ENSO, El Niño Southern Oscillation, generally manifests two stages in the tropical eastern Pacific, a warm, stormy, wet, high sea level phase, and a cool, calm, dry, low sea level phase. An immediate stressful period with coral bleaching and mortality occurs soon after the influx of El Niño elevated sea temperatures. Variable coral colony bleaching is due to the presence or absence of thermally tolerant dinoflagellate endosymbionts (e.g., Durusdinium). Millepora fire corals are susceptible to high temperature stress; two of three species experienced local extinctions. Symbiotic crustaceans decreased markedly in abundance with the loss of their coral habitat niche and food source. The loss of protective barriers of coral crustacean guards exposed massive corals to Acanthaster predation, resulting in partial mortality. Sea urchin population increases in Panama (Diadema) and the Galápagos Islands (Eucidaris), following El Niño elevated temperatures that initiated coral mortality, resulted in severe reef bioerosion that caused significant reef framework degradation. Patch reefs in the southern Galápagos Islands disappeared; extreme sea urchin bioerosion transformed coral colonies into sediments. Community wide changes in trophic resource utilization by reef fish feeding guilds (facultative corallivores, mixed diet feeders, and benthic invertivores) during post El Niño impacts are discussed in relation to coral recovery, topographic complexity, and availability of prey. Extreme and prolonged El Niño high temperature conditions depress or inhibit coral reproduction. La Niña cool conditions, with possible exceptions (depending on nutrient availability) inhibit coral reproductive activity.