Coral Photosynthesis & Ecophysiology

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Photosynthetic micro-organisms like microalgae and cyanobacteria are vital primary producers, contributing to 45% of global carbon fixation. Studying microalgae in corals helps unravel key factors influencing coral photosynthesis. Experimental techniques, including oxygen production and chlorophyll fluorescence measurements, along with oxygen microsensors, aid in characterizing aquatic photosynthesis in benthic habitats.

Microsensors

Microsensors are powerful tools to study the physiology of microorganisms in their natural habitat because of their small sensing tips (usually <100 micrometer) that faciliatate measurements at high spatial and temporal resolution. There is a wide range of microsensors that can measure various chemical species and physical parameters (e.g. light and temperature). The image to the left shows combined measurements of light and oxygen on a coral reef during low tide.

Pulse-amplitude modulated fluorimetry allows for a rapid determination of photosynthetic parameters, non-invasively, in situ and during ambient fluctuating light. PAM measurements rely on chl a fluorescence (i.e. 660-760 nm) of photosystem II. PAM allows for calculating the proportion of photochemistry and heat dissipation through quenching analysis of a sample in dark and light adapted states. The image above shows the distribution of the maximum quantum yield of PSII over a coral surface.

PAM Fluorimetry

Related Publications:

Kramer N, Tamir R, Ben-Zvi O, Jacques SL, Loya Y & Wangpraseurt D*, 2021. Efficient light harvesting in mesophotic corals is facilitated by coral optical traits (Functional Ecology)

Brodersen, K.E., Lichtenberg, M., Ralph, P.J., Kühl, M. and Wangpraseurt, D., 2014. Radiative energy budget reveals high photosynthetic efficiency in symbiont-bearing corals. Journal of the Royal Society Interface, 11(93), p.20130997.

Revsbech, N.P., 1989. An oxygen microsensor with a guard cathode. Limnology and Oceanography, 34(2), pp.474-478.

Schreiber, U., 2004. Pulse-amplitude-modulation (PAM) fluorometry and saturation pulse method: an overview. Chlorophyll a Fluorescence, pp.279-319.

Suggett, D.J., Prášil, O. and Borowitzka, M.A., 2010. Chlorophyll a fluorescence in aquatic sciences: methods and applications (pp. 427-433). Dordrecht, The Netherlands: Springer.

Wangpraseurt, D., Polerecky, L., Larkum, A.W., Ralph, P.J., Nielsen, D.A., Pernice, M. and Kühl, M., 2014. The in situ light microenvironment of corals. Limnology and Oceanography, 59(3), pp.917-926.