Ocean acidification threatens Dungeness crabs: Study
Ocean acidification is affecting the shells and sensory organs of young Dungeness crabs in West Coast waters, posing a threat to B.C.’S second most valuable seafood export.
A study published in the journal Science of the Total Environment found damage to upper shells and the hair-like sensory structures that larval crabs use to swim and avoid predators.
“We found dissolution impacts to the crab larvae that were not expected to occur until much later in this century,” said co-author Richard Feely, a senior scientist with the U.S. National Oceanic and Atmospheric Administration.
Surface waters of the ocean are becoming more acidic as they absorb more and more carbon dioxide, which is steadily increasing in the atmosphere due to human activities.
“If the crabs are affected already, we really need to make sure we start to pay much more attention to various components of the food chain before it is too late,” said lead author Nina Bednarsek, senior scientist with the Southern California Coastal Water Research Project.
B.C. exported about $159 million worth of crab last year, according to the Ministry of Agriculture sector snapshot. About 99 per cent of commercially harvested B.C. crab is Dungeness.
Scientists on both sides of the border have been testing the resilience of Dungeness crabs at various acidity levels in the laboratory, but NOAA scientists have now detected significant damage to crabs in the marine environment.
“This is the first study that demonstrates that larval crabs are already affected by ocean acidification in the natural environment, and builds on previous understanding of ocean acidification impacts on pteropods,” said Bednarsek.
Increased CO2 in seawater affects the availability of carbonate ions, used to build and maintain shells by crabs, oysters, clams, urchins, corals and other species.
Scientists have observed damage due to corrosive water in species other than crab in recent years, but the Dungeness finding is unusual, said Chris Harley, a professor of zoology at UBC.
“The surprise for me was that it was Dungeness crabs, because they were assumed to be quite resistant,” said Harley, who did not participate in the study. “This is certainly something that oyster growers are already concerned about.”
Crabs shed and regrow their shells regularly as they get bigger, while oysters and urchins that sustain damage carry that with them for life.
“We have seen this in the lab in oysters, mussels and abalone, and we know that the larval stage is really sensitive,” he said.
“This study is a nice reminder that these results from the field are real and something we should be concerned about.”
In the study, larval Dungeness crabs examined by electron microscope showed damage to the external shell and legs, which could affect their ability to navigate and to avoid predators. Damaged larvae were also smaller.
“What we don’t know is whether and when it will cause the Dungeness crab populations to decline,” said Harley. “This might be one of those early signals that it could decrease in the future.”