Biophysical analysis of bioenergetics on coral slices

Coral algal symbiont (Symbiodiniaceae) has been subjected to different kind of studies to understand the role of photosynthesis and its regulatory mechanisms in the healthiness of coral reefs. Many biophysical studies have been conducted on free living algae, but few less on symbiotic corals due to technical constraints to have optically optimal biological samples. In this study we describe the use of small fragments of corals to study bioenergetic processes. Coral slices of less than one square centimeter were first prepared from apical branches of Stylophora pistillata colonies growing in aquarium conditions. The area of living tissue, number of polyps and photosynthetic pigments were quantified. In vivo biophysical measurements were carried out (yield of chlorophyll a fluorescence, P700 absorption changes, oxygen exchanges). From these measurements we concluded that photosystem II activity and respiratory rate of S. pistillata slices were very similar to those previously reported on whole nubbins measurements (Holcomb et al., 2014; Sorek and Levy, 2012). Photosystem I measurements gave also very stable signals, comparable to those obtained from green plants. We conclude that these results obtained on small fragments of corals are representatives of whole coral colony for biophysical analyses. Finally, these methodologies have been then applied on coral species (Pachyseris, Pocillopora, Porites sp.) sampled at two different sites of the Palau coral reef, which are exposed to different physico-chemical environments (pH and light intensity).