Estimating relative sensitivities of zooplankton to ocean acidification and comparing to observations in situ

Abstract

Laboratory studies show that low pH and high pCO2 associated with ocean acidification can significantly affect the physiology and survival of zooplankton, with differential responses among taxa. To understand how sensitivity to ocean acidification varies among zooplankton taxa, I performed a meta-analysis of the published literature, focusing on eight taxonomic groups of zooplankton found in marine waters of the U.S. Pacific Northwest. According to the metaanalysis, pteropods are the taxon most sensitive to increasing levels of pCO2 and calcification is the process most severely affected, while larvaceans and metabolism are the least sensitive taxon and process, respectively, examined in this study. I hypothesized that the relative sensitivities to pCO2 reported in the literature would explain a significant amount of variation in zooplankton ii abundance in Puget Sound, WA (USA), where pCO2 is known to vary across short spatial and temporal scales. To test this hypothesis, I collected zooplankton samples and environmental data on two research cruises in June and August 2017. Copepods, a highly sensitive taxon according to the meta-analysis, were consistently the most abundant taxon, while larvaceans, the least sensitive taxon, reached high abundance in a few samples. Statistical analyses revealed that a combination of temperature, fluorescence, dissolved oxygen, and salinity was the primary determinant of zooplankton abundance at these stations during the two sampling periods. I found little association between empirical measures of station pH and the abundance of sensitive taxa as revealed by the meta-analysis, calling into question the coherence between laboratory and field studies and suggesting that sensitivity to existing levels of ocean acidification may play a subordinate role in determining the abundance of some zooplankton taxa in this inland sea. The results of this study have important ramifications for long-term monitoring programs, especially with regard to the utility of measures of abundance as an indicator of response to environmental change.