RESUMO
Coral reefs, the largest bioconstruction on Earth, are formed by calcium carbonate skeletons of corals. Coral skeleton formation commonly referred to as calcification occurs in a specific compartment, the extracellular calcifying medium (ECM), located between the aboral ectoderm and the skeleton. Calcification models often assume a direct link between the surrounding seawater and the ECM. However, the ECM is separated from the seawater by several tissue layers and the cÅlenteron, which contains the cÅlenteric fluid found in both polyps and cÅnosarc (tissue connecting the polyps). Symbiotic dinoflagellate-containing cells line the cÅlenteron and their photosynthetic activity contributes to changes in the chemistry of the cÅlenteric fluid, particularly with respect to pH. The aim of our study is to compare cÅlenteron pH between the cÅnosarc and polyps and to compare areas of high or low dinoflagellate density based on tissue coloration. To achieve this, we use liquid ion exchange (LIX) pH microsensors to profile pH in the cÅlenteron of polyps and the cÅnosarc in different regions of the coral colony in light and darkness. We interpret our results in terms of what light and dark exposure means for proton gradients between the ECM and the coelenteron, and how this could affect calcification.
Assuntos
Antozoários , Calcinose , Animais , Concentração de Íons de Hidrogênio , Carbonato de Cálcio , Recifes de Corais , Água do MarRESUMO
Reef-building corals form their calcium carbonate skeletons within an extracellular calcifying medium (ECM). Despite the critical role of the ECM in coral calcification, ECM carbonate chemistry is poorly constrained in vivo, and full ECM carbonate chemistry has never been characterized based solely on direct in vivo measurements. Here, we measure pHECM in the growing edge of Stylophora pistillata by simultaneously using microsensors and the fluorescent dye SNARF-1, showing that, when measured at the same time and place, the results agree. We then conduct microscope-guided microsensor measurements of pH, [Ca2+], and [CO3 2-] in the ECM and, from this, determine [DIC]ECM and aragonite saturation state (Ωarag), showing that all parameters are elevated with respect to the surrounding seawater. Our study provides the most complete in vivo characterization of ECM carbonate chemistry parameters in a coral species to date, pointing to the key role of calcium- and carbon-concentrating mechanisms in coral calcification.