Experiments Help Test Lobsters’ Vulnerability to Disease

In 1997, the lobster catch in southern New England hit 22 million pounds. By 2013, it was down almost 90%. The crash of that fishery in the late 1990s and early 2000s was environmentally and economically devastating, and warming was largely to blame. It made it harder for adult lobsters to reproduce and young ones to thrive. It also enabled an emerging disease to run rampant.

Epizootic shell disease (ESD) is caused by an imbalance, or dysbiosis, in naturally-occurring bacteria that live on lobster shells. Even mild cases can cause degradation in the shell that makes the lobsters, in essence, too ugly to sell, but if it becomes severe enough, the disease can also be fatal.

Though the Gulf of Maine is warming rapidly, its temperatures aren’t yet as high as southern New England; in fact, the somewhat warmer waters may actually be contributing to the industry’s recent boom.

Yet, scientists worry a tipping point could be coming.

Funded by Sea Grant’s American Lobster Initiative, researchers from Bigelow Laboratory for Ocean Sciences and the Maine Department of Marine Resources are partnering to investigate how warming temperatures makes Gulf of Maine lobsters vulnerable to disease like ESD, bringing together managers, scientists, and fishermen to help ensure the future of the fishery.

“This type of collaboration, where managers, disease ecologists, and modelers contribute to designing and conducting research, is the future of the field,” said Senior Research Scientist Maya Groner, who leads the project. “We hope that by co-developing this project, and then working for fishermen to understand their perceptions and concerns, we can produce management-relevant research and build trust with this community as they adapt to changing conditions.”

Postdoctoral Scientist Melissa Rocker describes ESD as an “opportunistic disease,” which makes it critical to understand how different lobster populations respond to environmental stress. Looking backwards, she says, will help them understand how the disease could progress in the future.

One of the big concerns the researchers have is the growing mismatch in timing between when the disease appears and the lobster’s molting cycle, which seems to be changing in a warming world. Adult male lobsters, for example, molt annually, and if they molt shortly after getting the disease, they’ll be fine. But if they molt, say, in early spring, that leaves all summer to acquire the disease — and all winter for it to progress. It’s even more concerning for adult females that typically only molt every other year. That not only leaves more time for them to get sick but also means that they may waste valuable energy fighting off the disease.

“Molting is a stressful event as it is,” Rocker said. “We think of a no-disease lobster as a healthy lobster, but if they’re spending all their energy molting to get rid of the disease, they may not have the energy they need for growth and reproduction.”

Last year, Rocker worked with several summer interns and Research Associate Kirsten Johnston to run a large-scale experiment to see what effect temperature has on the disease and its spread — and whether Maine lobsters respond differently than their southern counterparts.

Working with Maine DMR, the Division of Marine Fisheries in Massachusetts, and Dominion Energy in Connecticut, the team collected 62 healthy lobsters from across the three states. Half were kept in cooler water — around 55 degrees, which is the temperature at which the disease can manifest. The other half were kept closer to 68 degrees, temperatures that are now commonplace in southern New England where the disease is widespread.

Over the course of the 140-day experiment, almost every lobster in the warm water developed some signs of disease. Surprisingly, they found that ESD was more common, and progressed more quickly, in the Maine lobsters. Yet, those individuals largely all molted and reset with healthy shells by the experiment’s end.

“If you had only taken beginning and end photographs, you would have thought the Maine lobsters were fine when in fact, they did get the disease; they just molted out of it, which may have used up valuable energy resources” Rocker said. “That highlights why regular monitoring is so important for a disease like this.”

The team, which includes researchers Reyn Yoshioka and Nick Record as well, are also using fishery observer data from DMR and DMF and various epidemiological methods to better estimate how the disease progresses, how prevalent it is, and both mortality and molting rates. They’re using that data to create predictive models for how the population could respond in the future, especially if temperatures continue to rise.

For this current project, DMR has been an invaluable partner, including hosting the experiment in their facilities. But Rocker said she hopes that, in the future, Bigelow Laboratory will have resources to pursue this kind of work in-house. To that end, she and Groner’s whole lab are working to upgrade the Bigelow Laboratory seawater suite. Part of that upgrade is creating a quarantine system with advanced sterilization processes for water outflow to enable more research on marine diseases.

“Doing this experiment at DMR was great from a collaboration standpoint, but the upgrade and quarantine system is super important to allow us the flexibility to do more of this kind of science in the future,” Rocker said. “Our institute prides itself on working on the ‘invisible’ parts of the ocean, and viruses, bacteria, and diseases are an important part of that world.”

Photo Captions:

Photo 1: Postdoctoral scientist Melissa Rocker poses with a lobster that is part of her ESD experiment (Credit: Catie Cleveland/College of Charleston).

Photo 2: A lobster with some evidence of the pitting and spots emblematic of ESD (Credit: Catie Cleveland/College of Charleston).

Video: Rocker lifts up one of the tanks of her lobster experiment at DMR’s facility (Credit: Melissa Rocker).