Meeting Abstract

P2.128  Sunday, Jan. 5 15:30  Increased Temperature and Lowered pH Alter Shell Mineralogy of the Scaled Giant Clam (Tridacna squamosa) ARMSTRONG, E.J.*; WATSON, S-.A.; CALOSI, P.; MUNDAY, P.; STILLMAN, J.; University of California, Berkeley; James Cook University; University of Plymouth; James Cook University; University of California, Berkeley and San Francisco State Univeristy armstrong@berkeley.edu

Elevated temperature and decreased oceanic pH are products of increased atmospheric pCO₂, and have been shown to alter mineral structure of carbonate exoskeletons in many marine taxa. The potentially synergistic effects of these stressors are likely to be particularly severe for tropical molluscs like giant clams that may currently live at or near their respective thermal maxima, and that produce the largest exoskeleton of all extant bivalves. We investigated the effects of increased temperature and pCO₂ on mineral composition and organic content of shells of the scaled giant clam (Tridacna squamosa). Juvenile clams were reared under one of four treatment conditions in a 2×2 temperature (28.5°C and 31.5°C) crossed with CO₂ (395 ppm and 950 ppm) experimental design. Clams were exposed to experimental conditions for 60 days before samples of both new and old growth shell were collected. Shell mineralogy (Ca²⁺, Mg²⁺, K⁺, Mn²⁺, Sr²⁺, P^3-, Si⁴⁺) and organic content (%C, %H, and %N) were examined using ICP-MS and elemental analysis respectively, and compared across all treatments. Under elevated temperature, Ca²⁺:Mg²⁺ in new shell decreased by 21.6% and 24.4% when compared to old growth under high and low pCO₂ respectively. %C and %H did not differ significantly between any of the treatments, but %N of new shell decreased by 62.8% under high pCO₂ and temperature. These results suggest alterations in both the organic and inorganic matrices of new shell formed under elevated temperature and pCO₂ and are consistent with an increased proportion of polysaccharides and amorphous CaCO3 present relative to proteins and aragonite respectively.