Physiological versus behavioral photoprotection in intertidal epipelic and epipsammic benthic diatom communities

Physiological and behavioral photoprotection are the two major mechanisms by which natural microphytobenthic assemblages protect themselves against high light. These mechanisms were investigated with high vertical resolution in intertidal epipelic (mud) and epipsammic (sand) benthic diatom communities. Photophobic cell migration was found in epipelic communities when exposed to high light, detected using pigment analysis of 200 μm sediment depth layers and Low Temperature Scanning Electron Microscopy. In the mud, significant differences between migratory and non-migratory (Latrunculin A-treated) biofilms were observed in the photosynthetic activity measured using rapid light curves: after exposure to high light, non-migratory biofilms showed lower light use efficiency (lower α) and lower maximum photosynthetic capacity (lower rETRmax). Increased de-epoxidation state (DPS) was observed in both epipelic and epipsammic diatom assemblages after exposure to high light: in the surface 400 μm for mud and throughout the sediment profile up to 1 mm for sand. The two diatom communities showed different photoregulatory strategies: the epipelic community of muddy sediments photoregulated using both physiological and behavioral photoprotection, while the epipsammic community of sandy sediments used exclusively physiological mechanisms.

► We investigated photoprotection with high vertical resolution in benthic biofilms.
► Photophobic cell migration was found in epipelic diatoms: behavioral photoprotection.
► Non-migratory biofilms showed lower photosynthetic efficiencies under high light.
► Physiological photoprotection was found in both epipelic and epipsammic communities.
► The two diatom communities showed different photoregulatory strategies.