Linkage between microbial loop and grazing food chain in benthic environments of streams

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1. We determined vertical changes in flow velocity and dissolved oxygen saturation in biofilms on artificial and natural substrates using microelectrodes. Vertical profile of current velocity versus depth indicated a presence of viscous sublayer. Our results also suggest smoothness of substrate surface is related to vertical profile of DO saturation.2. Various measurements of microbial productivity in streambed pebble biofilms were analyzed almost monthly for one year to quantify the importance of primary production as an autochthonous source of organic matter utilized to support heterotrophic bacterial production in the dynamic food web within this natural microbial habitat. It is likely that both autochthonous and allochthonous supplies of organic matter are important for production of bacteria in the pebble biofilms that develop in rapidly flowing fresh water streams.3. We examined food selectivity on microalgae by aquatic insects in Hiji Steram, Ehime, whose main water source is a eutrophic reservoir, from July to August 2004. Our results suggest that Cheumatopsyche selectively grazes on Microcystis when the size of the colony is small, and that the insect shows selective grazing on some eukaryotic microalgae such as Pediastrum and Synedra.4. To test hypotheses relating the cue communication between periphyton and grazers, we performed two kinds of laboratory channel experiments using case-bearing caddisfly grazer (Glossosoma spp.) and microalgal cue. Although the selectivity to the particle cue (i.e., chemical scent and visual drifting microalgae) was higher than that of the dissolved cue (only chemical scent), the selectivity was also not significantly different between the particle and the dissolved cues. Thus, it was concluded that Glossosoma larvae were able to detect both the visual (i.e., drifted microalgae) and the chemical cues.