Search

A general decline in coral calcification has been observed in response to ocean acidification. It has recently been shown that heterotrophic feeding (the acquisition of organic nutrients) enables one massive coral species to maintain its calcification rates while exposed to ocean acidification but the consequences of higher seawater partial pressure of CO2 (P-CO2) on coral feeding capacities themselves have never been investigated. Exposing long-term acclimated starved and fed colonies of the major reef builder Stylophora pistillata to either ambient pH(T) (8.06 +/- 0.05; 417 Pa P-CO2) or low pH(T) (7.51 +/- 0.06; 1697 Pa P-CO2) showed that higher feeding rates can counterbalance the negative effects of seawater acidification on coral calcification. Indeed, relative to unfed corals under ambient pH(T) conditions, calcification rates in unfed corals decreased by 53.6% but remained constant in fed corals under high P-CO2 conditions. Results also clearly show that acidification affects the feeding capacity and feeding effort of the branching coral S. pistillata. Organic nutrient acquisition was severely reduced under high P-CO2, with a simultaneous decrease in the dissolved free amino acid uptake rates, the alkaline phosphatase activities, and the feeding rates on Artemia salina nauplii. Considering that all these processes are needed to fulfill the nutrient needs of the symbiotic association, on a long-term basis, lower feeding rates will likely aggravate the already fragile physiological state of many corals under warmer, more acidic conditions.

This paper presents the results of an effort to label calcium carbonates formed by marine organisms with stable isotopes to obtain information about the biomineralization processes. The growing skeleton of the scleractinian coral Porites porites was labeled three times with enhanced abundances of Sr-86. The distribution of Sr-86 in the skeleton was imaged with the NanoSIMS ion microprobe with a spatial resolution of similar to 200 nm and combined with images of the skeletal ultra-structure. Importantly, the distribution of the Sr-86 label in the P. porites skeleton was found to be strongly heterogeneous. This constrains the physical dimensions of the hypothetical Extracellular Calcifying Fluid (ECF) reservoir at the surface of the growing skeleton, which is implicit in most geochemical models for coral biomineralization. These new experimental capabilities allow for a much more detailed view of the growth dynamics for a wide range of marine organisms that biomineralize carbonate structures. Citation: Houlbreque, F., A. Meibom, J.-P. Cuif, J. Stolarski, Y. Marrocchi, C. Ferrier-Pages, I. Domart-Coulon, and R. B. Dunbar ( 2009), Strontium-86 labeling experiments show spatially heterogeneous skeletal formation in the scleractinian coral Porites porites, Geophys. Res. Lett., 36, L04604, doi: 10.1029/2008GL036782.