Meeting Abstract

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 craftjd@gmail.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.