Meeting Abstract

37.6  Friday, Jan. 4  Rising CO₂ disproportionately affects extension versus mass deposition in reef corals MUEHLLEHNER, Nancy*; EDMUNDS, Peter J.; California State University, Northridge; California State University, Northridge nancymuehllehner@gmail.com

The production of mineral skeletons by reef corals has long interested biologists, but recent attention has focused on the role of increasing levels of atmospheric CO₂ in depressing rates of coral calcification. As atmospheric pCO₂ rises, seawater pH decreases, aragonite saturation state declines, and it becomes energetically more challenging for biogenic aragonite deposition. Although these conditions are known to decrease calcification in reef corals, such effects have been measured almost exclusively in terms of the mass deposition of aragonite. Interestingly, it remains virtually unknown how this translates into morphological consequences in a taxon well known for morphological plasticity. This study used manipulative experiments lasting 14 days to test the hypothesis that increasing pCO₂ has unequal relative effects on coral calcification and corallum structure. First, increased levels of CO₂ (700 vs 350 �atm) were tested for effects on the mass deposition (mg cm^-2 day^-1) and linear extension (μatm day^-1) of Acropora hyacinthus and Acropora pulchra from the lagoon of Moorea (French Polynesia), and second, the results were used to test for a trade-off between each measure of growth. Overall, mass deposition and linear extension were significantly reduced by high pCO₂ in both species, and for A. hyacinthus, several branches shrank through dissolution of the apical corallite. Importantly, linear extension was reduced nearly twice as much (47%) as mass deposition (26%) under elevated pCO₂, thereby demonstrating that morphological plasticity can play an important role in determining the response of corals to global climate change effects.