The effect of fish predation on benthic community structure in streams

• Main Author: Rosenfeld, Jordan Stuart
• Format: Others
• Language: English
• Published: 2009
• Online Access: http://hdl.handle.net/2429/9588

The conditions under which fish have a large impact on benthic invertebrate community structure in streams are poorly defined. To better understand the mechanisms by which fish affect lotic invertebrate community structure, a series of experiments were performed in a fishless and fish-bearing stream in the University of British Columbia Malcolm Knapp Research Forest in the Coast Mountains of British Columbia. The first experiment examined the effect of predation by prickly sculpin (Cottus asper) and coho parr (Onchorhynchus kisutch) on invertebrates associated with tile and gravel substrate placed in enclosures installed in pools and riffles in fishless Mayfly Creek.. Effects of fish were most pronounced on tile substrate and in riffle habitat, and least pronounced on gravel substrate in pool habitat. Fish predation resulted in decreased density of larger-bodied (>6mm) herbivores (primarily the mayflies Ameletus and Baetis) and increased abundance of smaller (< 3mm) herbivorous invertebrates (primarily Orthocladiinae chironomids and nemourid stoneflies) and algae. The effects of fish predation in riffles in fish-bearing Jacobs Creek were similar to those observed in Mayfly Creek, except that there was no increase in algal biomass in the presence of fish. The indirect increase in algal biomass and density of small herbivores observed under fish predation was reproduced in experimental stream channels by excluding large invertebrate herbivores (tailed frog tadpoles (Ascaphus) and Ameletus), confirming that direct effects of fish on large-bodied grazers released algae and smaller herbivores from competitively dominant grazers. Manipulation of coho densities in upper enclosure sections in a fourth experiment indicated that upstream predation could have a small but measurable indirect effect on algal biomass in downstream patches. The abundance of detritivores in Mayfly and Jacobs Creek appear to be largely controlled by bottom-up forces (resource limitation), while herbivores are more strongly influenced by top-down effects (fish predation). A model for effects of fish predation on invertebrate community structure is proposed which predicts stronger predation effects in algal-based food chains than detrital-based food chains, both of which occur at a hierarchy of spatial scales in streams. === Science, Faculty of === Zoology, Department of === Graduate