Tide pools at the front line of ocean acidification

By Becky Oskin

Beloved by beach goers, tide pools are also important ecological zones that provide shelter and food for many plants and animals.

Marine life living in tide pools are vulnerable to rising acid levels in seawater, according to new research from UC Davis, the Carnegie Institution for Science and UC Santa Cruz published March 18 in the journal Scientific Reports.

“The animals living in tide pools are already in a very stressful environment,” said study co-author Tessa Hill, an associate professor in the Department of Earth and Planetary Sciences and at the UC Davis Bodega Marine Laboratory, and associate director of the UC Davis Coastal and Marine Sciences Institute. “In the future, as ocean conditions change, tide pool organisms will spend more time in pools that are acidic enough to dissolve shells,” Hill said.

Study co-authors Lester Kwiatkowski and Yana Nebuchina taking samples from a rocky tide pool on the UC Bodega Marine Reserve. Photo credit: Ken Caldeira

Study co-authors Lester Kwiatkowski and Yana Nebuchina taking samples from a rocky tide pool on the UC Bodega Marine Reserve. Photo credit: Ken Caldeira

The world’s oceans are growing more acidic because of the sharp rise in atmospheric carbon dioxide during the past 200 years, a result of emissions from human activity. Increasing ocean acidity makes life difficult for organisms such as mussels, oysters and coralline algae, which build their shells and exoskeletons out of calcium carbonate. However, some marine life seems to thrive in more acidic waters, including tide pool predators such as sea stars and crabs.

How Tide Pools May Adapt to Ocean Acidification

In the study, the researchers document the effects of natural pH swings on marine life in rocky tide pools near the UC Davis Bodega Marine Laboratory. The team found carbon dioxide used during daytime photosynthesis helps balance ocean acidity, creating a favorable water environment for shell-builders. But at night, when plants and animals respire (and there is no photosynthesis), releasing carbon dioxide, the water’s pH level quickly becomes acidic.

During low tide at night, when the tide pools are cut off from the ocean, shells and skeletons may even start to dissolve, the study reports. The findings suggest increasing ocean acidity will put tide pools at risk by exacerbating these natural pH variations.

“This indicates that the first response to ocean acidification may be at nighttime in these restricted, coastal environments,” Hill said.

The protected lands of the Bodega Marine Reserve, part of the UC Natural Reserve System, have been instrumental in ocean acidification research at UC Davis. The reserve provides isolation from outside impacts, such as people walking among the tide pools. The new study is the most extensive set of ocean acidification measurements ever made in tide pools, the researchers said.

Tide pool animals may be the first at risk from ocean acidification

Tide pool animals may be the first at risk from ocean acidification.

Climate Change Threat

Separate research suggests the average ocean pH is three times more acidic than pre-industrial levels. Predictions by the Intergovernmental Panel on Climate Change (IPCC) the pH will continue to drop (become more acidic) through 2100. The conditions seen in nighttime tide pools during the study could occur up and down the Pacific coast by 2100.

“Unless carbon dioxide emissions are rapidly curtailed, we expect ocean acidification to continue to lower the pH of seawater,” said lead study author Lester Kwiatkowski, a postdoctoral researcher at the Carnegie Institution for Science in Washington, D.C. “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. Nobody really knows how our coastal ecosystems will respond to these corrosive waters, but it certainly won’t be well.”

Other Carnegie authors include Yana Nebuchina, Marine Sesboü and Ken Caldeira. Co-authors from UC Davis include Brian Gaylord, Jessica Hosfelt, Aaron Ninokawa, Ann Russell and Emily Rivest. Other co-authors include UC Santa Cruz professor Kristy Kroeker.

More information

Read the paper

More photos from the study

UC Davis Bodega Marine Laboratory

Becky Oskin writes for the Division of Mathematical and Physical Sciences, College of Letters and Science. Follow her on Twitter @beckyoskin.

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