Photo-regulation in microphytobenthos from intertidal mudflats and non-tidal coastal shallows

Abstract : The study investigated seasonal changes in the photo-regulatory mechanisms of microphytobenthosfound in intertidal mudflats (Aiguillon Bay, the Atlantic, France) and non-tidal sandy coastal shallows(Puck Bay, the Baltic, Poland) based on photosynthetic pigment characteristics and the estimates ofphotosynthetic parameters obtained through oxygen evolution measurements. The intertidal communitiesconsisted of motile diatom species typical of epipelon. The non-tidal microphytobenthos wascomposed of epipsammic species mostly belonging to four taxonomic groups chiefly contributing to theassemblage biomass, namely cyanobacteria, euglenophytes, green algae and diatoms (comprising mainlysmall-sized species). The epipelon was low light acclimated as shown by the lower values of photoprotective/photosynthetic (PPC/PSC) carotenoids and diatoxanthin/diadinoxanthin (Dt/Dd) ratios. Incontrast, the epipsammon exhibited features of high light acclimation (high PPC/PSC and Dt/Dd ratios). Inboth microphytobenthos types, the photosynthetic capacity (Pm) showed the same seasonal variationpattern and there were no statistically significant differences between the investigated sites in correspondingseasons (P > 0.05). In both assemblage types, the photosynthetic efficiency at limiting irradiance(a) decreased over time. The epipelon had higher a compared to the epipsammon. Seasonal changesof the photoacclimation index (Ek) estimated for the epipelic communities reflected variations observedin Pm, whereas in the epipsammon an increasing trend in Ek values was observed. Ek was always higherfor the epipsammon when comparing analogous seasons, which further corroborated low and high lightacclimation in the epipelic and epipsammic communities, respectively. The presence of the photoinhibitionparameter (b) in the epipelon and the lack of it in the epipsammon suggested that the latterwas resistant to high irradiance and the physiological mechanisms were sufficient to protect it fromphotoinhibition. In the epipelon, a downturn in photosynthetic rates showed that it was susceptible tohigh light intensities, suggesting that physiological photoprotective mechanisms must be supported bybehavioural photoacclimation in order to avoid damaging light influence.
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Filip Pniewski, Paulina Biskup, Iwona Bubak, Pierre Richard, Adam Latala, et al.. Photo-regulation in microphytobenthos from intertidal mudflats and non-tidal coastal shallows. Estuarine, Coastal and Shelf Science, Elsevier, 2015, pp.153-161. ⟨10.1016/j.ecss.2014.11.022⟩. ⟨hal-01096631⟩

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