Alevin salmon in experimental fish tanks. (Credit: Michelle Ou)
Ocean acidification is a big topic of conversation right now, and for good reason. The uptake in carbon dioxide is affecting the survival of marine life and potentially devastating habitats. Freshwater acidification, however, is largely unexplored, yet still just as challenging for wildlife.
According to Michelle Ou, who currently works for the ministry of environment in the Canadian province of British Columbia, freshwater has large variations in CO2 levels depending on time of year and location, making it more difficult to study its effects. She led a study while a graduate student at the University of British Columbia that looked at the effects of freshwater acidification on pink salmon.
The study, published in the journal Nature Climate Change, began in Vancouver. The team reared the salmon in the Quinsam River Hatchery of the Campbell River on Vancouver Island. Then the salmon were taken to the lab at the University of British Columbia and exposed to different levels of CO2. Some were raised in waters with current CO2 levels and others were raised in tanks with CO2 levels all the way up to 2,000 parts per million. After 10 weeks, they were transferred to saltwater tanks where they were observed.
Scientists found that the fish that were exposed to higher levels of CO2 were smaller and their sense of smell was largely impaired.
According to Ou, a salmon’s sense of smell is crucial for survival. Firstly, because their smell leads to alarm cues, making it less likely that they will sense danger and change direction to avoid predation. This is important because the salmon are already smaller, which makes them more susceptible to predation, so not being able to defend themselves by smell largely affects their survival.
Secondly, salmon can smell amino acids in the water to give them the ability to find their way back to spawning grounds. Amino acids serve as a kind of fingerprint, said Ou, which helps them determine how to get back to their home waters. But, after exposed to the higher levels of CO2, their ability to do so was impaired.
According to the study’s authors, pink salmon are a “keystone species in marine, freshwater and terrestrial ecosystems because of their role in supporting food webs.” This means that if salmon are endangered by acidification, entire ecosystems are in jeopardy as well.
Ou said they did not factor a salmon’s ability to adapt to higher levels of CO2 into the study. They also didn’t look for more resilient or resistant study subjects. However, after seeing the effects that acidification has on the fish, the team has some concerns for this important species. The researchers encourage mitigation as a result of their study, especially because many rivers across the world are already experiencing fluctuating and higher levels of CO2.
“When you think about emission of CO2 into the atmosphere, that is the biggest driver. I think that’s a problem not just with this study or salmon or fish or even ocean acidification, it’s a big problem in general. So it’s more about how we can reduce that,” said Ou. “You can select for individuals who are more resistant and resilient to increases in temperature and CO2, but it’s difficult to think about how we are actually going to approach that.”
Ou hopes to expand on the research by looking more into salmon’s impaired sense of smell, because it is so crucial to their survival. She also mentioned that salmon are an indicator species on the Canadian west coast, so salmon can be used to tell whether ecosystems there are healthy or not.
Top image: Alevin salmon in experimental fish tanks. (Credit: Michelle Ou)