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article imageResearch reveals link between global warming and lobster disease

By Karen Graham     Aug 21, 2018 in Science
New findings reveal that earlier springs and hotter summers in the northeastern U.S. are making resident lobsters increasingly susceptible to epizootic shell disease, depleting the population and impacting the local lobster fishery.
New research has found that coastal waters along the northeastern United States are continuing to warm, with bottom temperatures in Long Island Sound increasing on average 0.7 F per decade over the last 40 years. Resident lobsters are becoming increasingly susceptible to epizootic shell disease, a condition that has depleted the southern New England population and severely impacted the local lobster fishery.
The research, funded by NOAA's Saltonstall-Kennedy Program, was a collaboration between William & Mary's Virginia Institute of Marine Science and Dominion Energy's Millstone Environmental Laboratory.. The research was led by Maya Groner, then a postdoctoral associate, of VIMS.
The study, published in the journal The American Naturalist on August 16, 2018, suggests that the increased prevalence of shell disease in area lobsters stems from two factors -- an earlier onset of warmth-induced spring molting, and hotter summers.
American lobster  Homarus americanus - larva  stage V
American lobster, Homarus americanus - larva, stage V
Fisheries and Oceans Canada, Jean-François St-Pierre
"We used the lab's mark-recapture dataset, now going on 37 years, to investigate relationships between temperature, molting phenology, and ESD [epizootic shell disease]," says Groner, currently a research ecologist at the Prince William Sound Science Center in Alaska.
Phenology refers to the study of how plant and animal life is affected by seasonal changes. "Our work shows that temperature increases due to climate change have caused a phenological shift in the molting patterns of lobsters, making them more susceptible to the disease," Groner said.
The study focused on male and juvenile American lobsters (Homarus americanus) because female lobsters have a different molting pattern, usually molting every two years in the region.
This drooping lobster is missing limbs and painted with dark spots  the tell-tale signs of shell dis...
This drooping lobster is missing limbs and painted with dark spots, the tell-tale signs of shell disease.
(Credit: Joseph Caputo/MBL)
What is epizootic shell disease?
Basically, epizootic shell disease is a bacterial infection which causes black lesions on the lobsters' dorsal carapaces, reducing their saleability and sometimes killing the lobsters. The bacterial populations that normally inhabit the surface of a lobster's carapace change and begin consuming the cuticle, causing it to erode.
Typically, the bacteria associated with the lesions are rod­shaped, chitinolytic, and Gram ­negative. The increased prevalence of the disease has now been linked to the increasing water temperatures, and previous studies have found the mortality due to epizootic shell disease can be as high as 70 percent in diseased lobsters.
In the current study, it was found that when a diseased lobster molts, discarding and replacing its shell in order to grow, it essentially sets the disease clock back to zero. So when spring warmth arrives, this creates a seasonal trigger for molting, However, as global warming pushes the spring season to occur earlier, lobsters also molt earlier in the year, giving the disease a jumpstart on its progression into and through the summer months.
Southern New England lobstermen are dealing with dwindling stocks because the lobster population has...
Southern New England lobstermen are dealing with dwindling stocks because the lobster population has migrated north.
The Culinary Institute of America
It was found that for every 1.8 F increase in the average May bottom-water temperature, lobsters molted about six days earlier in spring and that disease prevalence in October correlates even more strongly with summer heat. In years with both warm springs and warm summers, the disease could exceed 80 percent.
"Recent increases in the prevalence of ESD in the Gulf of Maine—home to the largest lobster stock in the US—have raised concerns that the disease is expanding northward," said co-author Jeff Shields, also with VIMS. "If summer temperatures in the Gulf reach levels conducive to ESD within the next few decades—as expected under 'business as usual' climate projections—we're concerned that it will lead to earlier molting in the spring and less molting during the summer when lobsters are most susceptible to the disease."
More about Lobsters, northeast US, epizootic shell disease, disease prevalence, molting