Relatively few species compared with other coral reef regions characterized eastern Pacific reef ecosystems. Nonetheless, all ecological functional groups necessary for coral reef formation, growth, and persistence are represented. These include reef building corals and crustose coralline algae, symbiotic zooxanthellae, reef fishes and invertebrates of diverse trophic guilds and ecological functions. Visual surveys, baited traps, and artificial reef structures were employed to help assess coral community diversity. Reported estimates of species richness are: (a) zooxanthellate scleractinian and Millepora hydrocorals, ~50 species; (b) symbiotic zooxanthellae, 15 genera, 100 s of species; (c) coral reef fishes, ~500 species; (d) motile cryptic invertebrates, ~290 species. Eastern Pacific reef-building corals and many reef-associated invertebrates and fishes are of Indo-Pacific origin, with virtually no species shared with Caribbean coral reefs. Numerous cryptic metazoan predators likely strongly influence species attempting to recruit and shelter in Pocillopora reef communities. These groups vary greatly in abundance during present day coral mortality and reef degradation. How such changes affect biodiversity, ecological functions, and coral reef survival need urgent study.