UMaine researchers find rising ocean temperatures, acidification worsen immune response, physiology in lobsters  

Rising ocean temperatures and acidification, which results from decreasing pH levels, can increase adolescent lobsters’ vulnerability to disease and impact their physiology, according to University of Maine scientists.

Amalia Harrington studied the individual and combined effects of increased ocean acidification and warmth on adolescent, female American lobsters as a postdoctoral researcher at UMaine. Faculty from the Aquaculture Research Institute (ARI) collaborated with her on the study, including Heather Hamlin, an associate professor of aquaculture and marine sciences; Deborah Bouchard, ARI director; and Robert Harrington, an ARI research associate.

The team found that these lobsters could face weakened immune responses and reduced thermal tolerance by the end of the century if oceans continue to warm and acidify. The researchers published their findings in the Journal of Crustacean Biology. 

The study, the first to look at the combined effects of ocean warming and acidification on the physiology and immune response of adolescent, female American lobsters, was funded by the National Oceanic and Atmospheric Administration and National Science Foundation. 

“Our work is unique because we focused on understanding both the individual and interactive effects of two important environmental stressors, warming and acidification, on lobsters that are in transition to adulthood,” says Harrington, now a marine extension associate with Maine Sea Grant. “Changes in their physiology to respond to these stressors could result in trade-offs with other critical biological processes, potentially impacting their success as adult lobsters in this important fishery.” 

The researchers conducted an environmental-stressor experiment in which they exposed lobsters to what ocean water temperatures and pH levels are predicted to reach by the end of the century, if greenhouse gas emissions continue rising. Four groups of lobsters experienced different conditions so the UMaine team could ascertain the individual and combined effects of both stressors on lobster biology. The first group was exposed to typical Maine summer conditions to serve as a control scenario. The second group was exposed to only elevated temperatures to mimic just a warming scenario. The third group was only exposed to reduced pH levels to replicate an acidified environment. The final group was exposed to both warming and acidification. 

The adolescent lobsters experienced the environmental stressors for 42 days, after which the researchers tracked their capacity to deal with an additional stressful event by measuring heart rate during a temperature ramping experiment. The team monitored heart function as they consecutively increased temperatures during the two-hour experiment. 

Researchers found that lobsters exposed to both predicted end-century temperatures and pH exhibited a reduced ability to maintain heart function during the ramp experiment, unlike the crustaceans subjected to only one of the stressors or current summer conditions. The finding suggests that the combined effects of warming and acidification could reduce physiological performance in adolescent American lobsters and inhibit their capability to deal with other stressors or maintain proper biological functions.

Following the environmental-stressor experiment, the UMaine scientists measured the lobsters’ hemocytes, or blood cells, and tested their ability to fight off disease to understand how warming and acidification might influence their immune response. Lobsters pre-exposed to warmer temperatures, regardless of pH, had significantly fewer hemocytes, which help fight disease, compared to lobsters that experienced current ocean temperature treatments, suggesting that they might possess a weaker immune response. 

The group then conducted a 21-day pathogen challenge with the bacteria that can cause Gaffkemia. Known as a wasting disease, Gaffkemia can result in reduced appetite and lethargy, as well as limb loss and death in American lobsters. They found that lobsters preexposed to warmer temperatures, regardless of pH, could die up to five days sooner than lobsters exposed to current summer temperatures. Almost twice as many lobsters exposed to both warming and acidification lost at least one claw compared to the lobster groups exposed to other conditions, which could increase the risk of death by a secondary infection. 

“While this in no way implies our lobster populations are on the verge of collapse, it does suggest we need to continue to be vigilant in surveying our lobsters for disease outbreaks, and the possibility of other stressors,” Hamlin says. 

Contact: Marcus Wolf, marcus.wolf@maine.edu