Contamination is a ubiquitous problem in the marine environment that has been observed to cause negative effects on multiple scales. Contamination may interact with other co-occurring stressors in natural systems further complicating the understanding of contaminant effects in the natural environment. Exposure to contamination via diet may also alter contaminant toxicity, due to varying uptake rates between different food sources. This thesis examines the effects of diet-borne contamination and other frequently encountered stressors, as well as their interactions, on herbivores that live on and consume macroalgae in near-shore rocky reefs. The relationship between temporal and spatial variation in macroalgal copper contamination and associated herbivore assemblages was assessed in a one-year field survey of Port Jackson (Sydney, Australia). Decreased herbivore abundance was associated with increased copper concentration; however, this relationship was only observed during peak abundance periods and was highly species-specific. The persistence of herbivores at even the most contaminated sites suggested the possibility of local adaptation and this was subsequently explored for an abundant herbivorous amphipod. Using a quantitative genetics approach genotypes from 8 locations were tested for copper tolerance. While many of the criteria for local adaptation were met, no evidence of local adaptation was found in this species. Copper toxicity is highly dependent on the species of macroalgae consumed, as indicated by a significant interaction between these two factors. A synergistic effect of exposure to copper contamination and temperature was observed at 26 ÂºC, with decreased amphipod survival observed. Exposure to algal secondary metabolites did not appear to interact with copper contamination; however the efflux transporter, P-glycoprotein, is a good candidate for the regulation of both chemical stressors. In summary algal-herbivore interactions are complex and driven by differential bioavailability of copper amongst macroalgal species. Persistence of herbivores at contaminated locations may be due to regulatory mechanisms such as P-glycoprotein however more research in this field is required.