Date of Award


Document Type

Honors Thesis



First Advisor

Thomas Arnold




Atmospheric carbon dioxide (CO2) has increased by about 40% since the Industrial Revolution, with current levels residing around 395ppm. A portion of this excess CO2 is absorbed by the oceans resulting in the increase of H+ and carbonic acid concentrations, as well as a corresponding reduction in mean pH. This phenomenon is termed ‘ocean acidification’ (OA). Multiple studies demonstrate a decline in calcification of many marine organisms as a result of OA, but greater photosynthetic productivity in algae and seagrasses has also been reported. However, little is known regarding the effects of OA on the chemical defenses produced by these marine angiosperms. Three forms of CO2 enrichment were utilized in this study to observe the effects OA may have on secondary metabolite accumulation in four species of seagrass. These include a Free Ocean Carbon Enrichment (F.O.C.E.) system – Severn River, MD (USA), a natural volcanic vent – Vulcano (Italy), and the naturally acidified Myora Springs – North Stradbroke Island (AUS). Additionally, herbivory tests examined preferences of juvenile black rabbitfish on eelgrass grown in low and normal pH regions near the naturally acidified Myora Spring (AUS). Phenolic acids, the main chemical defenses of these species, were identified and measured via HPLC, whereas more complex tannin concentrations were measured by colorimetry. The results of this experiment observed a significant decrease, about 60% in some instances, in the production of these secondary metabolites corresponding to a decrease in average oceanic pH and an increase in pCO2 concentrations. The reduction in the accumulation of these chemical defenses within the observed seagrasses implies a greater susceptibility to herbivory and harmful pathogens, which reveals location dependent impacts of OA on marine plants.