Lobster Chronicle
A hunt for the cause of a new disease that threatens N.H.'s most important commercial fishery.
Lots of people may have lobster leftovers in the fridge. Not Elise Sullivan: She has lobster scrapings. “We have a huge freezer full of bacteria that has come off lobsters, and we’re getting more all the time,” says the marine microbiologist matter-of-factly—further evidence that you should always approach a scientist’s kitchen with care.
But Sullivan, an assistant professor in the Department of Microbiology, isn’t on the hunt for a new sushi variant. With post-doc Kim Nelson, she is trying to pin down why an increasing number of lobsters have holes in their shells, victims of a disease that lowers their value to fishermen and may have contributed to past population crashes in Long Island Sound. The disease has reached epidemic proportions south of Cape Cod and seems to be moving north.
“There has always been some evidence of shell disease on a seasonal basis in New Hampshire waters and the Gulf of Maine, but it has shown up in a higher percentage over the last couple of years, and not just in warmer months,” says John Nelson, chief of marine fisheries at New Hampshire Fish and Game. “It’s probably less than five percent right now, but we’re trying to be proactive, to find answers early.”
For such a potentially big problem, lobster shell disease starts very small. “If you weren’t trained to see the pits, you wouldn’t see them in the initial phases,” says Sullivan. “They are maybe one millimeter in size, but slowly get deeper and wider and start merging together and become blatantly obvious.”
While disease doesn’t necessarily kill the lobsters, it does make them susceptible to other ailments. And although it doesn’t seem to effect the meat, no restaurant or supermarket will buy a pitted lobster.
By process of elimination, Sullivan believes the condition is caused by bacteria that live on lobster shells. But which ones?
“Surfaces are wonderful places in a marine environment for bacteria to live; one swab off a shell, you can easily get 15-20 organisms to culture,” says Sullivan.
Hence the freezer full of specimens: more than 100 different isolates for Sullivan’s lab to study. She is screening the DNA to get the bacteria’s molecular “fingerprints,” and is in the process of setting up techniques to examine the genes of an entire community of bacteria at one time. By comparing microbial populations on healthy and diseased shells, she hopes to find a culprit.
“There’s a lot of bacteria to pick through to find a pattern—it’s not going to be trivial to pick it out,” she says ruefully. “We still don’t know whether the problem is from some new organism that’s more pathogenic, or one that’s part of the shell’s normal flora, but for some reason, a diseased lobster’s immune system is weakened.”
Sullivan and Nelson are also trying to answer some very basic questions about how to handle the outbreak. “If a lobsterman pulls up a diseased lobster, what should he do with it? Put it in a tank? Kill it? Throw it back?” Sullivan queries. To answer these questions, they are looking at how the infection spreads by placing diseased lobsters and healthy lobsters in a tank separated by netting, to see if the disease can be transmitted through water without direct contact.
Finding the culprit won’t be easy, and devising a response will be harder still. “You’re not going to dump antibiotics into the ocean,” notes Sullivan. ”But when it comes to the most important commercial fishery left in the state— almost two million pounds of lobsters were landed in New Hampshire last year—finding answers early is critical.”
—David Brooks
