Antarctica’s highly specialized wildlife is suffering from climate change in a variety of ways. Rising water temperatures, even at the seafloor, less saline water due to melting glaciers, and other factors are putting fish and other marine animals under enormous stress, increasing their susceptibility to disease. Fish of the suborder Notothenioidei (Antarctic fish) are already severely affected. A research team led by the University of Oregon observed an outbreak of a skin disease in Antarctic fish along the western Antarctic Peninsula that is triggered by parasites and forms tumors. In their study, now published in the journal iScience, the researchers cite climate change as a possible cause.
For about ten years, John Postlethwait and Thomas Desvignes, biologists at the University of Oregon, have been studying Antarctic fish west of the Antarctic Peninsula. During a research trip in 2018, they observed in a small fjord that a large number of the fish were affected by skin tumors.
“As soon as we got the first trawl back on deck, we realized that one species was really abundant, and a lot of them had big tumors,” Desvignes said. “When we saw that, we immediately realized we had to do something.”
The team collected samples from both sick and healthy fish. Virologists and pathologists later found out in the lab that the tumors were caused by a parasitic disease. “Very little is known about diseases associated with these animals,” said Arvind Varsani, an Arizona State University virologist and co-author of the study.
Genetic analysis of the tumors revealed that the disease is caused by single-cell parasites known as X cells. However, X-cell disease has been little studied. The disease has been found sporadically in wild stocks of cod, salmon, halibut and other fish species in Iceland and Norway, but it is not known exactly how it is transmitted. In addition, the team found that the parasites belonged to a different genus than other parasites detected in previous cases of X-cell disease.
The tumors were particularly common behind the head and near the anal opening, suggesting that the infections were food-related. The tumors affect the fish in such a way that the infected animals had a lower weight than the healthy ones.
The scale of the outbreak is unprecedented – something the team and other researchers not involved in the study had never seen before in Antarctica. Pinpointing the cause of the clustered occurrence is difficult. However, Antarctic ecosystems are particularly vulnerable to the effects of climate change and are currently experiencing exceptionally rapid changes. For example, meltwater input from glaciers is causing ocean temperatures near them to rise and the salinity of seawater to drop. The water above the seafloor, where the notothenioids live, is warming particularly rapidly and becoming less saline.
The changes in the ecosystem could make living conditions more difficult and put pressure on the fish, making them more susceptible to disease, suspects Thomas Desvignes, lead scientist of the research expedition and lead author of the study. However, climate change could also affect the parasite’s life cycle, perhaps allowing it to spread and infect fish more effectively.
Other reasons unrelated to climate change could also explain the outbreak, but the team needs more data to draw more accurate conclusions. “Maybe the parasite has a long life cycle and only triggers disease every once in a while, and we may have happened to be there when that happened,” Desvignes says.
“We’re preparing project proposals to go there again and study this specific outbreak, how it evolved since 2018, and explore adjacent areas to try to see whether we can detect the pathogen elsewhere and in other species,” Desvignes said.
Julia Hager, PolarJournal