Coral reefs are known for their exceptional species diversity and productivity, yet are sensitive to biotic and abiotic perturbations. Many reefs have experienced phase shifts as the result of alterations in herbivore abundance. This research in Moorea, French Polynesia, is aimed at elucidating differential effects of sea urchin species on the coral reef community. Preliminary quantifications of benthic reef components suggest that the tropical echinoids Diadema savignyi, Echinothrix calamaris, Echinothrix diadema, Echinostrephus aciculatus and Echinometra mathaei influence the community on different scales, likely as a result of different feeding modes and grazing intensities. On a small, 25-cm2 scale, E. mathaei abundance was correlated positively with cover of crustose coralline algae (CCA), while E. aciculatus was associated with cover by algal turfs. On a larger scale (> 1 m2), it may be possible to predict reef community structure based on echinoid communities. The differential ability of the echinoids D. savignyi and E. mathaei to initiate a phase shift reversal on artificial reefs was tested by manipulating densities and compositions of these echinoid species on reefs dominated by the macroalgal species Sargassum pacificum. Macroalgal density was quantified over time. The reefs with D. savignyi underwent the greatest amount of algal loss due to herbivory and within two weeks macroalgal cover was decreased by greater than 10%. These results suggest that the herbivore D. savignyi may have the ability to alter community structure to a greater extent than E. mathaei. The results of this study may elucidate the ecological importance of species-specific interactions that shape reef communities and provide an additional basis for coral reef management strategies.