Free-living nematodes affect oxygen turnover of artificial diatom biofilms

The aim of the present study was to examine the effects of biofilm-dwelling nematode activity on the oxygen turnover of cultured diatom biofilms. Oxygen microprofiles were simultaneously measured using the microelectrode technique in biofilms incubated with and without nematodes during short-term (24 h) and medium-term (6 d) experiments. During 24 h nycthemeral incubations, maximum oxygen concentrations and oxygen peak depths of microprofiles, as well as net oxygen production rates, were significantly higher in the diatom biofilms with nematodes. These effects might be dependent on the densities of nematodes. In the present study, significant effects were observed at nematode densities exceeding 100 ind. cm(-2), but not at a density <50 ind. cm(-2). During 6 d incubations, net oxygen production in the photic zone was significantly higher in biofilm containing meiofauna than in biofilms without meiofauna. The processes involved are discussed. The short-term experiment simulates a disturbance of a lotic diatom biofilm as would be induced by a sudden colonisation of nematode populations. The question remains whether a long-term occurrence of nematodes in the biofilm would also result in an increased productivity rate. A first indication of a persistent increase in net productivity related to the continuous presence of nematodes is provided by the 6 d incubation experiment.