Cycling of carbon and oxygen in layers of marine microphytes; a simulation model and its eco-physiological implications.

A mathematical simulation model was used to ascertain the relation between the diffusion of oxygen and inorganic carbon into layers of marine microphytes and the carbon metabolism of these microphytes. The simulation model included physiological and physico-chemical parameters and was validated using the few data available from the literature on production determinations, on oxygen and pH values, and on growth dynamics of natural populations. The model was tested with various modifications to mimic experiments with suspended algae and algal films on inert substrates, and also to simulate microphytobenthos in sediment cores with or without grazing. The simulated variations in oxygen concentrations and pH values over time scales of min and days were consistent with field and experimental observations. The model predicted upper limits of primary production and biomass observed in well developed natural populations; these limits are caused by a combination of oxygen accumulation and depletion of inorganic carbon resulting from diffusion limitations and the recirculation of organic carbon in photosynthetic, respiratory and excretory processes. The model calculations were used to check on the adequacy of the various methods used to determine the primary production of benthic microphytes.