Microzooplankton grazing, growth and gross growth efficiency are affected by pCO2 induced changes in phytoplankton biology

• Main Author: Still, Kelly
• Format: Text
• Language: English
• Published: Western CEDAR 2016
• Subjects: Environmental Sciences; Ocean acidification
• Online Access: https://cedar.wwu.edu/wwuet/478; https://doi.org/10.25710/kmdq-bj83; https://cedar.wwu.edu/context/wwuet/article/1490/viewcontent/Kelly_Still__Risenhoover__Edited_5.11.16.pdf

Accumulating evidence shows that ocean acidification (OA) alters surface ocean chemistry and, in turn, affects aspects of phytoplankton biology. However, very little research has been done to determine if OA-induced changes to phytoplankton morphology, physiology and biochemistry may indirectly affect microzooplankton, the primary consumers of phytoplankton. This is one of the first studies to explore how OA may indirectly affect microzooplankton ingestion, population growth and gross growth efficiency (GGE). I hypothesized 1) that the physiology, biochemistry and morphology of the phytoplankton Rhodomonas sp. would be directly affected by elevated pCO2 and 2) that pCO2-induced changes in Rhodomonas sp. would affect grazing, growth rates, and GGE in microzooplankton consumers. To test my first hypothesis, I cultured the ecologically important phytoplankton, Rhodomonas sp., semi-continuously for 17 days under three pCO2 treatments (400ppmv, 750ppmv and 1000ppmv). During this time I characterized Rhodomonas sp. cell size, C:N, cellular total lipids, growth rate, cellular chlorophyll a concentrations and carbohydrates. Rhodomonas sp. cell bio-volume and total cellular lipids were the only aspects of Rhodomonas sp. found to be significantly affected by pCO2. On average, Rhodomonas sp. cell bio-volume increased by ~60% and ~100% and total cellular lipids increased by 36% and 50% when cultured under moderate and high pCO2 treatments, respectively, compared to the ambient treatment. To test my second hypothesis, the pCO2-acclimated Rhodomonas sp. were fed to four microzooplankton species, two tintinnid ciliates (Favella ehrenbergii (recent name change to Schmidingerella sp.) and Coxliella sp.) and two heterotrophic dinoflagellates (Gyrodinium dominans and Oxyrrhis marina). Two experimental designs were used to test whether microzooplankton grazing and growth are affected by OA through changes in prey state. My data confirm my hypothesis that microzooplankton grazing is affected by OA-induced changes to their prey. In ...