Marine Lab Hunts Subtle Clues to Environmental Threats to Blue Crabs

The Atlantic blue crab, Callinectes sapidus, long prized as a savory meal at a summer party or seafood restaurant, is a multi-million dollar source of income for those who harvest, process and market the crustacean along the U.S. Atlantic and Gulf coasts.Unfortunately, the blue crab population has been declining in recent years under the assault of viruses, bacteria and man-made contaminants. The signs of the attack often are subtle, so researchers from the National Institute of Standards and Technology (NIST) and the College of Charleston (CofC) are at work trying to identify the clues that will finger specific, yet elusive, culprits.Pathogens and pollutants impair the blue crab's metabolic processes, the chemical reactions that produce energy for cells. These stresses should cause tell-tale changes in the levels of metabolites, small chemical compounds created during metabolism. Working at the Hollings Marine Laboratory (HML) in Charleston, S.C., the NIST/CofC research team is using a technology similar to magnetic resonance imaging (MRI) to identify and quantify the metabolites that increase in quantity under common environmental stresses to blue crabs -- metabolites that could be used as biomarkers to identify the specific sources.In a recent paper in Metabolomics, the HML research team describes how it used nuclear magnetic resonance (NMR) spectroscopy to study challenges to one specific metabolic process in blue crabs: oxygen uptake. First, the researchers simulated an environmentally acquired bacterial infection by injecting crabs with the bacterium Vibrio campbellii. This pathogen impairs the crab's ability to incorporate oxygen during metabolism. Using NMR spectroscopy to observe the impact on metabolite levels, the researchers found that the yield of glucose, considered a reliable indicator of mild oxygen starvation in crustaceans, was raised.In a second experiment, the HML team mimicked a chemical pollutant challenge by injecting blue crabs with a chemical (2,4-dinitrophenol (DNP)) known to inhibit oxidative phosphorylation, a metabolic process that manufactures energy. This time, the metabolite showing up in response to stress was lactate, the same compound seen when our muscles need energy and must take in oxygen to get more produced. A rise in the amount of lactate proved that the crabs were increasing their oxygen uptake in response to the chemical exposure."Having the glucose and lactate biomarkers -- and the NMR spectroscopy technique to accurately detect them -- is important because the blue crab's responses to mild, non-lethal metabolic stresses are often so subtle that they can be missed by traditional analyses," says Dan Bearden, corresponding author on the HML paper.The research was supported in part by the National Science Foundation.The HML is a partnership of governmental and academic agencies including NIST, NOAA's National Ocean Service, the South Carolina Department of Natural Resources, the College of Charleston and the Medical University of South Carolina.

Boosting Coastal Economics With Crustacean Molting On Demand

University of Alabama at Birmingham (UAB) researchers are close to unraveling intricate cellular pathways that control molting in blue crabs. The discoveries could revolutionize the soft-shell crab industry, generating new jobs and additional profits for the U.S. fishing industry along the coastal Southeast.

Soft-shelled blue crabs are a delicacy enjoyed by food lovers each spring and early summer when the crustaceans naturally molt their hard outer shell in the wild. Molting is the process by which the crab discards its exoskeleton, replacing it with a temporarily soft, pliable new exoskeleton that is easy to eat.

Despite being limited by the crab's annual molting patterns, the blue crab fishing industry is valued at nearly $50 million a year in Alabama, Florida, Mississippi, Louisiana and Texas. The ability to manipulate molting, or facilitate molting on demand, could make the blue crab available to consumers year-round, potentially boosting the industry's overall economic impact.

UAB biologist and researcher Doug Watson, Ph.D., and his research team believe they have identified the blue crab molt-inhibiting hormone (MIH) receptor, a key protein in the cellular pathway that controls molting. They are testing a compound designed to block the MIH receptor in the hopes of inducing molting.

"No one yet has isolated or characterized this MIH receptor for any crustacean, but we think we have isolated a gene that codes for that receptor," Watson says. "We're not 100 percent sure yet, but the gene we have cloned has all the characteristics of the MIH receptor. We're trying to determine for sure if it is."

Conceivably, then the growth of the animals could be controlled, and this could create jobs and stimulate local economies through private aquaculture or farming operations across every state touching the ocean -- from Texas to Maryland, Watson says.

"Induced molting probably would have to take place in an aquaculture setting because it would be difficult to control in the wild," Watson says. "Once the blue crabs molt in the wild they are very vulnerable to predators because their shell is so soft."

The identification and characterization of the MIH receptor also would constitute a significant contribution to the field of invertebrate endocrinology.

"That's the basic science and a key to answering the question of how growth and development are regulated in this group of organisms with so much ecological and economical importance," Watson says.

Watson says they will either need to develop an injection or food pellet that could be used to induce the molting process.

Watson's research is being conducted through a two-year grant funded by the Mississippi-Alabama Sea Grant Consortium and a pilot grant from the Center for Biophysical Sciences and Engineering at UAB. His research team includes colleagues Teruaki Nakatsuji, Junying Zheng and current UAB graduate students Hsiang-Yin Chen and Anna Pendleton.

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Adapted from materials provided by University of Alabama at Birmingham.

Crab discovery worries Chesapeake Bay researchers

The discovery of invaded species at Chesapeake bay area created worries among researchers by Gregory.The fuzzy-clawed crab that waterman Vince Meyer and his crew pulled from the Chesapeake Bay clearly did not belong there: it lacked the blue markings of the area's signature crustacean, plus it had hairy pincers. "He noticed it as soon as he saw it," Meyer said of his crewman, Henry DuPreez, who pulled in the creature in question, a Chinese mitten crab.This is the third year in a row watermen have found the invasive crab in the Mid-Atlantic bay, a development that worries environmental researchers and watermen.The species is not native to the region and can breed abundantly. If it becomes established in the area's waterways, no one knows how it might affect the Chesapeake's already-stressed ecosystem or its famous blue crab population."We can't predict what the impact would be," said Gregory Ruiz, a marine ecologist at the Smithsonian Environmental Research Center who examined Meyer's crab, now captive in an aquarium.He said the fear is the mitten crab would compete for food with the blue crabs, or eat them.Potential threats are not taken lightly. Blue crabs are the backbone of a major industry on the 200-mile-(320-km)-long Chesapeake Bay, the largest estuary in the United States. The crab harvest alone is worth more than $50 million, according to government figures.Chesapeake crabs are celebrated at fairs and festivals where crustacean queens are crowned and local craftsmen sell knickknacks and Christmas ornaments made from their shells.But mostly people eat them. Hundreds of crab shacks and seafood restaurants in the region serve them steamed to mallet-wielding patrons or pan-fried when the shells are soft. They are made into soups, dips, crab cakes and other delights.Limits have been placed on the size of the crab catch because of degraded conditions in the bay and concerns about the overall crab population, which a recent study found has been below target levels for a decade. The harvest is down from historical levels, but has been 50 million to 60 million pounds per year since 2000.About 170 invasive species have moved into the bay, contributing to its stressed condition. The nutria rodent is damaging marshes and the rapa whelk mollusk feeds on clams and oysters. Scientists say local species don't need any more competition, and that is the worry with the mitten crab."The concern is really the potential for high impact," Ruiz said, "but whether that would be borne out, I think, is not clear."Mitten crabs, a culinary delight in Asia, can be something of a nuisance. They are burrowers, exacerbating soil erosion. After establishing themselves in the San Francisco area in the early 1990s, they played havoc with the water system."The crabs basically were so abundant that they clogged water supply systems by clogging up filter screens," Ruiz said.They rear their offspring in freshwater tributaries, but migrate to shallower salt water areas to reproduce. Vulnerable blue crabs -- the babies and molting adults -- find refuge in the same kinds of habitats where mitten crabs breed, raising concerns they could become the invaders' prey.So far, there is no evidence mitten crabs are reproducing in the Chesapeake. The three examined by researchers were fully developed males. No females or babies have been seen.That suggests the mitten crabs found there may have been sucked aboard a ship taking on ballast water in Europe, Asia or San Francisco and then released into the bay when the vessel reached port. Researchers want to locate the source of the crabs, so watermen are on the alert as the summer crabbing season gets under way. For Meyer, who runs Vince's Crabhouse in the Baltimore suburb of Essex, Maryland, that means keeping a close watch as he checks his 500 to 600 crab pots each day. "They say they're not good for the bay," he said. "I guess they don't have predators and they're afraid they might maybe try to eat the blue crab."

Blue Crab not just for eating useful in Nano-Sensor Detects Dangers

A substance found in crab shells is the key component in a nanoscale sensor system developed by researchers at the University of Maryland's A। James Clark School of Engineering. The sensor can detect minute quantities of explosives, bioagents, chemicals, and other dangerous materials in air and water, potentially leading to security and safety innovations for airports, hospitals, and other public locations.

Clark School engineers are using a substance called chitosan (pronounced "kite-o-san"), found in the shells of the Chesapeake Bay's famous blue crab, to coat components of the microscopic sensor system.
Crab lovers can hold on to their mallets -- crabs do not need to be harvested specifically for this purpose. The material is extracted from the crab shell waste.
Reza Ghodssi, associate professor in the Clark School's Department of Electrical and Computer Engineering and the university's Institute for Systems Research (ISR), and a member of the Maryland NanoCenter , is one of the investigators leading the project. He is joined by a multidisciplinary group: Gary Rubloff from ISR and the NanoCenter, Bill Bentley from the Fischell Department of Bioengineering and Greg Payne from the University of Maryland Biotechnology Institute (UMBI).
"Chitosan is interesting because it's a biological compound that can interact with a wide variety of substances, and also work well in a complex, sensitive device," Ghodssi says.
Ghodssi's graduate students, Nathan Siwak, Stephan Koev, Jonathan McGee and Mike Fan, are helping to develop the nanoscale "system on a chip." It employs multiple miniature vibrating cantilevers, similar to diving boards (see photo to left), that are coated with chitosan, plus optical sensing technology that can see when the cantilevers' vibrations change (such devices are called micro-electro-mechanical systems or MEMS).
Different cantilevers can detect different substances and concentrations. When a targeted substance enters the device from the air or water, the chitosan on a specific cantilever interacts with the substance and causes that cantilever's vibration to change its characteristics. The optical sensing system sees the vibration change and indicates that the substance has been detected.
Ghodssi and his collaborators have recently submitted a proposal to the National Institutes of Health (NIH) to develop a sensor system to detect the presence of avian flu.
The technology was developed and initially tested at the Laboratory for Physical Sciences (LPS) in College Park, Md., and it is currently sponsored by LPS and the National Science Foundation (NSF).
"This is an exciting and complex microsystem that bridges biotechnology and nanotechnology to address critical needs of homeland security applications. My colleagues and I are expecting this work to become a product in the near future," says Ghodssi, who has to date filed for six patents on the technology.
Parts of this research were recently featured in the Journal of Micromechanics & Microengineering in April 2006 and the journal Biomacromolecules in November 2005.
Note: This story has been adapted from a news release issued by University of Maryland, A. James Clark School of Engineering.