Project: EAPSI: Effects of Ocean Acidification and Eutrophication on the Green Macroalgae Ulva spp.

Extracted from the NSF award abstract:

This award supports research that will investigate how the changing marine environment affects the growth rate of a weedy macroalgae, Ulva spp. Two factors that may act synergistically on Ulva spp. growth rates are ocean acidification and eutrophication. Ocean acidification is caused by increasing absorption of atmospheric carbon dioxide in seawater, which changes water chemistry and lowers pH. Eutrophication is caused mainly by human activities increasing the nutrients in seawater. Eutrophication alone is known to cause green-tide blooms of Ulva spp., and it is predicted that ocean acidification may increase growth rates of Ulva spp. because of increased carbon dioxide availability. How these two factors affect the growth rate when occurring simultaneously has not been thoroughly investigated. A state of the art ocean acidification incubation system will be used to investigate the synergy of these effects at the University of Tasmania in collaboration with Dr. Catriona Hurd, an expert in macroalgal physiology. Ocean acidification is occurring worldwide and eutrophication occurs near heavily populated coasts. This project will increase our ability to make predictions about the abundance of Ulva spp. in future marine environments.

Ocean acidification changes seawater chemistry by increasing the CO2(aq) concentration, which is the form of carbon used by the photosynthetic substrate Rubisco. Presently, dissolved CO2 in water makes up less than 1% of the total inorganic carbon in seawater. The more abundant form of inorganic carbon is bicarbonate (H2CO3). Most macroalgae can utilize both forms of inorganic carbon for photosynthesis, however the uptake of CO2 is less energetically costly as it occurs via passive diffusion through the cell membrane. Uptake of H2CO3 requires energy for carbon uptake, so we predict that the increase in CO2 may result in energetic savings that can be allocated to growth and nutrient uptake. This project will investigate if increasing dissolved CO2 will increase the ability of Ulva spp. to perform nutrient uptake of nitrogen. The results of this experiment will inform us about how human activities and environmental factors interact in future climate conditions for marine primary producers. This NSF EAPSI award supports the research of a U.S. graduate student and is funded in collaboration with the Australian Academy of Science.