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article imageDungeness crabs' shells being eaten away by acidic Pacific Ocean

By Karen Graham     Jan 29, 2020 in Environment
As the Pacific Ocean becomes more acidic, Dungeness crabs, which live in coastal areas, are seeing their shells eaten away, according to a new study commissioned by the National Oceanic and Atmospheric Administration.
The study, released this week in the journal Science of the Total Environment is based on a NOAA West Coast Ocean Acidification (WCOA) cruise in May–June 2016 that included a survey of Oregon, Washington and British Columbia coastal waters that examined larval Dungeness.
The Dungeness crab - Metacarcinus magister - is vital to recreational and commercial fisheries in the Pacific Northwest. Ocean acidification was not expected to affect the crabs so quickly, according to experts, and researchers say this study is a warning for the future of seafood and the health of marine life.
“If the crabs are affected already, we need to make sure we start to pay attention to various components of the food chain before it is too late,” said Nina Bednarsek, the lead author among 13 contributing scientists, reports the Seattle Times.
Coastal habitats with the steepest ocean acidification gradients are most detrimental for larval Dun...
Coastal habitats with the steepest ocean acidification gradients are most detrimental for larval Dungeness crabs.
Nina Bednarsek et al
The commercial Dungeness crab industry is worth about $200 million annually, however, it is also a mainstay for recreational and tribal crabbers. In recent years, coastal waters have been found to contain "hot spots" of ocean acidification. This is the result of occasional upwellings of deeper ocean water rich in carbon dioxide and surface waters that also have absorbed the gas released by fossil-fuel combustion and other human activity.
“This makes our region very unique,” said Richard Feely, a senior scientist at NOAA’s Pacific Marine Environmental Laboratory, who was one of the co-authors of the new study.
The opening of the dungeness crab season was delayed in California in 2015. Above: A very large dung...
The opening of the dungeness crab season was delayed in California in 2015. Above: A very large dungeness crab.
Matt Withans
What the study found
The study itself integrated physical, geochemical, biological, and modeling components in the assessment of the Dungeness population. NOAA explains that when CO2 is absorbed by seawater, a chain of chemical reactions is set in motion. That causes the seawater to increase its acidity as an increase in hydrogen ions tamps down carbonate ions, which would keep the water's pH in balance.
Why is this important to know? Crustaceans and corals need carbonate ions to help them build strong shells. In the absence of enough carbonates, it becomes difficult for crabs, oysters, and clams to build shells. It also stops corals from building strong skeletons, per CNN News.
WET: Dungeness crabs are prepared for sale on the sidewalk outside the Fishermen s Grotto restaurant...
WET: Dungeness crabs are prepared for sale on the sidewalk outside the Fishermen's Grotto restaurant at Fisherman's Wharf in San Francisco.
Fred Hsu / Wikimedia Commons
Bottom line? The acidity of the ocean waters corrodes the shells of young Dungeness crab larvae, and likely impairs their ability to deter predators and regulate their buoyancy in the water, the researchers said. Additionally, the researchers saw something they had never seen before - The tiny hair-like structures crabs use to navigate their environments were damaged by the low pH levels,
"We found dissolution impacts to the crab larvae that were not expected to occur until much later in this century," said Feely.
The study concludes that there is clear evidence that marine invertebrates are damaged by extended exposure to strong present-day ocean acidity-related vertical gradients in their natural environment.
More about cungeress crabs, Pacific ocean, increased acidity, rising co2 levels, West coast
 
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