Award: OCE-1357665

Project objective: To investigate impacts of ocean acidification and warming on the calcification rate, elemental composition, mineralogy, and ultrastructure of a broad range of calcifying marine organisms. Funding from this award supported a wide range of experimental and field-based research projects investigating numerous aspects of the impacts of ocean acidification (OA) and global warming (GW) on marine calcification. Examples are summarized below. (1) Impact of OA on shell mineralogy of 18 species of marine calcifiers. OA alters mineral ratios of bi-mineralic calcifiers, but does not cause mono-mineralic calcifiers to start producing a new mineral, while also altering Mg/Ca ratios in some calcite-producing organisms. (2) Impact of OA on the chemistry of the calcifying fluids of corals and coccolithophores. Microelectrode and boron isotope measurements of coral skeletons show that although pH of coral calcifying fluid is substantially elevated relative to surrounding seawater, OA causes pH of this fluid to decline. However, corals target a fixed external:internal proton ratio, regardless of seawater pH. Boron isotope measurements of coccolith calcite show that coccolithophores maintain constant pH at site of calcification, allowing them to continue shell-building under OA. (3) Modelling calcification responses exhibited by organisms to OA. A simple and unified geochemical model of the calcifying fluids of marine calcifiers was developed that generates the full range of calcification responses that have been observed to date in various OA experiments (negative, neutral, positive). (4) Impact of GW on Caribbean reef-building corals. 100-year cores obtained from corals on the Meso-American Barrier Reef System (coastal Belize) indicate that warming has caused forereef corals (Siderastrea siderea) to decline, but not backreef or nearshore corals—suggesting that forereef corals are more vulnerable to GW. (5) Reconstructing past seawater pH. A boron isotope indicator of past seawater pH was developed for the coral Siderastrea siderea. (6) Impact of OA on calcification rates. Laboratory experiments show that OA has a negative effect on the calcification rates of juvenile American oysters, a neutral effect on the mud crab, and a parabolic (or æpeakedÆ) effect on the reef-building coral Siderastrea siderea. (7) Combined impacts of OA and GW. Laboratory experiments show that OA impairs calcification rates with the urchin Echinometra viridis, while GW has a positive effect. Thus, GW mitigates effect of OA on this species. Laboratory experiments also show that the coral Siderastrea siderea exhibits parabolic (peaked) calcification responses to both OA and GW, and that GW amplifies the negative effect of OA, and vice versa. (8) Impact of ocean acidification on behavior and predator-prey dynamics. Laboratory experiments show that OA renders mud crabs less effective at opening and consuming juvenile oysters. (9) Impact of OA and GW on stable isotopic composition of marine calcifiers. Laboratory experiments show that oxygen isotopes of urchin calcite and coral aragonite are negatively correlated with temperature and uncorrelated with pCO2, while carbon isotopes of the urchins were significantly correlated with both temperature and pCO2--suggesting that fossil urchin oxygen and carbon isotopes archive past oceanic temperature and pCO2, and that coral aragonite archives past temperature. (10) Impact of OA and GW on the clumped isotopes of bivalve shells. Laboratory experiments reveal a relationship between temperature, but not seawater saturation state, and the clumped isotope composition of bivalves—suggesting that clumped isotopes in bivalves archive past-ocean-temperature. (11) Impact of GW and OA on elemental composition of marine calcifiers. Laboratory experiments show that OA impacts elemental ratios within various marine calcifiers and that GW alters elemental r...