Shell disease concerns lobster fishery

October 2, 2008 at 6:58 pm Leave a comment

Remember when Dustin Hoffman’s father-in-law whispered one word into his ear, “plastics” in a pivotal scene in “The Graduate”?

Well, University of Connecticut molecular cell biologist Hans Laufer is whispering the same word as a potential cause for lobster epizooticshell disease.

Not quite as dramatic an effect, but enough to catch the attention of those who love lobsters. Laufer has been coming to the Marine Biological Laboratory in Woods Hole since he first arrived as a student in 1956. He’s also taught there and currently is a summer researcher.
Epizootic shell disease first appeared in Long Island Sound in the 1990s and spread up the coast to Cape Cod by 2000. Infections peaked at 28 percent of lobsters caught in Buzzards Bay in 2003 and have since tailed off. Cape Cod Bay infections hit 11 percent of the lobsters in 2000 and 2001. The disease has been rare on the Outer Cape.

“It’s here but whether it’s clearly a problem – I’d say not yet,” noted Nick Hyora, a Chatham lobsterman and skipper of the Wildwood. “But that’s subject to change for sure. Today I didn’t see hardly any. It’s a very small percentage here. But it could easily become a concern.”
Closer to the Cape Cod Canal lobstermen have been more concerned.

“In Buzzards Bay they had it bad for a few years. Right now it’s not a problem. I don’t think I’ve seen shell disease on a lobster in the past month,” said David Casoni, who lobsters out of Sandwich. “Part of the reason is when they molt they lose it. It’s gone. Shell disease is not passed from lobster to lobster.”
Temperature, Casoni pointed out, has been linked to the disease and may explain the year-to-yearfluctuations. “After a warmer winter you generally see more,” he said. “A cold, cold winter – less shell disease.

There are statistics on that. We get more in the spring than any other time. This past spring we had probably 5 percent, that’s a lot. That is identified shell disease. When you pick up a lobster it may have a little pit on the claw, that’s actual shell disease but it’s not the real ugly looking shell.”

Robert Glenn and Tracy Pugh of the Division of Marine Fisheries published a study in the Journal of Crustacean Biology in 2006 linking the disease to water temperature but in that case they drew the connection to summer days with water temperatures over 20 degrees centigrade. It was their belief that the disease would then show up the following year.

Laufer also believes water temperatures are critical to the incidence of shell disease but they aren’t the cause.

“We found these alkylphenols and think they come fromplastic breakdown and also detergents,” Laufer summarized. “They look very similar to the amino acid tyrosine. That is also an alkylphenol and from our experiments it looks like these plastics interfere with tyrosine incorporation which means the shell doesn’t get quite as hard as it normally does.”

The lobster’s hard shell, or exoskeleton, protects it from more than larger predators.

“That means it’s more susceptible to microbial invasion, which is what shell disease is,” Laufer noted. Shell disease doesn’t kill the lobsters, except in more extreme cases but they wind up with black-pitted spots and are too unattractive for sale to consumers. The meat is still good so their fate is in lobster salad.

“Dealers will buy all the lobsters that come in. Anybody can cook them and take the meat out, it’s still good,” Casoni noted. “We were more concerned that we’d see a huge increase in lobsters with shell disease. Then there would be an economic impact because dealers are not going to cook up everything you bring in.”

The problem, disease-wise, is that the trigger for the disease remains a mystery.

“The problem was no one was able to show the particular microbe leading to the disease, no one has been able to induce the disease,” Laufer said. “No one has been able to show any cause.” Thus he suspected it wasn’t a single disease causing organism but something else.

“In the meantime we’d done biochemical trials and they support the hypothesis,” Laufer explained. “We were using radioactive tyrosine and measuring its incorporation during shell formation and they (the alkylphenols) compete very effectively for sites that seem to be cross-binding proteins.” The trials were done over the past summer at the MBL.

There are alkylphenols in lobsters. Laufer found them when he was looking for something else back in the 1990s. At the time, people blamed shell disease on mosquito spraying and when Laufer sought pesticides in lobster tissue he found alkylphenols instead.

“I was startled to find we were the first ones to report this stuff in the lab,” he marveled. “Humans are contaminated with these, close to 95 percent of them are.”

Alkylphenols are in hard plastics, such as baby bottles, and that has landed them in the news. Canada plans to ban bisphenol A from baby bottles on evidence that it disrupts hormonal function. They’re also in DVDs, the linings of food cans, eye-glasses and many other products.

“They don’t seem to break down readily and sewerage treatment plants don’t eliminate them either,” Laufer noted. “We certainly can detect them in sediments and they are probably in other animals the lobsters are eating.”

Theaverage concentration in lobster tissue is one nanogram per milliliter but on rare occasions that can rise to one microgram.

But there isn’t a one-to-one relationship between the plastics and the disease.

“We’ve gotten samples from offshore deepwater (1,000 feet or more) animals and they are much less infected but we find some animals that are carrying eggs and the eggs are infected much more heavily,” Laufer noted. “So they are migrating offshore and once they are in clean water they get cleaned up but the embryo in the shell doesn’t clean up because it has the hard egg shell on.”

All this jibes with the concept that the lobsters pick up the plastics and the disease when they drift into shallow water where the chemicals are more prevalent, near shore. But it doesn’t explain why relatively polluted waters in Boston HarboHarbor harbor little disease while the Elizabeth Islands were a designated hot spot.

“The most heavily polluted area is near New York City and shell disease is not that common there,” Laufer conceded. “So we don’t understand everything about this process. On the other hand, the lobster population is going down and these (alkylphenols) have hormonal activity. They could be affecting the development of young lobsters and larvae.”

Laufer agrees with other scientists that water temperature appears to play a key role.

“Part of the problem is global warming,” he postulated. “When lobsters warm up they become stressed and bacteria grows faster in warm water than cold water. Bacteria contribute to shell disease.”

We are actually near the southern end of the inshore lobster population.

“Long Island Sound is the southern extent of lobster range except for deep water,” Laufer pointed out. “So they could be very susceptible in Long Island Sound as cold water animals.”

Buzzards Bay is also shallow and warm.

“They are doing fine in Maine,” Laufer noted. “But this is just a surmise.”

By Richard Eldred
Harwich Oracle


Entry filed under: Natural Waterfront, Region. Tags: , , , , .

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