Compared to the well documented responses of lake pelagic communities to common anthropogenic influences, much less is known about potential responses by benthic communities. Concepts of how benthic and pelagic communities might interact and modify overall lake ecosystem responses to human influences on lakes such as nutrient loading or alteration of fish assemblages are also poorly developed, because benthic and pelagic communities are typically studied in isolation by benthic or pelagic ecologists. This dissertation focuses on how whole lake manipulations of nutrient loading rates and fish assemblages shape the mechanisms and properties linking benthic and pelagic habitats and communities in experimental lakes over a five year period.

Water column nutrient enrichment to 2000L in situ experimental mesocosms over a nine-week period produced increases in the density, mean individual mass, and emergence of benthos. Nutrient enrichment also affected the taxonomic composition of benthos associated with sediments and epiphytes. Benthic responses to nutrient enrichment to whole lakes over several years produced less dramatic results, and differed between depths. The biomass of littoral benthos varied little among ambient and enriched lake states, and was not positively related to epilimnetic phytoplankton abundance, or light intensity, which limits benthic algal production. Metalimnetic benthic biomass was more varied among lake trophic states, and was positively related to both phytoplankton abundance and light intensity in the metalimnion. Carbon
pathways to benthos were also affected by lake fertilization.

This dissertation also addresses the hypothesis that size-selective predation is the primary mechanism by which fish influence benthic community structure. I used a fish bioenergetics model and normalized size spectra to demonstrate that fish consumption rates on benthos were strongly related to the taxonomically-independent size distribution of benthic prey. Benthos size-structure was more variable in the absence of high consumption rates by fish. Comparisons of selectivity supported the finding that fish select benthic prey largely based on differences in body size among benthic taxa, but taxon-specific and size-independent factors also influence selectivity of fish on benthos to a lesser degree.