Race on to understand lobster diseases

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ROCKPORT – Maine’s lobsters thus far have dodged the disease outbreaks that have decimated the Long Island Sound fishery and diminished harvests in Massachusetts Bay in recent years.

But the “perfect storm” of symptoms that struck to our south could pose risks to the Gulf of Maine’s multimillion-dollar industry unless they are better understood, a panel of researchers told fishermen at a daylong lobster health symposium at the annual Fisherman’s Forum on Saturday.

“Don’t breathe too big a sigh of relief yet,” said Jan Factor of Purchase College, State University of New York.

Zoologists have been publishing papers about lobsters since the 1890s, yet the pricey crustaceans are still far more mysterious to science than a typical household pet, he said.

After the 1999 lobster die-off in Western Long Island Sound, teams of researchers worldwide began searching for an answer. Laboratories have since identified two distinct diseases that struck the fishery in the late ’90s – limp lobster syndrome, which struck the western portion of the sound, and shell disease, which infested the eastern sound and has been moving steadily north and east ever since.

Charles O’Kelly, a researcher at the Bigelow Laboratory for Ocean Sciences in West Boothbay Harbor, likened Long Island Sound in the late ’90s to an overheated, overcrowded room into which a flu bug was introduced.

“If I’m a physician, I’ve got warning bells going off in my head,” he said.

Lobsters had reached record population levels when, in the summer of 1999, the triple punch of drought, heat and tropical storms hit Western Long Island Sound, creating an environment in which both the high temperature and the ocean bottom’s low oxygen content were stressful to lobsters.

Local fishermen had believed (and many still do) that a massive pesticide application on land, in response to a West Nile virus outbreak, was the cause of lobster deaths in 1999. However, laboratory studies of the pesticides involved suggested that while the pesticides could kill lobsters, which are closely related to insects, the amounts that reached Long Island Sound would not “alone” have been enough to spark the die-off.

Factor believes that, like humans, lobsters suffer under stress.

In lab experiments in which lobsters were deprived of oxygen while exposed to heat and harmful chemicals that naturally arise in undersea sediments in the absence of oxygen (all characteristics of Long Island Sound in 1999), the animals died in just a few days.

Introduce additional stressors of low levels of pesticides and disease, and you have lobster carnage, Factor said.

Lower levels of stress can cause changes in lobster hormones, affecting molting and breeding behavior, as well as their immune systems, he said.

“We have to think about stress piled upon stress piled upon stress,” Factor said. “Like us, these lobsters are not just exposed to one problem at a time.”

That stress may prove to be a factor, if not the answer, to why tiny organisms that have always been a part of the marine environment suddenly started killing lobsters over the past decade.

Limp lobster syndrome, which destroyed the Western Long Island Sound fishery, has been linked to an amoeba not previously known to fisheries scientists.

“People were thinking that we had basically brought the bug from Mars,” O’Kelly said.

To their surprise, researchers learned that the mysterious amoeba lives throughout the marine environment, on rocks, and even the backs of lobster shells, where it grazes on bacteria.

“There’s a whole tiny little forest on the back of the shell … and most of [the organisms] are new to science” he said.

Over time, scientists learned that this particular amoeba has been linked to similar diseases in salmon, urchins and crabs. Why the amoeba changes its behavior and invades other organisms remains a mystery.

“We just don’t know what makes an amoeba that normally sits on seaweed and eats bacteria decide that it wants to go to a restaurant and eat lobster,” O’Kelly said.

Epizootic shell disease, the more widespread but less frequently fatal problem that has traveled north into Massachusetts Bay, is also caused by a long-overlooked organism – bacteria that can infect the shell, eating through it in a matter of weeks. While the bacteria don’t infect a lobster’s meat, they make the animal less healthy and far less marketable.

“As you know, better than I do, no one wants to buy a scabby little animal,” O’Kelly said.

Kathleen Castro has been studying shell disease at Rhode Island Sea Grant, where she serves as assistant director. The disease first appeared in her region in 1996, after a major oil spill that stressed the marine environment. Today, about a third of the lobster population, of all ages and both genders, is believed to be infected. When infected lobsters molt, their new shells can become diseased in just a week.

“Molting does not cure the problem,” Castro said.

While shell disease rarely kills lobsters, natural mortality rates have been growing in recent years, because diseased lobster, to put it simply, act sick. They hide, don’t go exploring and may not be eating or breeding, she said.

To ensure a future for the region’s lobster industry, all of the factors that cause illness and stress must be better understood, said Rick Cawthorn, who conducts parasite research at the Atlantic Veterinary College of the University of Prince Edward Island.

We need to answer “one simple question that isn’t very simple: What constitutes a healthy lobster?” he said.