The survival of marine organisms such as mussels and oysters living in small tide pools along California's rocky coastline may be threatened as ocean acidification exacerbates normal changes in ocean chemistry that occur overnight.
Mussels and oysters, for example, have calcium carbonate shells. However, increasing ocean acidity makes it difficult for organisms to build their outer protective layers. In fact, in high enough concentrations, carbon dioxide can even cause the calcium carbonate shells and exoskeletons of marine organisms to dissolve entirely.
Based on the most extensive set of measurements taken of tidal pools to date, researchers from the Carnegie Institution for Science found that the rate at which these shells and skeletons dissolved at night, when tides are low, was greatly affected by seawater chemistry.
"Unless carbon dioxide emissions are rapidly curtailed, we expect ocean acidification to continue to lower the pH of seawater," said Lester Kwiatkowski, lead author of the study. "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."
Atmospheric carbon dioxide is absorbed by the oceans, which, in turn, alters the seawater chemistry, making it more acidic - resulting in a lower pH. This process is called "ocean acidification."
For their study, researchers observed a variety of California's natural rocky tide pools surrounding the University of California, Davis Bodega Marine Laboratory. Tide pools are isolated from the open ocean during low tides. During the day, photosynthesis - the process by which plants convert the Sun's energy and atmospheric carbon dioxide into sugar, giving off oxygen - naturally removes carbon dioxide from the seawater in these small pools, in part reversing the effects of ocean acidification.
Therefore, during the day, researchers found that the rate of shell and skeletal growth is not greatly affected by seawater chemistry.
At night, however, plants and animals respire. This means that oxygen is taken from the pools and replaced with increasing amounts of carbon dioxide. Researchers found that this greatly exacerbates the effects of ocean acidification, making tide pools more corrosive to calcium carbonate and putting calcifying organisms at a great risk of shell deterioration.
"If what we see happening along California's coast today is indicative of what will continue in the coming decades, by the year 2050 there will likely be twice as much nighttime dissolution as there is today," added Ken Caldeira, study co-author. "Nobody really knows how our coastal ecosystems will respond to these corrosive waters, but it certainly won't be well."
Their findings were recently published in the journal Scientific Reports.
