Full of Trouble: Diseases Take Toll on Lobster Fishery
by Tracey Crago, WHOI Sea Grant
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 Connecticuts and half of New Yorks
lobstermen who fished the area. Photo credit: Julia Cumes, Cape
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 Sounds 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 Sounds lobster industry
in a single year. Lobstermen, scientists, and fishery managersaided
by Congressional support of $13.9 million for economic assistance
and researchjoined 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
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 Managements 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 carapaceinitially, she believes, through the cuticular
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 projects 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 Hsus results.
"Making geographical comparisons to see if there are regional
differences in the causative agent is very much needed," he
Limp Lobster Disease
Bruce Brownawell, an assistant professor at Stony Brook Universitys
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 Connecticuts
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 Guises 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
De Guises 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,"
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 lobsters 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 doesnt
take much of a change in environmental cues to sour the resource."