Applications for DIVING-PAM-II

Photosynthesis under Extreme Conditions (Heron Island, Great Barrier Reef, Australia)

The DIVING-PAM-II was applied for the very first in situ measurements of spectral reflectance and photosynthetic activity of cyanobacterial biofilms colonizing the intertidal beachrock platform of Heron Island, Great Barrier Reef.

This is an extreme environment undergoing large changes in temperature (28->50 degrees Celsius), light exposure (high UV and PAR levels of > 2000 µmol photons m-2 s-1), salinity (freshwater to >50 ppt salinity) and water status (dry to fully submersed) on a daily basis, as driven by the local tides on Heron Island.

The spectrometer of the DIVING PAMII enabled us to study the distribution of different cyanobacteria via measurements of reflectance spectra on different locations on the beachrock in combination with measurements of light acclimation of the beachrock cyanobacteria under different tidal conditions, which are impossible to simulate in the lab.

Our spectral reflectance measurements showed that the beachrock harbors a dense cyanobacterial biofilm community, which is shielded against UV and bright sunlight via high levels of protective sunscreens (scytonemin and carotenoids). This enables efficient photosynthesis even under extreme conditions, as quantified via in situ measurements of rapid light curves on the beachrock platform.

Professor Michael Kuhl, University of Copenhagen