AME 49:71-85 (2007)  -  DOI: https://doi.org/10.3354/ame01129

ABSTRACT: The present study investigated the use of indices based on variable chlorophyll fluorescence for the estimation of rates of photosynthesis by microphytobenthos. The relationship between fluorescence indices and photosynthesis, as measured on intact sediment samples, was studied (1) theoretically, using a simulation model to analyse the effects of light attenuation, biomass profile and depth integration, and (2) experimentally, by obtaining a comprehensive dataset of paired measurements of photosynthesis (oxygen microsensors) and fluorescence (PAM fluorometry) along hourly, 14 d and seasonal time scales, at 2 estuarine intertidal sites with distinctive sediment characteristics. Depth-integrated photosynthesis (P) was compared to EFY, an index based on depth-integrated fluorescence parameters estimating the productive biomass (minimum fluorescence, F₀) and the Photosystem II effective quantum yield (ΔF/F_m’). Whilst numerical simulations have indicated that the relationship between EFY and P can be conditioned by the vertical distribution of biomass, the experimental data showed EFY to closely trace variations in P in a wide range of light conditions, vertical distribution of productivity, sediment characteristics, and taxonomic composition of the microalgal community. A linear relationship between EFY and P was generally found, both when considering each day separately (significant correlations in 94.3% of the days) and when different days within each sampling period were pooled together (significant correlations in all cases). The slopes of the regression equations of EFY on P were found to vary throughout the year, indicating that the practical use of the index may require the frequent determination of conversion factors. Nevertheless, the use of this fluorescence index was confirmed to represent a valid methodology for the rapid and non-destructive estimation of photosynthetic rates in microphytobenthos.

KEY WORDS: Microphytobenthos · Photosynthesis · PAM fluorescence · Depth integration · Primary production · PSII electron transport · Benthic microalgae · Biofilms