After exposing adult krill to ocean acidification levels that are predicted to occur over the next century, researchers at the University of Tasmania were surprised to find that they were largely unaffected. The study contradicts the findings of previous research that suggest Antarctic krill will be vulnerable to acidification during certain stages of life.
Study lead author and PhD student Jess Ericson said the long-term lab analysis was the first of its kind.
“Our study found that adult krill are able to survive, grow and mature when exposed for up to one year to ocean acidification levels that can be expected this century,” said Ericson.
“We reared adult krill in laboratory tanks for 46-weeks in seawater with a range of pH levels, including those in the present day, levels predicted within 100-300 years, and up to an extreme level.”
“We measured a suite of physiological and biochemical variables to investigate how future ocean acidification may affect the survival, size, lipid stores, reproduction, metabolism and extracellular fluid of krill.”
Ericson said the results showed that the physiological processes of the krill were not hindered by the pH levels that are expected over the coming century.
“The adult krill we monitored were able to actively maintain the acid-base balance of their body fluids as seawater pH levels decreased, thereby enhancing their resilience to ocean acidification.”
According to Ericson, the findings are important because krill serve as a critical link in the Antarctic food chain.
“Ocean acidification caused by anthropogenic carbon dioxide emissions is predicted to occur most rapidly at high latitudes, such as in the Southern Ocean.”
“Krill are a major prey item for marine mammals and seabirds, and any decrease in their abundance as a result of ocean acidification could result in significant changes in the Southern Ocean and Antarctic ecosystem.”
Ericson explained that increasing ocean acidity is known to have negative effects on a range of marine invertebrates, causing issues such as the dissolution of calcium carbonate shells, delayed growth, increased mortality, and delayed reproduction. There has also been evidence that acidification causes abnormalities in offspring.
“Our finding that adult Antarctic krill appear resilient to such conditions is therefore an interesting and significant result,” she said. “However, the persistence of krill in a changing ocean will also depend on how they respond to ocean acidification in synergy with other stressors, such as ocean warming and decreases in sea ice extent.”
The study is published in the journal Communications Biology.