Scientists have new information about how pteropods, tiny marine creatures so important to food webs they’re known as the “potato chips of the sea,” may fare under compounding environmental stressors.“We found that changing ocean conditions affect pteropods in multiple, overlapping ways, some of which could also be detrimental for long-term pteropod population sustainability ” Nina Bednaršek, a biological oceanographer at Oregon State University’s Hatfield Marine Science Center and the paper’s lead author, says.
This research provides new insight into how pteropods in coastal waters are likely to respond to changing ocean conditions and can provide numerous insights to resource managers and policy makers to understand potential impacts of changing conditions on ocean life.
Tiny creatures, big impact
Pteropods are shelled snails and slugs no bigger than your fingernail. They are critical to coastal and oceanic food webs: many fish depend on pteropods for food, especially when other food is not available in the late summer and fall. Pteropods are highly sensitive to environmental stressors—for instance, prior studies have shown that pteropods are sensitive to ocean acidification, which makes it more difficult for pteropods to build their shells. The effects can become more severe when the stress from other factors, for example ocean warming and declining food availability, are added. The combined effects of these stressors are reflected in the thickness of individual pteropod shells and can be measured using imaging methods similar to the CT (or CAT) scans used in hospitals.
Understanding how pteropods will respond to multiple changing ocean conditions can give us insight into future changes to ocean ecosystems.
Sampling in the Salish Sea
Bednaršek and co-authors from the Washington Department of Ecology, the Japan Agency for Marine-Earth Science and Technology, and the University of Washington conducted their research in the southern Salish Sea, a large estuary with highly variable conditions. With support from the Washington Ocean Acidification Center, the scientists collected more than 900 pteropod samples from eight stations across the southern Salish Sea and one additional station on Washington’s outer coast. In the laboratory, they measured shell characteristics using CT scans to calculate shell length, density and thickness. They then used the computer model LiveOcean to look for associations between ocean conditions and shell characteristics.
The researchers found that pteropod shells are thinner and less dense under the stress of ocean acidification. Greater variation in temperature, including temperature extremes, led to additional negative effects on shell condition. However, in locations where more food was available, pteropods appeared to partially compensate by building thicker shells despite other unfavorable conditions. These findings suggest that habitats with lots of available food may, to a certain extent, help pteropods build shells under conditions of ocean acidification and warming.
The bottom line
Changing ocean conditions, including warming, marine heatwaves, and ocean acidification, may have compounding negative effects on the ability of pteropods to build and maintain their shells. If such changes are severe enough, or last long enough, pteropod populations could decline, and these declines could ultimately reduce the amount of food available to fish and other predators. Understanding the effects of multiple stressors on pteropods and other plankton species can help resource managers respond to changing ocean conditions for the benefit of the environment and the people who depend on these resources.
