PARENT SESSION
Contributed Oral Session 10: Aquatic Trophic Systems I
Monday, August 8, 8:00 AM - 11:30 AM, Meeting Room 519 B, Level 5, Palais des congrès de Montréal

Trophic flows across ecosystems: Relationships among terrestrial invertebrate inputs, fish growth, and benthic invertebrate communities.

Zhang, Yixin^{*,1, 2}, Richardson, John¹, ¹ University of British Columbia, Vancouver, BC, Canada² University of Hong Kong, Hong Kong, P. R. China

ABSTRACT- Ecologists have long been interested in understanding the trophic flows across ecosystems and their effects on populations and communities in local habitats. We conducted a large-scale field experiment for investigating how terrestrial invertebrate input (TI) to influence resident cutthroat trout growth, and their effects on benthic invertebrate communities in two headwater streams with different levels of habitat heterogeneity and different riparian forest covers. East Creek with the low variation of substrate composition had a deciduous riparian canopy. Spring Creek, with a high level of substrate heterogeneity possessing lots of large woody debris, had a mature coniferous canopy. Two factorial experimental factors were fish (present or absent), and TI (reduced by two 25-m long greenhouse canopies at each stream or nature in controls). The average TI at East Creek with a deciduous riparian canopy was 2.4 fold higher than that at Spring Creek in a coniferous forest during the experimental period. TI experimental reduction did not significantly influence fish growth in either stream. However, there was a trend that fish growth was reduced in both streams under TI reduction in contrast to the controls. In East Creek, both fish and TI reduction had significant effects on benthic invertebrate biomass. When food-resource availability changed, cutthroat trout shifted foraging mode from drift feeding to benthic feeding for obtaining available food resource in a local habitat. The mechanism of such foraging-mode shift was demonstrated by a small-scale mesocosm experiment in artificial stream channels in East Creek. In Spring Creek, in contrast, there was no significant treatment effect on benthic invertebrate biomass, which may be because of low TI and a high level of habitat heterogeneity with a large amount of large woody debris in the stream channel that benefited benthic invertebrate communities. This study suggests that TI during summer may be a seasonal subsidy for cutthroat trout, but not an essential food resource for supporting cutthroat population growth in these streams with different riparian forest canopies.

Key words: Trophic flows, cutthroat trout, growth, invertebrate communities