The ecology of marine microbenthos IV. Structure and function of the benthic ecosystem, its chemical and physical factors and the microfauna commuities with special reference to the ciliated protozoa

Abstract The paper describes the ecosystem constituted by marine sediments and their microfiora and fauna but with special emphasis on the ecology of ciliated protozoa. This description is based on quantitative studies of the vertical and horizontal distribution of the fauna, the physicochemical factors (O2, H2, S, Eh, pH, grain size, organic matter, salinity) and the microfiora, and on model experiments with artificial and natural sediments. Factors controlling the oxidation-reduction properties of sediments, the O2-uptake of reduced sediments and the respiration and photosynthesis of undisturbed sediments were studied. Among other things it is demonstrated that the microfaunal communities can be correlated with the oxidation-reduction properties of sediments and with their mechanical composition and that the endproducts of anaerobic decomposition (notably H2S) are of large trophic significance to the sediment ecosystem through the activity of cherno- and photoautotrophic bacteria. The energetic role of the microfauna in sediments is estimated; mostly, the respiration of the microfauna exceeds that of the macrofauna. In fine and medium sands the ciliates constitute the most important group among the microfauna.