P1.30 Wednesday, Jan. 4 Impacts of ocean acidification on growth, calcification, and terpene concentrations in the green alga Halimeda opuntia CRAFT, Jonathan D*; RITSON-WILLIAMS, R; LANGDON, C; PAUL, V; Smithsonian Marine Station, Fort Pierce email@example.com
Increases in atmospheric carbon dioxide concentrations are reducing ocean pH and the calcification rates of marine organisms. Many calcified invertebrates and macroalgae need aragonite-saturated seawater to deposit calcium carbonate. Additionally, changes in carbon dioxide concentrations may cause sub-lethal stress to organisms and changes in concentrations of secondary metabolites (e.g., terpenes) that protect macroalgae from herbivores. We exposed a calcareous terpene-producing macroalga, Halimeda opuntia, to seawater conditioned with increasing levels of atmospheric carbon dioxide (CO2) to test for affects of ocean acidification on growth, calcification, and terpene concentrations. Growth and terpene concentrations did not differ among CO2 levels that spanned 300-4100 ppm. However, calcification decreased with increasing CO2 at levels over 1400ppm. Thus, growth and terpene concentrations in H. opuntia will not be impacted by the increases in atmospheric CO2 predicted to occur at the end of the century, but calcification in this alga will decrease when atmospheric CO2 levels exceed 2200 ppm. Halimeda opuntia is a conspicuous community member on coral reefs and in seagrass beds in tropical seas the world over, and the observed tolerance of this alga to increasing CO2 suggests that it will continue to be a prolific community member. However, the success of Halimeda opuntia in a high CO2 future could be to the detriment of more sensitive competitors such as corals.