The Pacific Ocean has become so acidic that it is dissolving the shells of young Dungeness crabs on the northwest coast of the United States, where crabs are critical to the fishing economy.
This is according to a new study funded by NOAA, the US National Oceanic and Atmospheric Administration, in partnership with other researchers from the US, Canada, Slovenia and the UK. The work was published by the journal Science of the Total Environment.
"This is the first study to show that larval crabs are already affected by ocean acidification in the natural environment, and builds on previous understanding of the impacts of ocean acidification on pteropods." said lead author Nina Bednarsek, lead scientist for the Southern California Coastal Water Research Project.
"If crabs are already affected, we really need to make sure we start paying much more attention to the various components of the food chain before it is too late."
Scientists knew that ocean acidification was harming pteropods, which are small swimming snails that salmon, mackerel and herring feed on. However, they figured they wouldn't see similar damage to Dungeness crab, at least now, although their models suggested that could happen in a future climate change. However, the estimated increase in such damage is already 8.3 percent compared to 20 years ago.
"We found dissolution impacts on crab larvae that weren't expected to occur until much later in this century," said Richard Feely, principal scientist at NOAA's Pacific Marine Environmental Laboratory and one of the study's co-authors.
In fact, the future seems to have arrived. Ocean acidification occurs when the pH of ocean water is lowered, mainly due to the absorption of carbon dioxide from the atmosphere over long periods of time. That process means there are fewer carbonate ions in seawater, and those carbonates are essential building blocks for marine life, including coral.
"The decrease in carbonate ions can make it difficult for calcifying organisms to build and maintain shells and other calcium carbonate structures," explains NOAA. That spells trouble for oysters, clams, sea urchins, and crabs.
Analysis of young Dungeness crab samples collected during a 2016 marine research mission confirmed damage to the top layer, called the carapace, as well as the loss of small hair-like elements.
Crabs use these mechanoreceptors as a kind of navigational tool to orient themselves in their environments, essentially going bald when bristles fall off a shell that is no longer strong enough to support them.
Other changes to the shells included abnormal scars and ridges, which can affect the crabs' survival in terms of swimming, staying buoyant and upright, and escaping predators. The damaged crabs were smaller as well, suggesting they experience potential developmental delays.
Taken together, the findings appear to support a response consistent with the behaviors that scientists have seen when observing crustaceans deal with acidic conditions in laboratory settings. Bednarsek said he would like to see more research to better understand how damage to young crabs affects them later in life, in terms of their survival and ability to reproduce.