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Pteropod Shell Condition, Locomotion, and Long-term Population Trends in the Context of Ocean Acidification and Environmental Change

Alexander Bergan, Ph.D., 2017
Gareth Lawson, Advisor

Thecosome pteropods are zooplankton with aragonite shells that may experience dissolution and other adverse effects due to ocean acidification. I analyzed shell condition after exposing pteropods to elevated CO2 and in natural populations to investigate the sensitivity of the shells of different species to aragonite saturation state (ΩA). Limacina retroversa from laboratory experiments showed the clearest pattern of shell dissolution in response to decreased ΩA, while wild populations of Clio pyramidata and Limacina helicina either had non-significant regional trends or variability in shell condition that did not match with regional variability in ΩA. The sinking rates of L. retroversa from elevated CO2 treatments were slower in conjunction with worsened shell condition. These changes could increase their vulnerability to predators in the wild. Swimming ability was mostly unchanged by elevated CO2. I examined a long-term dataset of pteropods in the Gulf of Maine and did not observe a population decline between 1977 and 2015. Analysis of the habitat use of L. retroversa revealed seasonal associations with temperature, salinity, and bottom depths. The combination of laboratory experiments and field surveys helped to address gaps in knowledge about pteropod ecology and improve our understanding of the effects of ocean acidification on pteropods.