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What is shell disease?

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.

University of Rhode Island Fisheries Center
East Farm Campus
Building 83
University of Rhode Island
Kingston, RI 02881