Radiative energy budgets of migrational microphytobenthic biofilms

Abstract

Epipelic, biofilm-forming diatoms are key drivers of the primary production of mudflats. Such primary production is strongly affected by the vertical migration of diatoms, which is modulated by diurnal photoperiods, tidal cycles, and photoprotection mechanisms. However, the role of vertical migration in the radiative energy budget (REB) of microphytobenthic biofilms remains largely unknown. Here we used microsensor measurements of temperature and O2 in combination with reflectance spectroscopy and variable chlorophyll fluorimetry to construct the REB of intertidal, epipelic diatom-dominated biofilms for different emersion times (1, 3 and 5 h after the beginning of the in-situ emersion) and photon irradiance regimes, i.e., 400 and 800 µmol photon m−2 s−1. The effect of migration on REBs was studied by inhibiting diatom motility with Latrunculin A (Lat-A). Photosynthetic activity and light utilization efficiency decreased slightly, after adding Lat-A, while the amount of reflected light energy remained constant at ~ 23% of the incident irradiance and the majority (76–78%) of the incident light energy was dissipated as heat. Of the energy dissipated as heat, < 24% was dissipated upward in Lat-A treated samples, while an increasing downward heat dissipation was observed in Lat-A treated samples, as compared to control samples under an irradiance of 800 µmol photon m−2 s−1. However, we found no statistical significant differences in the REB and physiological parameters in the different treatments. Thus, we did not find any evidence that vertical migration of diatoms affected photosynthesis and light efficiency in the microphytobenthic biofilm over an emersion cycle, and a clear effect of non-photochemical quenching in REB and heat dissipation fluxes was not observed.