Ocean acidification expected to impact marine food web on U.S. West Coast: study

The ocean acidification is expected to reverberate through the marine food web on the U.S. West Coast, as seawater absorbs increasing amounts of carbon dioxide from the atmosphere, a new study shows.

The ocean absorbs about one-third of carbon dioxide released into the atmosphere from the burning of fossil fuels, which has led to a 0.1 unit drop in pH, short for potential of hydrogen, a numeric scale of acidity or basicity from 0 to 14, with 7 being neutral, since the mid-1700s.

While previous studies have examined the vulnerability of particular species to acidification in laboratories, the new study published in the latest issue of the journal Global Change Biology is among the first to model the effects across an entire ecosystem and estimate the impacts on commercial fisheries.

Researchers used models of the California Current ecosystem, considered especially vulnerable to acidification because the upwelling of deep, nutrient-rich water low in pH already influences the West Coast through certain parts of the year, to assess the impacts of a projected 0.2 unit decline in the pH of seawater in the next 50 years, which equates to a 55 percent increase in acidity.

Built on an earlier effort by U.S. National Oceanic and Atmospheric Administration (NOAA) scientists Shallin Busch and Paul McElhany that quantified the sensitivity of various species to acidification and identified 10 groups of species with highest vulnerability, the study examined the effects on commercially important species including Dungeness crab; groundfish such as rockfish, sole and hake; and coastal pelagic fish such as sardines and anchovy over the period from 2013 to 2063.

"This was basically a vulnerability assessment to sharpen our view of where the effects are likely to be the greatest and what we should be most concerned about in terms of how the system will respond," said Tim Essington, a University of Washington (UW) professor of aquatic and fishery sciences and a co-author of the research.

Among their findings, Dungeness crabs, currently valued at about 220 million U.S. dollars annually and as one of the most valuable fisheries on the West Coast, will likely suffer over the next 50 years. Although earlier studies have shown that Dungeness crab larvae is vulnerable to acidification, the assessment found that the species declined largely in response to declines in its prey, including bivalves such as clams and other bottom-dwelling invertebrate species.

Groundfish such as petrale sole, Dover sole and deep-dwelling rockfish are also expected to decline due to acidification, according to the assessment. Pteropods and copepods, tiny marine organisms with shells that are vulnerable to acidification, will likely experience only a slight overall decline because they are prolific enough to offset much of the impact.

Meanwhile, marine mammals and seabirds are less likely to be affected by ocean acidification.

"What stands out is that some groups you'd expect to do poorly don't necessarily do so badly," Kristin Marshall, lead author of the study who pursued the research as a postdoctoral researcher at UW and NOAA Fisheries' Northwest Fisheries Science Center, was quoted as saying in a news release from UW. "This is a testament in part to the system's resilience to these projected impacts." Endit