A Warming Threat to Maine’s Lobsters

The water in the Gulf of Maine is warming rapidly, a change that could bring a once-rare lobster disease further north. 

Published March 31, 2016

In 2012, on the coast of Maine, lobstermen started showing up at Samuel Belknap’s dock with lobsters whose shells were covered in lesions. The shellfish were suffering from “epizootic shell disease,” a mysterious affliction that, in the worst cases, makes it look like “someone took battery acid and poured it on the lobster,” says lobster biologist Kathleen Reardon.

Belknap had grown up around lobsters, working as the skipper of a lobster boat, then as a dock boy, and later as the operator of his family’s dock in Bristol, Maine. The appearance of the disease left him both concerned and intrigued. It’s part of what inspired him to start a PhD program at the University of Maine, where he studies the ways shell disease and climate change may affect the lobster industry.

Right now, shell disease is rare in the Gulf of Maine. Only about one in every 200 lobsters is afflicted. Ultimately, the disease seems to be caused by bacterial communities, most notably the bacterium Aquimarina homaria. But this bacterium is naturally present on the lobsters’ shells, so now the search is on for the disease’s penultimate cause. The running hypothesis is that lobsters become susceptible when they’re stressed and their immune systems are compromised. One major cause of stress? High water temperatures.

Farther south, in the warmer water of Long Island Sound, nearly a third of lobsters have shell disease, a likely factor in the collapse of the lobster fishery industry there in 1999. The specter of mass sickness is making some lobstermen and researchers in Maine, where lobsters make up over 80 percent of the fishing industry and where water temperatures are increasing faster than almost anywhere else in the world, particularly nervous.

The lobster industry in Maine doesn’t appear to be in any immediate danger. In fact, lobster landings for the past several years are at all-time highs. But shell disease prevalence peaked in 2013 at two percent after the warm winter in 2012; this past winter has been similarly warm. Belknap says he wouldn’t be surprised if there is another uptick in shell disease in the coming year, although he’s reticent to make predictions.

But those kinds of predictions are exactly what fisheries managers need, says Jeffrey Maynard, a senior scientist with SymbioSeas. In a new paper, Maynard and his colleagues outline how surveillance and forecasting tools could be developed for lobster shell disease and for several other seemingly temperature-dependent diseases, including those that afflict corals, oysters, and sea stars.

Temperature monitoring can take many forms, from near real-time monitoring to long-term climate forecasts. Real-time or seasonal monitoring can give scientists and resource managers a heads-up if average monthly water temperature maximums approach an important threshold (for lobster shellfish disease: 12 °C). Looking further into the future, climate models can help predict if shell disease might eventually wreak the same kind of havoc in Maine as it did farther south.

Getting an early warning of impending trouble would be invaluable. “We’ve seen what happened in southern New England,” says Reardon, who works with the Maine Department of Marine Resources. No one was really looking for shell disease down there, she says, “and then all of a sudden, they were having lobsters dying.”

In the short term, lobstermen who know that a warmer winter is coming could change their business plans for the season and prepare for a lower catch, says Reardon. And on a longer timescale, temperature monitoring could add urgency to ongoing efforts to diversify the fisheries industry in Maine, says Belknap. And if other factors besides temperature, like pollution, do significantly influence shell disease, then new regulations could be enacted.

Current research is helping pin down the causes of shell disease and even points to possible solutions. Jeffrey Shields, an epidemiologist at the Virginia Institute of Marine Science and a co-author on the new paper, just wrapped up an experiment in which he exposed healthy and diseased lobsters to different water temperatures. At lower temperatures, diseased lobsters molted and healed. But at the higher temperatures, “we had clear progression of the disease,” Shields says. However, the disease didn’t appear in healthy lobsters kept at higher temperatures, suggesting that other factors, such as pollution, may also contribute to the disease. Other possibilities, like the use of probiotics, are also being explored.

Back at the Belknap family dock, lobster fishermen seem far less concerned with shell disease than they were in 2012 and 2013, says Belknap. “When things are good, people don’t see looming threats on the horizon.” But there are risks to being complacent.

When an outbreak does occur, there is little funding available for tracking or responding to the disease. A bill sitting in Congress could change that. The Marine Disease Emergency Act, says Maynard, “would provide much-needed resources when outbreaks are declared to be emergencies.” Though, as the bill is currently written, it wouldn’t provide funding for research before an outbreak occurs.

Maynard and his colleagues predict that in the next 20 years, bottom water temperatures in large swaths of the Gulf of Maine could cross the 12 °C threshold. If that happens, it won’t bode well for the lobster industry. But with early warning and active research on shell disease, scientists may be able to ensure that we can continue to enjoy Maine lobster rolls for decades to come.