Lobster Shell Disease –
Hunting for an Answer
by Sandra Dinsmore
The disease is characterized by moderate to deep erosions on the carapace, which in severe cases may spread to the other parts of the lobster. Heavily affected animals literally can be covered with a rotted, weakened shell. Photo courtesy of Journal of Shellfish Research.
Everyone in the Maine lobster industry, no matter how peripherally connected, shares the fear of shell disease coming to Maine waters. This thing—it didn’t even have a name at first—eating away at lobster shells first appeared in inshore Rhode Island (RI) waters in 1996. It made the shells so unattractive, no one from housewife, to lobster shack server, to restaurant owner would want to put a lobster so affected before another person, much less ask someone to pay for the privilege of eating it.
Two years later, more than 20 percent of RI’s inshore lobsters and almost 80 percent of egg bearing females showed signs of what scientists now call epizootic shell disease, or ESD. (Epizootic means an outbreak of disease in an animal population, like an epidemic outbreak of measles in a grammar school.) Most fishermen and dealers call it shell disease, or shell rot. In 2002 and 2005 Roxanna Smolowitz and others described it in an understatement: “The disease is characterized by moderate to deep erosions on the carapace, which in severe cases may spread to the other parts of the lobster.” Heavily affected animals literally can be covered with a rotted, weakened shell.
Then in 1999, Long Island Sound (LIS) lobsters suffered a monumental die-off from which they have not yet recovered. Many LIS fishermen felt strongly that pesticides put in storm drains to kill mosquitoes were at least partly responsible for the die-off. The collapse of that commercial fishery led to almost $14 million in disaster relief to its fishermen and an investigation into what killed the Sound’s lobster.
The investigation, called the LIS Lobster Health Initiative, resulted in the publication of about 25 scientific papers, including several on pesticides and several more on this new lobster shell disease. But after the die-off, ESD increased from 20 to 35 percent in some areas of RI and began moving into Buzzards Bay and some other areas of southern Massachusetts (MA).
RI fishermen remembered a storm in January of 1996, during which some 2700 tons of No. 2 fuel oil had discharged into the waters off southern RI killing an estimated 9 million lobsters. Yet despite studies done in 1974 and 1983, in the end, Kathleen Castro, Ph.D., the University of Rhode Island (URI), Department of Fisheries, Animals, and Veterinary Sciences (DFAVS) wrote, “To date, there is no direct evidence that the oil or its dispersants were responsible for the initiation of shell disease.”
In 2003, shell disease showed up for the first time in Kittery, ME. The type of shell disease was not determined in a laboratory, however biologists believed most of the cases observed were ESD. During the 2003 and 2004 sampling season, according to Maine Department of Marine Resources (DMR), “Less than 0.05% of lobsters examined by staff were recorded as having shell disease.” That was gratifying, but in June 2004, “The largest number of shell disease lobsters observed during a sea sampling trip” occurred when 22 of 426 lobsters (5 %) were scored as having shell disease. Nevertheless, 2004’s numbers seem to have been an anomaly as shell diseased lobsters in Maine declined thereafter.
That the disease was increasing in a lobster population that was decreasing and that it also moving northward brought political action to study the problem. This, in turn, brought much needed research money to examine the cause or causes of shell disease.
In 2006, thanks to Maine (ME) Senator Olympia Snowe and RI Senator Jack Reed, Congress appropriated $3 million to the National Marine Fisheries Service (NMFS) to study the causes of ESD. NMFS administered the funds for ME, NH, and MA sea sampling, and sent the remainder directly to URI. After administrative expenses, $500,000 for ventless trap surveys, and $90,110 for outreach, money for research came to $1.945,905.
RI Sea Grant handled the proposal process and sent off requests for proposals. Then, from the 25 proposals received, reviewed and commented on, a technical committee selected nine research projects that, combined, produced 15 separate contracts for new studies.
Castro explained, “The final selections of projects to fund was based on quality of proposed research and need.” Three projects covered the disease itself; three covered the disease’s cause or causes, (things like bacteria); five projects studied the things that deviate from the normal to contribute to the disease (genes, minerals, senses); and four projects covered how the environment contributes to the disease. The overall project: “The New England Lobster Research Initiative” began in June 2006 and ended in June 2011.
Research began in January 2007. Over 35 scientists and graduate students representing 16 institutions and two state agencies went to work. The scientists wanted to understand how this outbreak of shell diseased happened and they wanted to relay that information to other researchers, to the lobster industry, and to the public.
That September. Castro said, “Several of us were at Prince Edward Island (PEI) for a lobster conference. We heard a talk by Michel Comeau [of Canada’s Department of Fisheries and Oceans (DFO)] about some New Brunswick lobsters they had caught with shell disease. Those lobsters had a lot of other problems as well.” She said as the lobster scientists involved in the shell disease research project sat there, “Somehow the idea emerged that we should all look at the same animals instead of looking at different ones; that way we would get an understanding of the whole animal.” Here they were, having spent much of the available research money, but knowing that they needed to try this. Castro said, “I couldn’t tell you whose idea it was, but Jeff Shields (Ph. D. of Virginia Institute of Marine Science (VIMS) at the College of William & Mary) said he would process [the lobster] if we got them and mail out all the parts and pieces and then get all the results and put them back together again. We all agreed,” she said. “It just made sense to everyone.”
Asked what led him to offer to organize this “100 Lobsters” project for free, Shields recalled that after Comeau’s presentation, researchers from New England (Castro, Jelle Atema [Boston University], Jan Facto[SUNY Purchase]r, Barbara Somers [URI], and Penny Howell [CT DEP]) were discussing what Comeau had found and whether it occurred in the Rhode Island lobsters. Shields said he walked in the room as Castro asked if anyone had looked at the tissue structure of the animals and whether we could add more of this into our investigations on ESD.
“As part of my investigations into many crustacean diseases,” Shields said, “my lab group and I do fairly routine collection of tissues for [that], and we’d just finished such on about 30-40 animals in our portion of the ESD study. So when [asked if] we’d seen similar internal [abnormalities], I could definitely state that we hadn’t, but we had been focused more on changes to the shell. So when they were wondering out loud whether someone in the US could do this for the ESD group, I naturally said, sure, we could incorporate our work on ESD.”
There followed much discussion about how to set up this new project. Shields said he offered assistance because, “ I saw that we could have a really powerful approach if we set it up properly.” He added that he had some funding from the New England Lobster Health Initiative and some discretionary funds generated through his other research project that could be used for additional work on ESD. Thus, he said, “The 100 lobsters’ project was born.”
This was not the case with all the other scientists. “We pooled travel funds and money to buy lobsters for everyone,” Castro said. Rhode Island sent 90 lobsters. (57 females and 33 males). Of those, 43 did not have shell disease (23 females and 20 males); and 47 had ESD (34 females and 13 males). Maine (DMR) sent 19 healthy lobsters (9 females and 10 males) to use as controls.
Shields and two technical staff received the lobsters, photographed them dissected and did tissue collection for each lobster, each of which took from 1 ½ to 2 hours to complete. He then sent the appropriate tissues to each researcher, many of whom were able to provide analyses on these additional animals.
During the five years of the project, the researchers had eight meetings to keep all the disparate sections and ideas up to date. “The research meetings were so interesting,” Castro said, “because everyone brought a different view to the results they shared, especially the chemistry (that no one understood) from Joe Kunkel.” The scientists also identified other lobster diseases such as Paramoeba-induced mortality, Orange Lobster Syndrome-Calcinosis, and Limp Lobster Syndrome. The research ended in February 2010.
All of this research was published in June 2012. The entire issue of the Journal of Shellfish Research (Volume 31, Number 2) is devoted to epizootic shell disease. It includes the papers describing each of the 15 research projects, a synthesis of the research from the NE Lobster Research Initiative, two other papers: one on the status of the southern NE lobster stock by Howell and a fisherman’s perspective, by Lanny Delinger, the president of the RI Lobstermen’s Association.
As Marta Gomez-Chiarri and J. Stanley Cobb wrote in their Synthesis of Research from the New England Lobster Research Initiative: Lobster Shell Disease, “Most of the data indicate that shell disease is caused by an opportunistic pathogen [a causative agent, such as a bacterium or virus] or pathogens that take advantage of a compromised shell.” Andrei Chistoserdov and other researchers showed two bacterial species: Aquimarina ‘homaria’ and ‘Thalassobius’ appear consistently with shell disease lesions. Experiment after experiment, Gomez-Chiarri and Cobb state, “Provide support to the hypothesis that A. ‘homaria’ is a causative agent of ESD in lobsters.”
Researchers found that lobsters with shell disease have higher levels of the molting hormone than healthy lobsters. These high levels of molting hormone in berried females implied possible problems with reproductive cycles in animals with ESD. “The persistent damage to the shell is somehow signaling the lobsters to prepare for molting,” Castro said.
But after all these years with all those scientists and graduate students studying the causes of ESD from 2007 to the autumn of 2012, although much research has been done and many papers written, scientists still do not have a definitive answer to what causes shell disease
As Castro explained in mid-September 2012, “The trouble is there is more than just the pathogen [a bacteria or virus that causes the disease] at play here. We know there are bacteria in common but we cannot just put the pathogen on the animal and get it sick. The lobster has to be stressed somehow. Therefore, the general stress factor is actually playing a huge role in ‘infectivity.’” That this disease has complex causes make it hard to study.
In other words, although science has not found the causes of ESD, researchers are getting there. They know a lobster has to have something wrong with it—that compromised shell they speak of—for it to develop shell disease. We just have to keep at it. We have to see that the researchers have the funding they need to keep looking for the causes of shell disease so we can put an end to it and the damage it is doing to our vital lobster industry.