A new study commissioned by the National Oceanic and Atmospheric Administration (NOAA) and published recently on Science of the Total Environment journal has found that the rising acidity level of the Pacific Ocean is eating away at the carapaces and exoskeletons of Dungeness crabs, damaging their sensory organs. Even more worrisome, the pace of the damage, according to the study’s authors, is accelerating faster than what had originally been projected, foreshadowing an unpleasant future for Dungeness crabs if this trend continues.

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“If the crabs are affected already, we really need to make sure we pay much more attention to various components of the food chain before it is too late,” said research team lead Nina Bednarsek, a senior scientist with the Southern California Coastal Water Research Project.

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Increased atmospheric carbon dioxide levels set in motion increased carbon dioxide absorption by the water, thus lowering the ocean’s pH levels. NOAA has reported that the ocean absorbs about one-third of the carbon dioxide released into the atmosphere via fossil fuel misuse and land-associated carbon emissions (ranching, logging, forest fires, etc.). As carbon dioxide is absorbed by the ocean, the water becomes “more acidic and causes carbonate ions to be relatively less abundant.” These carbonate ions are necessary for Dungeness crabs and other marine organisms to create, build and maintain their exoskeletons. Besides crustaceans, other affected organisms include mollusks, echinoderms, corals and calcareous plankton.

For the Dungeness crabs, especially their larvae, decreased carbonate ions in the acidic seawater means they are unable to craft exoskeletons to deter predators or even to normally develop. Delayed development further hinders maturation rates and, by extension, the species’ overall population growth.

The researchers were also surprised to discover that with abnormal shells damaged by the low pH levels, many of the crabs were correspondingly without certain mechanoreceptors necessary for proper swimming and vital sensory and behavioral functions. Abnormal movements made them vulnerable to predatory attacks and similarly prevented them from properly searching for food. In aggregate, the crabs’ chances for survival into adulthood decreases.

NOAA’s work has always been to inform local fisheries and conservation endeavors. It is hoped the study’s results will convince policy makers to take immediate action against rampant greenhouse gas emissions to curtail atmospheric carbon dioxide levels and reduce ocean acidification.

+ Science of the Total Environment


Image via Jerry Kirkhart