Dynamic behaviour of benthic microalgal biomass in intertidal mudflats

The dynamic behaviour of microphytobenthic biomass in a European intertidal mudflat has been analysed by comparing field and laboratory measurements. In an experimental mesocosm, where the effects of grazing by deposit-feeders and resuspension by tides had been significantly decreased, the benthic microalgal biomass followed a logistic-type growth curve, and thus converged towards a maximum value at which production is theoretically equal to zero. In the field, the kinetics of microalgal biomass—measured during 14 consecutive days at the beginning and at the end of every daytime exposures—exhibited a different pattern with biomass increases during daytime exposures and biomass decreases during the other periods, thus describing a series of oscillations. It is suggested that in the field, the effect of grazing and resuspension prevents biomass from holding steady at its maximum level. Moreover, it has been found a significant negative relationship which states that the higher the biomass level at the beginning of daytime exposures, the lower the net production during that daytime exposure. In other words, it turned out that in the field, the biomass also tends to converge towards a “field maximum” where net production is equal to zero. Taken together, these observations allow to hypothesize that the high productivity of the microphytobenthic community in intertidal mudflats is due to the tight coupling between physical and biological processes.