Research Illuminates the Role of Disease in Shaping Ocean Health

Over the last 20 years, the Southern New England lobster fishery, an economic staple from New York to Massachusetts for well over a century, has struggled. The collapse is largely attributed to rising water temperatures, but there’s been another culprit lurking in the water since the 1990s — epizootic shell disease, a bacterial infection that causes potentially fatal lesions in infected lobsters.

Shell disease is one of the several maladies that Maya Groner studies. A disease ecologist, and one of Bigelow Laboratory’s newest senior research scientists, Groner uses field surveys, experiments, and mathematical models to understand pathogens that affect marine populations. As warming temperatures become the norm across the world’s oceans and potentially increase vulnerability to these diseases, Groner is working with fisheries managers to better understand their impacts and work toward solutions.

“My interest is in combining different kinds of datasets to understand the underlying drivers of disease and ultimately inform management,” Groner said. “Disease is a natural part of any ecosystem, but if we can understand these diseases, we may be able to figure out ways to reduce their negative effects.”

Recently, Groner published a paper in the ICES Journal of Marine Science on the prevalence of ichthyophoniasis, a widespread disease caused by a fungus-like parasite, in two Pacific herring populations in the Gulf of Alaska. The study, funded by the Exxon Valdez Oil Spill Trustee Council and the North Pacific Research Board, was based on research she began as a scientist with the Prince William Sound Science Center before coming to Bigelow Laboratory.

Pacific herring, like other forage fish species, are prone to large swings in population year-to-year, but it can be challenging to pinpoint the role of disease in those variations without sufficient targeted data. In Prince William Sound, the site of the devastating Exxon Valdez oil spill in 1989, understanding disease dynamics amid a host of ecosystem changes has been particularly challenging.

“It’s been a long time since the oil spill happened, but the herring continued to decline for nearly 30 years,” Groner said, pointing out that 2021 was the first time in decades that scientists saw an increase in the Prince William Sound population. “There’s clearly something else going on, so we’ve been trying to understand disease as a potential contributor.”

Combining disease surveillance data with annual fish surveys from the Alaska Department of Fish and Game, Groner and her colleagues set out to measure the rate of ichthyophoniasis in Prince William Sound from 2007 to 2019. They then compared that with the prevalence of the disease in nearby Sitka Sound, further down the coast where the herring fishery is thriving.

Because ichthyophoniasis is a chronic condition, disease rates are inevitably higher where the population is older, so first the team had to account for the age differences between the two populations. After doing so, they showed that infections have declined in both populations over time, though the disease is still more widespread in Prince William Sound. That’s important for scientists to know as they try to piece together why herring have continued to struggle even as other species have recovered from the oil spill.

The herring research encapsulates Groner’s broader approach to her research, which is all about creatively combining data sources, finding common threads in different environmental systems, and collaborating with fishery stakeholders to understand the impact of disease. Since coming to Bigelow Laboratory, she’s continued that kind of work, both in Alaska, where she’s looking at several pathogens that affect snow crabs, and on the East Coast. She’s recently kicked off a project to understand whether Maine lobster may be vulnerable to shell disease in the future as the Gulf of Maine continues to warm.

“The Gulf of Maine is warming. The Gulf of Alaska is warming. The Bering Sea is losing its sea ice,” she said. “You really can’t look at these diseases out of that context.”

Scientists, she said, have detected a relationship between warmer temperatures and disease prevalence for most marine diseases, including ichthyophoniasis and shell disease. However, more work is needed to understand whether warming is driving disease rates directly, or whether the two things are just correlated in a rapidly changing world. Combining the standard suite of fisheries data with disease and environmental data is necessary to tease apart those relationships and get a complete picture of how marine populations are changing.

“The herring work especially opened my eyes to the value of working with fisheries biologists and managers,” she said. “Disease is almost never included in stock assessments, even though it can be a really important source of variation in populations, and it’s only becoming more so, so the need to combine those datasets is as great as ever.”

Photo 1: Snow crabs that Groner and Postdoctoral Scientist Reyn Yoshioka are examining as part of an experiment on black eye syndrome in the Bering Sea

Photo 2: Groner out in the field in Alaska

Photo 3: Sampling herring during spawning seasons in Sitka, Alaska, with biologists from the Alaska Department of Fish and Game