One of the many effects of climate change and rising carbon dioxide levels is the acidification of ocean habitats: Marine creatures with shells appear to be dissolving, sharks won’t be able to hunt as well, and sea snails are shrinking. Even though freshwater fish make up 40% of all fishes, we know less about the effects of acidification on freshwater habitats than saltwater ecosystems. Well, according to a new Nature Climate Change study, pink salmon is at risk. Those exposed to elevated CO2 levels early in life grow up smaller and may be less likely to survive.
Salmon start their lives in freshwater rivers and streams, and then they spend most of their juvenile and adults lives out at sea before returning to spawn. Pink or humpback salmon (Oncorhynchus gorbuscha) are the most abundant salmon species in the northern Pacific. They play key roles in the productivity and function of their coastal ecosystems, and because they enter the ocean at the smallest size of all Pacific salmon, they’re probably the most sensitive to acidification.
A team led by University of British Columbia’s Michelle Ou and Colin Brauner reared pink salmon embryos from the Quinsam River Hatchery at current and projected CO2 levels, ranging from today’s 450 μatm to 2,000 μatm. After 10 weeks, they were transferred to saltwater tanks.
Measuring the oxygen consumption of developing pink salmon (with their yolks still attached). Michelle Ou
Hatchlings and juvenile pink salmon exposed to elevated CO2 levels showed reduced growth (in length and weight) during their freshwater development and even after they entered seawater. Their oxygen consumption, or metabolism, was also altered in a way that might harm their ability to find food, evade predators, and migrate through streams.
Additionally, the activity of their olfactory cells were reduced. Being able to “smell the water” is critical for returning to their spawning grounds and for sensing danger. Furthermore, these salmon also spent a lot more time in water containing alarm cues (chemicals mimicking other fish) and near novel tank objects (like a small Lego figurine). Being raised in higher CO2 levels seemed to have reduce anxiety in pink salmon fry. Being both smaller and less afraid is a dangerous combination of traits that could make them more susceptible to predation.
“The increase in carbon dioxide in water is actually quite small from a chemistry perspective so we didn’t expect to see so many effects,” Ou explains in a statement. “The growth, physiology and behavior of these developing pink salmon are very much influenced by these small changes.”