Daily Earth Science Environment Repost

A crab crisis from coastal water acidification

My wife and daughters ate fresh cooked Dungeness crab yesterday evening for an appetizer. Fresh crab is a treat they occasionally enjoy during the West Coast Dungeness season. Ironically, that evening brought news from the National Oceanic and Atmospheric Administration (NOAA) that coastal water acidification threatens the Dungeness crab population. It seems that lower pH (higher acidity) in the ocean waters negatively impacts these crabs during their larval stage; bad news for crab lovers and for the fishermen whose livelihoods depend on the crab harvest.

Each year about 25% to 30% of the carbon dioxide (CO2) emitted into the atmosphere from burning fossil fuels ends up in the oceans. Upon absorption into the sea, CO2 reacts with ocean water to form carbonic acid, a reaction that increases the number of hydrogen ions in the water, thus decreasing the pH and raising the acidity. 

NOAA research documented the damage done by higher acidity (lower pH) waters in the U.S. Pacific Northwest coastal waters. Increased acidity damages the upper shells of larval Dungeness crabs, and also results in the loss of sensory structures they use to orient themselves to their surrounding environment.

This research was the first documentation of such shell damage and loss of hair-like sensors (mechanoreceptors) on the larval shells. These receptors detect chemical and mechanical stimuli, thus letting the crabs navigate through their environment. More research is needed to fully understand the long-term effects of larval damage. However, the study raises concerns about a potential Dungeness crab population decline in important West Coast fisheries.

Foraminifera define the change

NOAA research in 2019 showed that coastal waters off California had abnormally low pH (high acidity). The waters in these economically valuable coastal fisheries are acidifying twice as fast as the global average. Studies documenting this rapid acidification used seafloor cores. Examination of the cores allowed measurements of changes in foraminifera shell thicknesses over the past century. 

Planktonic foraminifera are microscopic, single-cell creatures that build tiny shells by extracting calcium carbonate and other minerals from the ocean water. Interestingly, the foraminifera fossil record demonstrates their existence in our oceans for over 500 million years.

The oceans are a carbon sink, and the increased supply of atmospheric CO2 translates into increasing amounts of carbon in the world’s oceans. This process is unfortunate for foraminifera because extra CO2 means more bicarbonate, and not more of the carbonate ions that these organisms need for building shells. With higher acidity, foraminifera have less chemical building blocks to make their shells, and thus their shells are thinner. Therefore, scientists can determine historic acidity levels by measuring shell thicknesses over time.

High acidity in coastal waters

Coastal waters off of California have a natural acidity cycle derived from the Pacific Decadal Oscillation (PDO). The PDO is a cycle of warming and cooling in the Pacific Ocean. This cycle also drives the amount of deep-water upwelling occurring along the U.S. West Coast.  Upwelling is an important factor because it brings colder, more acidic water to the ocean’s surface.

Surface waters are already acidifying from the absorption of increasing amounts of CO2 related to human industrial and commercial activity. Hence, the mixing of these deep, acidic waters with surface waters is part of the puzzle on why coastal water acidification along the U.S. West Coast oceans occurs more rapidly than the global average. 

More research is needed to understand the marine dynamics that dominate these coastal waters. However, the stakes are high given the economic value of fisheries that depend on Pacific coastal ecosystems. These waters are hatcheries and nurseries for many species. Their importance in the early life cycle of so many animals compounds both the problem and the economic fallout.


Acid and phytoplankton in the ocean’s food chain (Source: ArcheanWeb) – https://archeanweb.com/2020/01/28/acid-and-phytoplankton-the-oceans-food-chain/ Also:

Ocean Acidification (Source: ArcheanWeb) – https://archeanweb.com/2019/12/24/ocean-acidification-caused-by-co2/ Also:


Ocean Acidification Case Study: Dungeness Crab (NOAA) – https://nmssanctuaries.blob.core.windows.net/sanctuaries-prod/media/archive/education/pdfs/dungeness_crab_oa_fact_sheet.pdf Also:

Dungeness crab larvae already showing effects of coastal acidification (NOAA) – https://research.noaa.gov/article/ArtMID/587/ArticleID/2581/Dungeness-crab-showing-impact-of-coastal-acidification Also:

Tiny shells reveal waters off California are acidifying twice as fast as the global ocean (NOAA) – https://research.noaa.gov/article/ArtMID/587/ArticleID/2573 Also:

Foraminifera (Smithsonian) – https://ocean.si.edu/ocean-life/plankton/foraminifera Also:

Waters Off California Acidifying Faster Than Rest of Oceans, Study Shows (By Kendra Pierre-Louis; New York Times) – https://www.nytimes.com/2019/12/16/climate/california-ocean-acidifying.html Also:

California’s Coastal Waters Are Acidifying Twice As Fast As The Global Average (By Kristy Hamilton; IFLScience) – https://www.iflscience.com/environment/californias-coastal-waters-are-acidifying-twice-as-fast-as-the-global-average/ Also:

Feature Image: 2000600p587EDNmainimg-Crabapalooza (NOAA) (Modified) – Public Domain from NOAA publication

William House
William is an earth scientist and writer with an interest in providing the science "backstory" for breaking environmental, earth science, and climate change news.