“We found dissolution impacts to the crab larvae that were not expected to occur until much later in this century,” said Richard Feely, a senior NOAA marine scientist.
Acidic ocean is dissolving crab shells earlier than predicted
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 the crabs are critical to the fishing economy.
That’s according to a new study funded by NOAA, the U.S. National Oceanic and Atmospheric Administration, in partnership with other researchers from the U.S., Canada, Slovenia and the United Kingdom. Their work was just made available online by the journal Science of the Total 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 lead author Nina Bednarsek, senior scientist with the Southern California Coastal Water Research Project. “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.”
The scientists knew that ocean acidification was damaging the pteropods, which are tiny swimming snails on which salmon, mackerel and herring feed. Yet they thought they would not see similar damage in the Dungeness crab, at least now, although their models suggested that could happen in a climate-change future. Yet the estimated increase in such damage is already 8.3 percent when compared with 20 years ago.
“We found dissolution impacts to the crab larvae that were not expected to occur until much later in this century,” said Richard Feely, a senior scientist with NOAA’s Pacific Marine Environmental Laboratory and one of the co-authors of the study.
Indeed, the future appears to have arrived. Ocean acidification happens when the pH of ocean water is lowered, primarily because of absorbing carbon dioxide from the atmosphere over long time spans. That process means there are less carbonate ions in the seawater, and those carbonates are essential building blocks for some marine life, including coral.
“Decreases in carbonate ions can make building and maintaining shells and other calcium carbonate structures difficult for calcifying organisms,” explains NOAA. That spells trouble for oysters, clams, sea urchins and the crabs.
The analysis of the young Dungeness crab samples collected during a 2016 marine research mission confirmed the damage to the upper shell, called a carapace, as well as loss of tiny hair-like elements. The crabs use these mechanoreceptors as a kind of navigational tool in order to orient themselves in their environments, and they essentially “go bald” as the bristles fall out of a shell that’s no longer strong enough to hold them.
Other changes to the shells included scarring and abnormal ridging, which may impact the crabs’ survival in terms of swimming, staying buoyant and upright, and escaping from predators. The damaged crabs also were smaller, suggesting that they experience possible developmental delays.
Taken together, the findings appear to support an answer consistent with behaviors the scientists have seen when watching the crustaceans deal with acidic conditions in laboratory settings. Bednarsek said she’d like to see more research to better understand how the damage in young crabs affects them later in life, in terms of their survival and ability to reproduce.