Ocean acidification. (Image: NOAA)

Oceanic acidification could have a strong impact on Dungeness crab

UNITED STATES
Monday, January 16, 2017, 23:10 (GMT + 9)

Acidification of the ocean, which is the result of the increasing amount of carbon dioxide in the atmosphere absorbed by the sea, will impact the West Coast seafood network, but not necessarily in the expected way.

Dungeness crab fisheries valued at about USD 220 million annually may face a strong decrease over the next 50 years due to food sources decline, according to the research published in the journal Global Change Biology.

However, according to the study, 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.

“What stands out is that some groups you’d expect to do poorly don’t necessarily do so badly, that’s probably the most important takeaway here,” explained Kristin Marshall, lead author of the study who conducted the research as a postdoctoral research associate at the University of Washington and NOAA Fisheries’ Northwest Fisheries Science Centre.

While previous studies have examined the vulnerability of particular species to acidification in laboratories, this is among the first to model the effects across an entire ecosystem and estimate the impacts on commercial fisheries.

The research, funded by the NOAA Ocean Acidification Program and the National Centres for Coastal Ocean Science and by a National Research Council fellowship, used sophisticated models of the California Current ecosystem off the Pacific Coast 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.

The California Current is 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.

The research is based on an earlier study by NOAA scientists Shallin Busch and Paul McElhany that quantified the sensitivity of various species to acidification, as originally reported in 393 separate papers.

In a new approach, Busch and McElhany weighed the evidence for each species based on its reported sensitivity in the laboratory, relevance to the California Current, and agreement between studies and identified ten groups of species with highest vulnerability to acidification.

Marshall and colleagues incorporated this into the ecosystem model to examine how acidification will play out in nature.

The study particularly 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.

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.

Since Dungeness crab is one of the most valuable fisheries on the West Coast, its decline would have some of the most severe economic effects, according to the research.

Groundfish such as petrale sole, Dover sole and deep-dwelling rockfish are also expected to decline due to acidification, according to the assessment. However, fisheries for those species are much less valuable so the economic impact would not be as large.

Coastal pelagic fish were only slightly affected.

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