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Chesapeake Bay News


'Zombie' crabs invade the Chesapeake Bay

Imagine you are going about your day as usual when you encounter a foreign creature. It injects something in you, but does not kill you. Over the next few weeks, you notice a growth in your abdomen. A network of tube-like threads spreads throughout your circulatory system. Soon, you start losing control of your motor functions. You adopt defensive postures and develop maternal instincts to care for the growth instead of caring for yourself. Then, the mass begins to expel larvae, which seek out and infect anyone nearby. Your behavior is forever changed and your reproductive system destroyed.

Darin Rummel holds a black-fingered mud crab at the Smithsonian Environmental Research Center in Edgewater, Md., on Oct. 15, 2015. Rummel works in the lab of Carolyn Tepolt studying the "zombie crab" parasite called Loxothylacus panopaei, or Loxo.

This scenario may seem like something out of a science fiction novel or the latest zombie thriller. But for many black-fingered mud crabs, the parasite Loxothylacus panopaei, or loxo, has made this situation a reality.

Loxo was discovered in the Chesapeake Bay about 50 years ago. Scientists believe it was carried from its native range in the Gulf of Mexico on oyster shells during early restoration efforts. Since then, researchers have found sites throughout the Bay where the parasite is highly prevalent, with infection rates as high as 30 to 50 percent.

The tiny parasite Loxo is visible to the naked eye as white specks under a bright light, but practically disappears inside its host.

“This is huge, especially because this parasite is a castrator, so infecting crabs means they can no longer reproduce,” said Carolyn Tepolt, Biodiversity Genomics Postdoctoral Fellow at the Smithsonian Institute. “[The crabs] are still alive, but essentially dead as far as genes are concerned, because they are not contributing to the next generation of crabs.”

The Chesapeake Bay Parasite Project was established as a means for scientists to develop a better understanding of loxo by both monitoring infection rates in the wild and making observations in a lab, where research can be done in a controlled environment.

An infected black-fingered mud crab displays a Loxo egg sac on its abdomen. Infected crabs care only for the parasite eggs and lose the ability to reproduce.

“In 2013, I had the idea that it should be a citizen science project,” said Monaca Noble, Biologist at the Smithsonian Institute. “This isn’t a project that has its own grant money. It’s a project we do because we love it, so it’s always collateral duty for somebody. We thought it would be great to bring on volunteers.”

Through studying the prevalence of the parasite in both its native and invasive range, researchers now understand that loxo is much rarer along the Gulf Coast and up to Cape Canaveral, Fla., where one to five percent of crabs are infected. Tepolt and her colleagues are working to understand if reproductive pressures have affected these numbers over generations. “Say you’re a crab and you have some little mutation that makes it a little harder for the parasite to infect you, you may have a huge evolutionary advantage if 50 percent of your peers are getting taken out of the gene pool,” said Tepolt.

Black-fingered mud crabs from a sampling site in Louisiana await study in the lab of Biodiversity Genomics Postdoctoral Fellow Carolyn Tepolt at the Smithsonian Environmental Research Center in Edgewater, Md.

Citizen science has proven to be a valuable method for studying loxo’s reach and the population of affected crabs. Noble and her team have seen a steady increase in volunteer numbers, with 89 participants this past summer compared to 50 in 2014.

“I love [The Chesapeake Bay Parasite Project] as a citizen science project,” explained Noble. “It’s an opportunity to share an exciting story about science with people who are interested and get them excited about science, and also tell them about invasive species.”

To view more photos, visit the Chesapeake Bay Program’s Flickr page.

Text by Jenna Valente
Images by Will Parson

Jenna Valente's avatar
About Jenna Valente - Jenna developed a passion for conservation through her outdoorsy nature and upbringing in Hawaii, Washington State and Maine. A graduate of Virginia Tech's Executive Master of Natural Resources program and University of Maine's School of Communication and Journalism, she welcomes any opportunity to educate the public about the importance of caring for the environment.


By the Numbers: 60

Three centuries ago, the Chesapeake Bay watershed was covered with trees. Maples, pines and oaks captured rainfall, stabilized the soil and offered food, shelter and migration paths to wildlife. But as the country was settled and developed, more people moved into the region, and forests were cleared for farms and communities and trees were cut for timber and fuel. The population of the region now stands at almost 18 million—more than double what it was in the 1950s. While valuable forests do remain in the region, many suffer from fragmentation: separation into smaller pieces that are vulnerable to threats.

Healthy forests capture rainfall, stabilize soil and offer food, shelter and migration paths to wildlife.

According to a report from the U.S. Forest Service, 60 percent of Chesapeake forests have been divided into disconnected fragments by roads, homes and other gaps that are too wide or dangerous for wildlife to cross. The isolated communities of plants and animals that result have smaller gene pools that make them more susceptible to disease. The sensitive species that thrive in the moderate temperatures and light levels of an “interior” forest (which is mature and separate from other land uses) can’t find the unique habitat characteristics they need. And the forests themselves are more vulnerable to invasive species and other threats.

In the 1600s, forests covered 95 percent of the Chesapeake Bay watershed. In 2011, just 55 percent of the watershed was forested.

In an effort to reconnect fragmented forests, conservationists have turned to wildlife corridors. These corridors give wildlife the space to move and can be found around the world. The World Wildlife Federation runs the Freedom to Roam initiative to protect corridors along the Northern Great Plains and Eastern Himalayas. The National Wildlife Federation runs the Critical Paths Project to cut the number of fatal road crossings for animals in Vermont. And watershed states like Maryland and Virginia have incorporated wildlife corridors into their green infrastructure plans.

Virginia landowners Christine and Fred Andreae receive the Exemplary Forest Steward award from Craig Highfield of the Alliance for the Chesapeake Bay.

Even local landowners have contributed to the corridor movement: in September, the Alliance for the Chesapeake Bay recognized Christine and Fred Andreae as Exemplary Forest Stewards for their work to manage 800 acres of forestland—including a corridor that connects George Washington National Forest and Shenandoah National Park—along the Page and Warren county lines in Virginia.

Christine and Fred placed the property under conservation easement through the Virginia Outdoors Foundation, which was established by the Commonwealth in 1966. The Andreaes have also convinced their neighbors to follow suit: what started as an agreement between Christine, Fred and one neighbor to connect a patch of land on two sides of the Shenandoah River eventually expanded to include eight property owners and 1,750 contiguous acres. Today, bald eagles and bears abound on the land that can be seen from Skyline Drive.

“[Our neighbors] wanted to keep the land undeveloped,” Fred said when asked how he motivated others to join the conservation cause. “Most of them had family connections to the land—some [spanning] 100 years or more. It was their heritage they wanted to see preserved.”

The Andreaes have made their property as self-sustaining as possible so that once their two sons inherit it, it won’t have to be sold. “We’ve done something that will last. That’s a legacy. That will be there, theoretically, forever,” Fred said. “There aren’t too many things you can do that will be there after you’re gone—that will have an impact on my family and the other people who live in the area.”

Through the Chesapeake Bay Watershed Agreement, the Chesapeake Bay Program has committed to expanding urban tree canopy and restoring hundreds of thousands of miles of streamside trees and shrubs. Learn more about forests and our work to protect them.

Catherine Krikstan's avatar
About Catherine Krikstan - Catherine Krikstan is a web writer at the Chesapeake Bay Program. She began writing about the watershed as a reporter in Annapolis, Md., where she covered algae blooms and climate change and interviewed hog farmers and watermen. She lives in Washington, D.C.


Restoration Spotlight: Invasive plants got your goat?

Invasive species, or plants and animals that have been introduced to an area, can cause harm when they establish themselves at the expense of native wildlife. These invaders pose a threat to native species by outcompeting them for resources like food and habitat that are necessary for survival. Often, these species expand their range and population numbers at such a rapid pace that landowners and wildlife managers struggle to contain their spread.

Eco-Goats of Davidsonville, Md., devour invasive vegetation near the Severn River in Severna Park, Md., on June 24, 2015. Thirty-six goats spent a week clearing a path to Hatton Memorial Beach.

Brian Knox is President of Sustainable Resource Management, Inc., a natural resource consulting firm based out of Davidsonville, Md., that deals primarily with managing forest vegetation. Knox has seen success in combating invasive plants by implementing outside-the-box tactics. “A lot of people these days are getting more conscious about their herbicide usage,” said Knox. “As a very small company, we’re not afraid to try anything.”

In 2007, Knox began unleashing a herd of goats—referred to as Eco-Goats—on areas overrun by invasive vegetation. The goats have proven to be a viable option for these problem areas, because they can go many places that people and machinery cannot reach, like steep slopes and hillsides. Additionally, because of the goats’ mouth shape and digestive system structure, they are able to grind up seeds in a way that ensures seeds are not returned to the soil to resprout at the end of the digestive process.

Brian Knox prepares to release his herd of goats on property near the Severn River in Severna Park, Md.

A herd of about 30 goats can work through about a half-acre of dense vegetation in 3 to 4 days. “Goats are very good at biomass reduction,” explained Knox. “Typically, a goat can eat about 25 percent of its bodyweight a day in green material. If you figure an average of 100 pounds, that’s 25 pounds of vegetation going into every goat that’s out there.”

Brian Knox of Sustainable Resource Management, Inc.

Although the goats are fond of invasive species like kudzu, porcelain berry, wine berry and mile-a-minute and are undeterred by thorns, they do not discriminate against native species. So before committing his goats to an area, Knox surveys each site to make sure the vegetation is appropriate. “A misapplied goat is every bit as bad as a chemical spill,” said Knox. “You can do damage with a goat... I look for native species and ask, ‘Is there more here to save than there is to get rid of?’ If so, that’s a terrible place for a goat.”

According to Brian Knox of Sustainable Resource Management, Inc., as many people become more conscious of their herbicide usage, alternatives like Eco-Goats are gaining in popularity.

Spending your day with a herd of goats may sound like fun, but managing the goats is hard work. “A lot of people think it’s just sitting around and watching the goats, and boy, that would be a great job. And then you talk to them about how it took me two days to get the fence up and I’m soaked through to my socks by eight in the morning,” said Knox. “But clearly there’s something that I really love about this. And it’s the educational aspect of it, seeing people’s eyes light up while watching the goats.”

To view more photos, visit the Chesapeake Bay Program’s Flickr page.

Images and video by Keith Rutowski
Text by Jenna Valente

Jenna Valente's avatar
About Jenna Valente - Jenna developed a passion for conservation through her outdoorsy nature and upbringing in Hawaii, Washington State and Maine. A graduate of Virginia Tech's Executive Master of Natural Resources program and University of Maine's School of Communication and Journalism, she welcomes any opportunity to educate the public about the importance of caring for the environment.


Researchers observe ‘robust’ rockfish reproduction, spawning success

Striped bass spawning success has improved in the Chesapeake Bay, according to scientists from both Maryland and Virginia.

Image by Kenneth Summers/Shutterstock

Tracking the number of young-of-the-year striped bass in the Bay, or those rockfish that are less than one year old, helps scientists evaluate the health of the striped bass stock. To determine this number, scientists take a series of seine net samples in select striped bass spawning areas—like the Choptank, Potomac and Nanticoke rivers in Maryland and the Rappahannock, York and James rivers in Virginia—each summer. The resulting “juvenile abundance index” serves as an early indicator of future fish populations, helping managers predict the amount of striped bass that will be available to fishermen in the coming years.

“Striped bass are a… resilient species when given favorable environmental conditions for reproduction and survival,” said Maryland Department of Natural Resources Secretary Mark Belton in a media release. “The robust reproduction should give Maryland anglers hope for a successful striped bass season in a few years’ time.”

In each Maryland sample, researchers caught an average of 24 juvenile striped bass; the state’s abundance index value rose from 4.06 to 10.67 this year, which is the eighth highest on record. In each Virginia sample, researchers caught an average of 12 juvenile striped bass; the Commonwealth’s abundance index value rose from 11.37 to 12, which is about equal to average historic values. There, striped bass spawning success has been average or above average in 12 of the last 13 years, which indicates consistent production in Virginia nurseries.

Striped bass hold great value in the watershed: the fish is a top predator in the food web and a critical catch for commercial and recreational fishermen. Fishing bans set in the late 1980s helped striped bass recover from harvest and pollution pressures, and experts now consider it a recovered species.

Learn more about the juvenile striped bass survey in Maryland and Virginia.

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