|
A Mysterious Disease Afflicts Lobster ShellsSomething's rotten in the state of New England's favorite crustacean |
|
|
 | |  |
|
| Enlarge ImageAn image of a diseased lobster shows the ravages caused by epizootic shell disease, which has spread through New England waters. (Barbara Somers, Rhode Island Sea Grant & the University of Rhode Island) |
|
|  |
|
| Enlarge ImageThe disease causes black spots that often turn into deep holes in lobsters’ outer shells. The holes leave lobsters susceptible to bacteria or viruses and interfere with their ability to molt their shells and grow. In extreme cases, the entire shells rot, killing the lobsters. (Barbara Somers, Rhode Island Sea Grant & the University of Rhode Island) |
|
|  |
|
| Enlarge ImageWHOI biologist Tim Verslycke prepares to dissect a lobster specimen—for scientific, rather than gustatory, purposes. (Tom Kleindinst, Woods Hole Oceanographic Institution) |
|
|
Related Links |
|
|
In the late 1930s, lobstermen in Rhode Island began to notice strange
black spots on the shells of lobsters being held in tanks. By the
1980s, a similar condition, now known as lobster shell disease, started
to appear in wild populations.
Then in the mid-1990s, a more virulent form of the disease emerged in
southern New England waters. The black spots turned into deep holes in
lobsters’ outer shells. Holes often fully penetrated the shell, causing
the hard shell to fuse with soft membranes underneath. The disease left
lobsters susceptible to bacteria or viruses and interfered with their
ability to molt their shells and grow. In extreme cases, the entire
shell rotted, killing the lobsters.
Although the lobster meat itself is not affected, the unappetizing
appearance of afflicted lobsters makes them much harder to sell whole.
“Nobody would want to eat the thing,” said Bill Adler, executive
director of the Massachusetts Lobstermen’s Association. The disease was
a big factor in the 50-percent decline in lobster catches in Buzzards
Bay between 1998 and 2004, which forced many lobstermen out of
business, he said. At the time more than half of the lobsters in
coastal areas of southern New England and Long Island Sound were
affected by shell disease.
More recently stocks have begun to recover somewhat, Adler said, but up
to 30 percent of southern New England lobsters are still affected, and
the disease has started to show up in other areas, including Nova Scotia
and Maine.
What makes lobsters susceptible?
Researchers do not yet know what causes the disease or makes lobsters
susceptible, said Tim Verslycke, a biologist at Woods Hole
Oceanographic Institution. That point is reflected by the disease’s
name: epizootic shell disease. “Epizootic” simply means an outbreak of
a disease affecting many animals of one kind at the same time.
“Similar shell disease can be seen in any crustacean, but never to this
extent,” he said. “The levels we’re seeing here are really unusual.”
The epidemic could be the result of an accumulation of factors, Verslycke
said. Marine animals face many threats these days, including warming
ocean temperatures, fishing pressures, and increased exposure to
chemical pollution from industrial sources and pesticides.
Researchers have found that the disease is not contagious from lobster
to lobster, as is often the case with other lobster diseases. That
leads to suspicions that physiological imbalances or compromised immune
systems may be impairing lobsters’ ability to fight off the disease, he
said. Previous studies have found higher levels of certain chemicals in
shell-diseased lobsters than have been found in healthy lobsters. These
chemicals have been shown to disrupt the crustaceans' hormones systems, which could lead to a wide range of detrimental effects.
“At this point we’re trying to get an idea if these lobsters are indeed
exposed to chemicals at such levels that it leads to a lesser capacity
for them to cope with these diseases,” Verslycke said.
One clue comes from observations that make lobstermen especially
nervous: reports of egg-carrying female lobsters shedding diseased
shells with unhatched eggs still attached.
“This obviously means something is going wrong with their hormone
regulation,” Verslycke said. “It doesn’t make sense for them to molt
while they’re carrying broods. Normally, that is a very finely tuned
process that is hormonally regulated.”
“That’s where the fear of shell disease comes in,” Adler said. “There goes the future stock.”
The Lobster Shell Disease Initiative
Verslycke has examined the effects of human-made chemicals on
invertebrate hormone systems, including those that regulate molting.
“Lobsters can actually molt out of shell disease,” he said, “but
if they are exposed to a chemical that limits their capacity to molt or
otherwise interferes with their hormone systems, it would make them
more vulnerable to any kind of additional stress.”
In 2006, Verslycke and WHOI colleagues John Stegeman and Judith
McDowell were among nine teams of researchers funded by the $2.3
million New England Lobster Research Initiative, established by
Congress to study the causes and consequences of lobster shell disease.
Under the initiative, scientists from several institutions (including
the University of Massachusetts, the University of Rhode Island, the
New England Aquarium, Boston University, and the Marine Biological
Laboratory) are investigating the roles that microbes, contaminants,
and other environmental factors, such as warmer ocean temperatures, may
play in increasing lobsters’ vulnerability and fostering the spread of
the disease.
The WHOI study will examine how environmental
stresses, such as chemical exposure, might change the way specific
genes are expressed, or turned on or off, in diseased lobsters, as
compared to non-diseased ones. These genes produce proteins that
regulate the lobsters’ immune and hormone regulation systems.
“Our approach would allow us to evaluate whether genes associated
with these processes are indeed differentially expressed between
healthy and shell-diseased animals,” Verslycke said. “In other
words, we are hoping to find clues at the molecular level that indicate
why some animals are getting diseased and others not.”
—Sara E. Pratt
The New England Lobster Research
Initiative is managed by the National Marine Fisheries Service, the
University of Rhode Island, and Rhode Island Sea Grant.
Posted: October 18, 2007 [top] |
|
