Effects of stream grazers with different functional traits on the spatial heterogeneity of periphyton mats

BACKGROUND: Grazing activity on periphytic mats determines mat structure and spatial heterogeneity. Spatial complexity in stream periphyton is highly divergent and may depend on the functional traits of the different primary consumers species (i.e., grazers) such as mouthpart morphology, feeding behavior, and feeding activity. We evaluated the effect of grazing by three species having different functional traits on periphytic mat structure with a focus on mohthpart morphology. METHODS: An enclosure experiment was conducted in a stream located in the Nara Prefecture of Japan using two caddisflies with scraping mouthparts, Micrasema quadriloba and Glossosoma, and one mayfly, Epeorus, with brushing mouthparts. The spatial heterogeneity of chlorophyll a(Chl a) was evaluated, and the periphytic mat was analyzed using scanning electron microscopy (SEM) after a 12-d feeding experiment. RESULTS: Our results showed the differences in the spatial heterogeneity of the periphytic mats, such as differences in Chl a levels, grazed by the different grazing species. The strongest effect on the spatial heterogeneity and periphytic abundance was observed for Micrasema quadriloba, a caddisfly species with scraping mouthparts. Epeorus mayfly, with brushing mouthparts and high-mobility behavior, produced the weakest effect on spatial heterogeneity. Glossosoma caddisflies had moderate effects on periphytic spatial heterogeneity and abundance. Our results suggest that differences in grazing effects are largely dependent on grazer mouthparts and behavior.