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Researchers in the Northeast region first noticed
shell disease in the 1980s. At that time, the disease appeared
as little black spots affecting lobsters' shells. But in the
past several years, shells have sometimes become fully infected
by the disease with the worst cases rotting the shells entirely.
This new disease is called epizootic shell disease.
Shell disease is caused by bacteria that invade
from the outside of the lobster through pores in its cuticle
(the outermost layer of the shell) that cannot be seen by
the naked eye. There is a range in the severity of the disease
from shallow pits that eat away at the cuticle and cause those
unsightly black spots to ulcerations-holes that fully penetrate
the shell, causing the shell and the membranes underneath
it to fuse together. This can stop the lobster from releasing
its shell and can cause it to become stuck during the molting
process and die. A lobster needs to molt in order to grow.
It has been suggested that molting may be a defense mechanism
against shell disease. By molting, the animal can get rid
of the disease, if only temporarily, by losing its shell.
The disease does not taint the lobsters' meat,
but makes shells so unattractive that they are too unappetizing
to serve whole. The meat may be used for canning. Larger female
lobsters are the most severely affected because they retain
their shell for a longer period of time while carrying eggs.
It can weaken egg-bearing lobsters so much that they die prematurely.
Some preliminary studies suggest the lobsters
may be contracting the disease from alkylphenols, chemicals
that are byproducts from industrial sources. These compounds
are found in everything from detergents to surfactants (a
surface-active substance), paints, and plastics, and have
been found in higher concentrations in lobsters with shell
disease than in unaffected animals. These compounds may be
interfering with the lobster's normal hormonal system. In
the laboratory, it has been found that levels of the molting
hormone in shell diseased lobsters are much higher than unaffected
lobsters. Egg-bearing females should not molt during the nine
month period when they are carrying their eggs. Molting during
this time would cause the female to lose her entire clutch
of eggs.
More lobsters are getting shell disease, and
the problem is now found from southern New England waters
all the way to Maine. Thirty percent of lobsters in coastal
areas of southern New England and Long Island Sound are affected
by shell disease. It's still unclear what's causing it to
spread. Shell disease is not contagious from lobster to lobster,
and biologists suspect that environmental factors such as
water temperature or polluted run-off may be weakening the
lobster's immune system and allowing the bacteria to grow
faster than the lobster can fight it.
For more information, download "Shell Disease in Lobsters: A Synthesis," by J. Stanley Cobb and Kathleen Castro. See also Long Island Sound Lobster Initiative for information about research into lobster disease and mortality in Long Island Sound (New York Sea Grant website).
What is being done: New England Lobster Research
Initiative: Lobster Shell Disease
Research on lobster health is paramount to understanding the
causes and consequences of shell disease and other diseases
affecting the lobster stocks. Several lobster diseases have
been discovered that have occurred concurrently with the outbreak
of the lobster epizootic shell disease in SNE. In 1997, a
Vibrio fluvialis-like organism was implicated as the
etiological agent for the limp lobster syndrome found in Maine
(Tall et al., 2003). Lobsters affected with this syndrome
were weak and lethargic, had slow or ineffectual responses
to sensory stimuli, and had poor survival. The extreme lobster
mortality event that occurred in Long Island Sound (LIS) in
1999 brought to the forefront the link between stressed environments,
lobster health, and population-level effects. Believed to
be precipitated by the "perfect storm" of conditions
(Pearce and Balcom, 2005), a combination of high water temperature
and low dissolved oxygen, amoebae were found in the nervous,
glandular, connective, and branchial tissues of the dead lobsters
(Robohm et al., 2005). Also in LIS, calcinosis, a non-infectious
fatal disease of lobsters, was determined to be caused by
the anomalously high bottom seawater temperatures during the
spring and summer of 2002 causing changes in the acid-base
status and calcium metabolism resulting in calcium deposits
in the gills and antennal glands (Dove et al., 2004).
In 2000, a comprehensive lobster health initiative
began for LIS after the lobster mortality event lead to the
declaration of a fishery failure. This initiative was established
with a Congressional allocation of $6.6 million in federal
funds to NOAA for scientific research into the causes of the
die off and to monitor stock recovery. This program was cooperatively
managed by the New York and Connecticut Sea Grant programs
with their respective state fisheries agencies and the Atlantic
States Marine Fisheries Commission (ASMFC).
The continuation of funding dedicated to lobster
health is the backbone of understanding the effects of these
diseases on both the resource and the fishery. With this new
initiative, Congress has appropriated $3 million specifically
to establish a cooperative research program to study the causes
and consequences of lobster shell disease. This funding will
be jointly managed by the National Marine Fisheries Service
(NMFS) and the University of Rhode Island (URI) and Rhode
Island Sea Grant. A solicitation for research proposals is
expected to be issued in late May 2006. The goal of this project
is to describe the disease agent and how it works, and to
determine the extent and severity of the disease in New England
waters.
The specific objectives are:
- Provide spatial and temporal data on shell disease.
- Produce new information that can be used for understanding
the outbreak of shell disease and the consequences of shell
disease.
- Relay that information to other researchers, industry
and the general public.
- Develop a plan for continued funding beyond this initiative.
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