A newly published scientific study has found that ocean acidification caused by climate change is damaging shellfish such as mussels and oysters. The information for the study came from the most extensive set of measurements ever made in the tide pools along the California coast. The measurements were made by scientists from the Carnegie Institution for Science, the University of California at Davis, and the University of California at Santa Cruz.
The study, Nighttime dissolution in a temperate coastal ocean ecosystem increases under acidification, was published last week in Scientific Reports, an online scientific journal.
According to the study, carbon dioxide (CO2) emissions from humans burning fossil fuels are causing ocean acidification and that acidification is damaging shellfish, which are calcifying organisms.
The National Oceanic and Atmospheric Administration (NOAA) describes ocean acidification this way. “When CO2 is absorbed by seawater, a series of chemical reactions occur resulting in the increased concentration of hydrogen ions. This increase causes the seawater to become more acidic and causes carbonate ions to be relatively less abundant. Carbonate ions are an important building block of structures such as sea shells and coral skeletons. Decreases in carbonate ions can make building and maintaining shells and other calcium carbonate structures difficult for calcifying organisms such as oysters, clams, sea urchins, shallow water corals, deep sea corals, and calcareous plankton.”
The increased ocean acidity caused by global warming makes it difficult for organisms, such as mussels and oysters that construct their shells and exoskeletons out of calcium carbonate, to continue to build these protective layers. The scientists found that in high enough concentrations, carbon dioxide in seawater can even cause these shells and skeletons to dissolve entirely.
The tide pools along the California coast are isolated from the open ocean during low tides, and that creates the situation that is damaging to shell fish. Photosynthesis is the process by which plants use the sun’s energy to convert carbon dioxide and water into sugar, which they use as food. As the plants convert carbon dioxide and water into sugar, they give off oxygen in the process. During daylight hours, photosynthesis removes carbon dioxide from the seawater and this acts to reverse the effects of ocean acidification. At night, however, photosynthesis stops, and the respiration of plants and animals takes up oxygen and releases carbon dioxide into the sea water, which exacerbates the effects of ocean acidification, and increases the risk to calcifying organisms such as mussels and oysters.
The scientists conducted the study in California’s natural rocky tide pools near the University of California at Davis’s Bodega Marine Laboratory. They found that the rate of shell and skeletal growth was not greatly affected by seawater chemistry in the daytime. On the other hand, during low tide at night, water in the tide pools became corrosive to calcium carbonate shells and skeletons. The study found evidence that the rate at which these shells and skeletons dissolved during these nighttime periods was greatly affected by seawater chemistry.
Lead author Lester Kwiatkowski of the Carnegie Institution of Science summed up the results of the study this way. “Unless carbon dioxide emissions are rapidly curtailed, we expect ocean acidification to continue to lower the pH of seawater. This work highlights that even in today’s temperate coastal oceans, calcifying species, such as mussels and coralline algae, can dissolve during the night due to the more acidic conditions caused by community respiration.”