Ecological stoichiometry is based on the concept that the relative availability of chemical elements in the environment can affect their biological transformations. My doctoral research used this stoichiometric perspective to examine how the relative availability of light, dissolved inorganic carbon (DIC), and phosphorus (P) affects interactions between grazers and microalgal producers in littoral zones of boreal lakes. As such, I posed three main questions: 1) what is the extent of variation in C:P ratios of epilithon (organic matter attached to rock surfaces)?, 2) what factors contribute to this variability?, and 3) how does variation in epilithic C:P ratios affect growth and nutrient release by benthic grazers? Using eighteen years of historical data from the Experimental Lakes Area (ELA), Canada, I found extensive variation in the C:P ratios of epilithon equaling or exceeding the range described for other autotrophic communities. Analysis of this data showed that epilithic C:P ratios were negatively correlated with epilimnetic total P and positively related to DIC concentrations. These results suggest that benthic algal communities reduce rates of C-fixation relative to P-uptake as the ratio of DIC to P decreases. I tested this hypothesis with experiments that manipulated light, DIC, and P availability to colonizing benthic algal communities in two boreal lakes at the ELA. While P enrichment lowered epilithic C:P ratios on substrates, shading and C enrichment had no effects on epilithic C:P ratios. My results indicate that very high DIC:P and PAR:P supply ratios in these lakes result in the accumulation of high C:P organic matter consisting of both algal cells and exuded particulate organic matter. In fact, it appears that benthic microalgae exude significant amounts of C-rich and P-poor organic matter, which contributes to high C:P ratios found in natural epilithon. Another experiment manipulated the density of caddisflies grazing on natural epilithon to test how consumptive and nutrient excretion activities of grazers affects epilithic C:P ratios. I found highly grazed enclosures had epilithic C:P ratios nearly half of ungrazed enclosures but that changes in epilithic C:P ratios were not likely a direct result of changed algal cellular nutrient content. Instead, my results suggest that high rates of consumption by the caddisflies led to a shift from algal-derived to grazer-derived detritus and lower C:P ratios in the epilithon. Finally, a series of laboratory and field experiments examined potential effects of high epilithic C:P ratios on benthic grazer communities. Mayflies fed algae of high C:P ratios (600-800) grew significantly slower than those fed low C:P ratios (80) in a laboratory experiment. Similar results were found in experiments using animals and food collected at ELA. Mayflies fed P-enriched and naturally P-rich epilithon grew faster compared to those consuming unenriched, naturally P-poor epilithon. These results indicate that littoral zone food webs are strongly affected by elemental imbalances at the grazer-producer interface. Thus, future research should consider whether and how stoichiometric differences between trophic levels affect organismal and ecosystem-level processes in benthic ecosystems.