Water breathability affects where anchovies can survive

Marine species thrive in ocean regions that meet their oxygen needs, according to a new study from the University of Washington. For anchovies, the research suggests that much of their range in the Pacific Ocean will become uninhabitable in the coming decades. 

The research was based on the understanding that marine species respond to the “breathability” of their surrounding water, which is influenced by a combination of the oxygen levels present, water temperature, and the oxygen needs of particular species. 

The experts combined their knowledge of water breathability with historical data to explain population cycles of anchovies that inhabit the California Current off the western coast of the United States.

“If you’re worried about marine life off the west coast of North America, you’re worried about anchovies and other forage fish in the California Current. Ultimately it’s what underpins the food web,” said study lead author Evan Howard.

“Climate change isn’t just warming the oceans – it is causing oxygen to decrease, which could force fish and other ocean animals to move away from their normal range to find higher-oxygen waters.”

Anchovy populations are known to fluctuate over time, but the reasons for this are unclear. Previous explanations, such as food availability or competition, failed to fully clarify the anchovy population cycles from the 1950s to present day.

Since the late 1940s, the California Cooperative Oceanic Fisheries Investigations (CalCOFI) has monitored marine life and conditions offshore. 

“They weren’t just measuring anchovies, they were measuring everything they could get their hands on,” said Howard.

In 2015, the UW team demonstrated that water breathability, or the combined effects of temperature and oxygen levels, are key for the survival of marine animals. 

For the current study, the researchers combined observations with ocean models to fill gaps in the data. The team showed that the breathability index changes over time, and that it has corresponded with the rise and fall of anchovy populations over the last several decades.

“This study is the first one that demonstrates on a timescale of decades that a species is responding in really close alignment with this metabolic index – how breathable the ocean in its habitat has become,” said study senior author Professor Curtis Deutsch. “It adds a new, independent line of verification that species in the ocean are arranged in accordance with how breathable their habitats are.”

According to the study, projected changes in ocean conditions could make the southern part of the anchovies’ range, which is off the coast of Mexico and Southern California, uninhabitable by 2100.

“We expect habitats to shift for all species that depend on oxygen for survival,” said Howard. “If we understand how these animals are responding to their environment, we can better predict how these populations will be affected as the conditions change.”

The study is published in the journal Science Advances.

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By Chrissy Sexton, Earth.com Staff