and rivers that feed into the Bay. Once the fish are caught, they place them into a cooler. The frozen fish are then identified by species, weighed and measured. Each fish varies tremendously: From a few ounces to over 10 lbs., a wide range of maturities and sizes are represented.

Paige and Mike begin to dissect the fish.

Paige and Mike begin to dissect the fish.

 A closer look at the stomach

A closer look at the stomach

The ecologists then remove the fish’s stomach,  taking great care to keep it intact. (Though frozen, the contents of a fish’s lower intestines tend to have a rather unpleasant smell). As fishermen know, gutting catfish can get messy, especially when the interns get involved.

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Mystery of the Missing Blue Crabs: Winter vs. Summer Young

Tuesday, June 25th, 2013

Republished with permission from the Blue Crab Blog. Check out the Blue Crab Blog for the latest news regarding Maryland’s favorite crustacean.

By Katie Sinclair, Guest Blogger and Intern at the Smithsonian Environmental Research Center
The blue crab may be the most well-known denizen of the Chesapeake Bay, with the blue crab fishery one of the most productive in the region. From the late 1990s to mid-2000s, the blue crab population was in decline, with a near record low population of blue crabs recorded in 2008. The cause of this decline is not fully known, but is most likely a combination of overfishing, habitat loss, poor recruitment, and poor water quality.

Since new regulations on crab harvesting, particularly those restricting the harvest of mature females, were put in place in 2008, the population of blue crabs has increased significantly. However, a low number of juveniles were caught in the winter dredge this year, leading to a gloomy forecast for the number of harvestable blue crabs for the 2013 season.

During my summer internship at the Smithsonian Environmental Research Center (SERC), I want to investigate if this forecast is coming true. The winter dredge survey, an extensive bottom trawl survey that catches blue crabs overwintering at the bottom of the bay, is impressive for its scale and precision. The survey takes into account 3 different regions of the bay, and 1500 sites are surveyed. The data are used to calculate crab density and from that project overall crab abundance. The 2013 winter dredge survey found markedly lower numbers of juvenile crabs (crabs smaller than 2.4 in) than in previous years.  One of the key questions regarding the survey, however, is just how closely the observed winter population of juveniles correlates with the actual number of blue crabs that survive to the summer.

One of the main issues with using the juvenile index from the winter dredge survey to predict future abundance of adult blue crabs is that it does not take into account survivorship of juvenile crabs, which can vary widely from year to year. Blue crabs are competitive and cannibalistic, and a large proportion of juvenile blue crab mortality can be attributed to predation by blue crabs themselves. Using the juvenile index to predict future adult abundances does not take into consideration interactions between adult and juvenile blue crabs—a low number of juveniles could in fact be the result of increased predation pressure from the adult population. Longer term research conducted at SERC has indeed shown that mortality of juveniles is related to the density of adult crabs.

Over this summer, research will be conducted to determine how adult and juvenile abundances from the winter dredge survey correlate with the actual numbers of blue crabs observed in the summer. Crabs will be collected by net tows and their abundance and size will be recorded. Similar research conducted last summer showed that the high numbers of juvenile blue crabs found by the 2012 winter dredge survey had vanished by the summer.

Hopefully for crab-lovers, the future low abundance of crabs projected by the low juvenile index of the winter dredge survey will be found to be too low. Recruitment rates for blue crab are known to fluctuate wildly, and survivorship of larvae to juveniles depends on multiple factors: salinity, temperature, dissolved oxygen, and predation. The winter dredge report did show an increase in mature females, which suggests that management strategies designed to protect fecund females are in fact working.

Research done at SERC comparing crab abundance and mortality brings to light interesting questions regarding the overall dynamics of the blue crab populations. The comparison of observed crab abundance in the summer to the juvenile index from the winter dredge report will help us determine how accurate the juvenile crab index is at predicting future crab abundances. Studying the population dynamics of blue crabs can help us understand and preserve this valuable natural resource.

Blue crabs decline–but recovery still on track

Tuesday, April 30th, 2013

by Matt Ogburn and Tuck Hines

Photo: Smithsonian Environmental Research Center

Photo: Smithsonian Environmental Research Center

To some following the blue crab recovery, the news earlier this month may have come as a shock. In 2012, the Chesapeake-wide Winter Dredge Survey estimated a record 764 million blue crabs in the Bay—the highest seen since 1991. Juvenile crab densities jumped to their highest levels ever. Then the 2013 survey released April 19 saw both those numbers drop.

Managers greeted the dwindling juvenile population with some depression. But those numbers may not matter as much, according to biologists Tuck Hines and Matt Ogburn of the Smithsonian Environmental Research Center. Ecologists at SERC have been tracking blue crabs for more than 30 years, almost a decade before the winter dredge survey began. They’ve discovered the population that really needs watching is the spawning females. Here is what the numbers are telling us:

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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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