The influence of grazing by Hypogastrura viatica (Insecta: Collembola) on microbial activity in decomposing kelp on Spitsbergen

The influence of three different grazing levels (5-20 ind.) by Hypogastrura viarica (Collembola) on microbial activity in a Spitsbergen kelp Laminaria has been evaluated during a 10 day laboratoly experiment under oxic conditions. Respiration has been measured by infra-red gas analysis in the form of CO­2-emissions. The total and metabolically active fungal and bacterial biomass has been estimated by direct microscopical counts and epifluorescence techniques. Despite the results of other similar experiments, an increase in microbial numbers and biomass was recorded following the introduction of grazing. Grazing increases the mean respiration between 0.6 to 1.4 times. A corresponding increase in the microbial biomasses was also recorded. Although a trend towards decreased mean bacterial cell size was found, the fungi were more influenced by grazing than the bacteria. Bacteria constituted the predominant part of the microbial biomass in all the experimental vessels. The results indicate that Collembola plays an important functional role by regulating the microbial activity, probably by nutrient mobilization