Date of Award

Summer 2021

Document Type


Degree Name

Doctor of Philosophy (PhD)


Ocean & Earth Sciences



Committee Director

Richard C. Zimmerman

Committee Member

Victoria J. Hill

Committee Member

Dreux P. Chapell

Committee Member

Dan Barshis


As CO2 levels in Earth’s atmosphere and oceans steadily rise, varying organismal responses may produce ecological losers and winners. Increased ocean CO2 can enhance seagrass productivity and thermal tolerance, providing some compensation for climate warming. However, the consistency of this CO2 effect across populations of cosmopolitan species such as Zostera marina L. (eelgrass) remains largely unknown. This study analyzed whole-plant performance metabolic profiles and gene expression patterns of distinct eelgrass populations in response to CO2 enrichment. Populations were transplanted from Nisqually Landing and Dumas Bay, two cold water environments in Puget Sound, WA (USA) that rarely experience summer water temperatures above 15° C, and one population from South Bay, VA (USA) that frequently experiences summer heat waves exceeding 25° C. All three populations were grown in outdoor aquaria and exposed to five different CO2 concentrations, under natural light and ambient water temperature of southeast Virginia, for 18 months. The three eelgrass populations showed similar instantaneous metabolic responses to CO2 treatments. However, only eelgrass from South Bay, VA and Dumas Bay, WA exhibited physiological stimulation to seasonally increasing temperature under elevated CO2 treatments, increasing shoot numbers, plant size, and leaf growth. The plants from Nisqually Landing, WA were unable to survive the warm summer water temperature even in the presence of high CO2 concentrations. Metabolomic profiling revealed differences among CO2 treatments and eelgrass populations. CO2 enrichment increased the abundance of Calvin Cycle and nitrogen assimilation metabolites while suppressing the abundance of stress-related metabolites. However, target genes involved in carbohydrate fixation, photosynthesis and proteins that function as molecular chaperones did not respond to CO2 enrichment even though they changed through in response to light and temperature. Transcriptome profiles by themselves did not predict how gene expression translates into physiological and metabolic consequences under high CO2 conditions. The differential response among eelgrass populations suggest that seagrass populations will respond variably to increasing CO2 concentrations in which some eelgrass phenotypes may be better suited to cope with an increasingly hot and sour sea than others.


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