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Intern Logs: Mussels and the Melting Arctic

Thursday, April 3rd, 2014

by Amanda Guthrie, Marine Invasions Lab Intern

Mytilus mussels in Point Judith Marina, Rhode Island. (Photo by Kim Holzer)

Mytilus mussels in Point Judith Marina, Rhode Island. (Kim Holzer)


Imagine after settling down on a place to stay, your home picks up speed and moves without any forewarning, bringing you along with it to a new place. You get off to explore. It seems livable and similar to home, but a few adjustments will be necessary.

This story would be possible — if you were a mussel, a barnacle, or a myriad of other intertidal organisms. Once there, these new arrivals are sometimes able to escape their predators at home and thrive—often at the expense of native species, or the ecosystem as a whole.

Such is the dilemma of Mytilus galloprovincialis, a mussel from the Mediterranean. Mytilus galloprovincialis is native to southern Europe but has branched out to numerous non-native regions around the globe. It is the most prevalent non-native marine species in South Africa. There, it not only competitively displaced native species but also catalyzed the decline of swimming crabs and the increase of whelks.

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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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Of Censusing Trees and Elephant Dung

Friday, November 22nd, 2013

by Kristen Minogue

Herve Memiaghe, front, in Gabon’s Rabi forest plot. The red line marks where they measure the tree’s diameter. (Smithsonian Institution)

Herve Memiaghe isn’t the average intern. Before coming to the Smithsonian Environmental Research Center, the 33-year-old Gabonese ecologist had already earned a master’s degree and spent four years working at IRET, the Institute for Research in Tropical Ecology in Gabon. Since 2012 he has also done field work in the Rabi plot as part of the Smithsonian’s global forest study.

The 25-hectare Rabi plot sits on the southwest coast of Gabon. Diversity spikes in the rainforests of Central Africa, where a single hectare can contain more than 400 different species. And that’s just the trees. The animals bring problems of their own. In Memiaghe’s experience, it’s not uncommon for hungry elephants to eat the tree tags along with the leaves.

“Sometimes we find the tag in the dung of elephants,” Memiaghe says. Usually the scientists can figure out where the tag came from, so it doesn’t throw off their research that much. “It just maybe can be a mess for the new people.”

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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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New Path for Summer Education

Monday, September 16th, 2013

by Kristen Minogue

7-year-old Cecilia Bowers collects frogs in the SERC forest. (SERC)

7-year-old Cecilia Bowers collects frogs in the SERC forest. (SERC)

It’s 2 o’clock in the afternoon. In the forest beside SERC’s beaver pond, Dylan McDowell and Shelby Ortiz have just finished helping a dozen 7-to-9-year-old students search for frogs and toads. They’re headed to the stream when McDowell runs into a dilemma: Some of the children don’t want to release their frogs.

“It would be really hard to find frogs around where I live,” says Emma Guy, who doesn’t have any parks or forests near her home.

“Did you know a couple years ago, they found a brand new species of frog in New York City?” McDowell asks her. He’s referring to a new species of leopard frog confirmed in 2012, whose known range has Yankee Stadium almost dead center. Closer to home, SERC biologists discovered juvenile eastern spadefoot toads in one of its wetlands this summer—the toad’s first recorded appearance on the SERC landscape. McDowell’s point, at least for the afternoon lesson: Amphibians can appear almost anywhere if you know where to look.

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Trees, Poison Ivy and Climate Change

Monday, August 12th, 2013

By Katie Sinclair

Hopetree

Intern Hope Zabronsky measures the diameter of a tree to see how logging affects biomass regeneration

Summer is almost over, which means intern season is coming to a close. Over 20 interns from universities across the United States have spent their summers here at SERC, studying everything from phytoplankton to Phragmites. Several interns chose to take on the challenge of climate change, exploring how trees will affect rising levels of greenhouse gases.

Mysterious Methane

Although methane emissions worldwide are much lower than CO2 emissions, a little methane goes a long way: Methane is 25 times as powerful a greenhouse gas as CO2. While we have an idea of what the sources of methane are, researchers face difficulties when trying to model methane emissions. The biggest discrepancy is between “top-down” and “bottom-up” models. Top-down approaches use satellite imagery to track the amount of methane in the atmosphere, while bottom-up methods look at the amount of methane emitted from the soil.
The Biogeochemistry Lab wants to see if methane is coming from sources other than the soil. Marsh grasses are known to emit methane, but no research has yet been done on trees. Figuring out if and how much methane is emitted can help determine whether methane projections are accurate. The Biogeochemistry Lab has set up two experimental sites to study methane, and is working on establishing a third.

Intern Kyle King worked on methane emissions this summer. He attached airtight chambers to trees, and measured the gas concentrations at different heights along the tree. He found that trees did emit methane, in some cases more than microbes in the soil. Methane emissions were highest near the roots and less at higher trunk heights. He also found that larger trees emitted much more methane than smaller ones.

The exact mechanism of how trees release methane is not yet understood. Two possibilities are methane diffusing out of the water that is taken in by the plants’ roots, or microbes inside the tree producing methane. But whatever the cause, understanding where methane comes from will be vital when trying to predict the impact of climate change.
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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
crabpic
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.

Mangrove Tracking VII: Just Another Day at the Office

Monday, July 16th, 2012

by Nancy Shipley

Technician Lorae Simpson and intern Jake Bodart deep in the mangroves, assessing vegetation cover and substrate color. (Mayda Nathan)


It sometimes seems crazy to be climbing through mangrove stands and wading through large ponds to collect our data, but the sites we explore are chosen for a reason. That reason is two-fold: One, to ground truth satellite imagery so we can map historic and current mangrove distributions. Two, to document the plant communities in places dominated by mangroves, in places where mangrove encroachment is occurring, and in places where mangroves have not yet arrived.

By using satellite imagery from years past, we hope to determine how far mangrove communities have spread in the last few decades. To do this we have to first understand what individual plant species comprise the large areas of vegetation that we can see from the satellites.

That is where we come in, climbing through mangroves.

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Mangrove Tracking VI: Attack of the Beetles

Thursday, July 5th, 2012

by Jake Bodart

Beetle tunnel. This Scolytid beetle has burrowed into a mangrove seedling and lain its larvae inside. (Jake Bodart)

In science not everything goes according to plan. For example, half of your project’s experimental units might die before you start.

In the back of the Smithsonian Research Station here in Ft. Pierce, the mangrove team has built an artificial pond (we call it Lake Simpson) to raise mangrove seedlings that will be used in experiments. However, when we arrived here last month, we noticed that about half of the red mangroves were turning black and dying. It was unclear at first whether these mangroves were dying directly as a result of the artificial habitat (was our pond too hot? Too salty? Not salty enough?), or if the pond was somehow making the mangroves more susceptible to pest insects. We know from other studies that predation by insects can cause a large amount of propagule and seedling mortality.

Upon closer inspection, we decided insects were the culprit. The evidence of insect predation: small bore holes and little piles of frass (chewed up/excreted parts of the plant, a.k.a. insect poop). We decided to sacrifice the seedlings that were clearly infested, and dissect them to see if there were any insects inside.

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Toughest Shellfish in the Sea?

Tuesday, January 24th, 2012

by Kristen Minogue

Blue mussels (Credit: Meriseal)

Some species can survive just about anywhere. Take blue mussels, a group of shellfish whose habitat stretches from the Arctic to the Mediterranean. Over the last several decades, biologists have thrown all kinds of tests at them – heat, cold, saltwater, freshwater, low oxygen. They’ve even tried drying them out. Almost nothing fazes these animals. For invasion scientists trying to figure out how far they could spread, that’s a scary prospect.
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