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Traps Full of Trouble: Diseases Take Toll on Lobster Fishery
by Tracey Crago, WHOI Sea Grant

Lobster man
The 1999-2000 lobster die-off in western Long Island Sound was declared a natural disaster. According to a study commissioned by the U.S. Department of Commerce, the disaster affected over one-third of Connecticut’s and half of New York’s lobstermen who fished the area. Photo credit: Julia Cumes, Cape Cod Times

When it comes to lobster disease, Long Island Sound lobstermen thought they had been there and done that.

In the early 1990s, Gaffkemia, a naturally occurring bacterium that infects the circulatory system of lobsters, caused high mortalities in the Sound’s lobsters.

But the fishery recovered and increased steadily, peaking in 1997, when 14.3 million pounds of lobsters were landed in the Sound. 1998 was another banner year, with 12.2 millions pounds landed. In 1999, however, Sound lobstermen found themselves hauling in more than they bargained for: lobsters in the eastern portion of the Sound had black spots on their shells; in the western portion of the Sound, limp lobsters, dead lobsters.

Not one disease, but two devastated the Sound’s lobster industry in a single year. Lobstermen, scientists, and fishery managers—aided by Congressional support of $13.9 million for economic assistance and research—joined forces to find answers. Sea Grant programs in New York and Connecticut are administering the research. Preliminary findings from several Sea Grant-supported researchers were presented in July at the 2002 National Marine Educators Association conference in Connecticut.

Chitinolytic Shell Disease

Kathy Castro, a fisheries specialist from Rhode Island Sea Grant, has been working on chitinolytic shell disease since 1995; that research is part of her Ph.D. dissertation, nearly complete. "With this disease, bacteria is eating away at the chitin in the shell," explains Castro. (Chitin is essential in forming the exoskeleton, or shell, of lobsters.) The disease, characterized by black spots on the carapace or shell, starts behind the eyes, progresses to the rostrum, then tail, says Castro; claws are the last to be affected. It is generally not lethal to the lobsters.

Castro and a colleague, Tom Angell, from Rhode Island Department of Environmental Management’s Fish and Wildlife division, monitored shell disease in lobsters caught in trawl and trap surveys from 1995-1999 in both nearshore and offshore locations in Rhode Island (shell disease was first noted in offshore populations in 1998). They reported a steady increase in the number of lobsters affected (up to 80 percent in some nearshore areas), a decrease in the size of lobsters showing signs of shell disease, and an increase in the number of lobsters re-infecting just after molting.

In Woods Hole, pathologist Roxanna Smolowitz of the Marine Biological Laboratory, is hoping to identify the bacteria responsible for this shell disease by using molecular and histological techniques. Her co-investigator in the New York Sea Grant-funded project is Andrei Chistoserdov of Stony Brook University.

In healthy lobsters, the carapace is comprised of a series of sequential layers permeated by seta (tiny hair-like stalks, used by lobsters for sensory perception) and cuticular pores. In diseased lobsters, Smolowitz has observed abnormal carapace features ranging from shallow lesions to moderately deep erosions, and what she calls early cuticular ‘pillar formations’ at the latter.

Smolowitz and Chistoserdov have sampled the lesion tissues for bacteria. Smolowitz is describing the lesions and the way the bacteria enter the carapace—initially, she believes, through the cuticular pores.

At the same time, Chisterodov has identified and isolated four types of bacteria present in infected lobsters using both culture and molecular techniques: Cytophaga sp., Pseudoalteromonas sp., Schwanella sp. and Alteromonas sp. Scanning electron microscopic examination has identified these bacteria burrowing into the carapace surface.

Assisting them in the project’s next phase is Andrea Hsu, a graduate student in the Boston University Marine Program. She has begun collecting lobsters from affected and non-affected fishing areas and will compare the bacterial isolates and histology between the new samples and those previously analyzed by Smolowitz and Chistoderov. Hsu recently received a Sea Grant Industry Fellowship through WHOI Sea Grant for this work.

Bruce Estrella, senior marine fisheries biologist with the Massachusetts Division of Marine Fisheries, is looking forward to Hsu’s results. "Making geographical comparisons to see if there are regional differences in the causative agent is very much needed," he says.

Limp Lobster Disease

Bruce Brownawell, an assistant professor at Stony Brook University’s Marine Sciences Research Center, is looking at the possible connection between pesticides and the lobster die-offs that occurred in 1999-2000 in the western part of the Sound. This connection is not without controversy: a lawsuit has been filed in New York civil court by lobstermen suing several pesticide companies.

In a timeline that might be considered a perfect recipe for disaster, Brownawell recounts how a pesticide spraying for mosquitoes in New York took place just prior to the arrival of Tropical Storm Floyd, which dumped eight inches of rain on the region, resulting in significant pesticide runoff into nearby wetlands and estuaries. "Such exposure to the pesticides or their more persistent metabolites," says Brownawell, "could have compromised lobster health in some way, making the lobsters vulnerable to infectious disease agents."

In Connecticut, Sylvain De Guise is also working the pesticide angle. De Guise, an assistant professor at the University of Connecticut’s Department of Pathology and Veterinary Science, is investigating malathion toxicity (a main ingredient in one of the pesticide applications used to control mosquitoes during the West Nile virus outbreak) by conducting experimental exposures. De Guise and his UConn colleagues, funded by Connecticut Sea Grant, have found a parasitic paramoeba in most of the lobsters examined during the die-off in the western portion of the Sound. And, while the paramoeba may explain the limp and weak conditions of afflicted lobsters, De Guise wondered what other causes or conditions might have made the lobsters more susceptible to the infection, thereby contributing to the high mortality.

De Guise has conducted laboratory tests to determine lethal and sublethal effects of malathion in lobsters. "The key," says De Guise, "is knowing what to measure, when. Toxicity can vary over time due to metabolism." Malathion, for example, degraded rapidly in De Guise’s laboratory experiments (65-77 percent lost after one day; 83-96 percent lost after three days), and could never be detected in tissues of lobsters with known exposure.

De Guise’s preliminary results establish a relationship between exposure and lobster susceptibility. "It appears that exposure to relatively low concentrations of malathion can affect lobster defense mechanisms, even with rapidly decreasing water concentrations," he says.

Future of Lobster Fishery

While the effects of the die-offs associated with the parasitic paramoeba continue to be felt in the Sound, shell disease has also afflicted lobster populations outside the Sound, primarily in Rhode Island, Massachusetts, and now, New Hampshire waters.

Estrella says this could mean one of three things. "Literature shows that shell disease occurs throughout the lobster’s range. We could be seeing a normal migration pattern in the disease itself, or it could be that the causative agent is moving. Another possibility," he says, "is that it could be both."

Throughout their range lobsters are labeled by the National Marine Fisheries Service as overfished. "Lobsters were once fished in a broader range," Estrella points out. "Now we are catching animals closer and closer to minimum size. This is now the case in the offshore environment as well as inshore: the size range has truncated." What this means, he explains, is that egg production responsibility is placed on the juvenile females in the population.

"What we have out there is like walking into a town with only teenagers, no older people," says Estrella. "This implies that we are dealing with a resource on the edge. It doesn’t take much of a change in environmental cues to sour the resource."

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