Testing Hypotheses Linking Coarse Woody Habitat, Fish Populations, and Food Webs in Experimental Ecosystems

Coarse wood is a common littoral habitat in freshwater lakes and reservoirs throughout the world, however, the abundance of this habitat in many lentic systems is threatened by urban shoreline development as well as reservoir ageing. In this study, we tested four hypothesized mechanisms linking coarse woody habitat and fish populations by monitoring fish and food web responses across a gradient of coarse woody habitat addition in ten experimental ponds. Our results indicated a positive linear relationship between coarse woody habitat density and adult largemouth bass growth rates and reduced survival and of fish groups vulnerable to largemouth bass predation. We found no relationship between coarse wood density and growth of invertivorous fish or initial abundance of young-of-year largemouth bass or bluegills. Construction of food web models for each pond ecosystem indicated a minimal influence of coarse wood density on contribution of invertebrates to higher trophic levels whereas the indirect positive influence of largemouth bass predation on pelagic invertebrate biomass increased with coarse wood addition. Our results suggest that coarse woody habitat density may have the strongest influence on adult piscivorous fish energetics whereas the bottom up influence of this habitat on system-wide invertebrate production may be limited.