Pink salmon may be at risk in the future from the effects of climate change-related acidification of their freshwater habitats, concludes a paper published online this week in Nature Climate Change. Ocean acidification, caused by rising levels of CO2, negatively affects marine species and is expected to cause widespread changes in saltwater ecosystems over coming decades. However, the potential impacts of acidification on freshwater ecosystems have attracted less attention.
Salmon start life in freshwater, but spend most of their juvenile and adult lives out at sea, before returning to the rivers and streams they were born in to spawn. Pink salmon are the most abundant salmon species in the northern Pacific and contribute to the productivity and function of coastal ecosystems. They are also of considerable cultural significance to the northern Pacific aboriginal communities that are supported by them.
Michelle Ou, Colin Brauner and colleagues reared pink salmon embryos and juveniles, for 10 weeks, at current and projected future CO2 levels and then transferred them to seawater. They found that hatchlings and juvenile pink salmon exposed to elevated CO2 levels exhibited reduced growth and altered metabolism, both during freshwater development and following seawater entry. They also found that these salmon spent significantly more time in water containing alarm cues and near a novel object, suggesting that elevated CO2 may reduce anxiety in pink salmon fry. This, combined with their smaller size, could make them more susceptible to predation.
The findings suggest that, unless populations can adapt, increases in CO2 in fresh water could detrimentally affect the ability of young pink salmon to migrate downstream, as well as their survival in the first part of the marine life stage.
In an accompanying News & Views, Philip Munday writes, “Any effects of elevated CO2 on the growth and survival of juvenile salmon could [therefore] have far-reaching ecological, economic and social consequences.”