The trophic role of red grouper (Epinephelus morio) on the northern continental shelf of Yucatan, Mexico, is analyzed through simulated changes in its biomass, based on a previous study using the ECOPATH model and which emphasized the commercially important fish resources. Red groupers occupy a high trophic level in the ecosystem, together with mojarras, king mackerels, snappers, sharks and octopuses. Except for the octopus, all others can be grouped as a single box in the model without loss of structural information. When decreases in biomass of red groupers were simulated, the contributions to detritus from primary producers and the sum of all exportations increased, along with other commercially important groups of fishes such as snappers, majorras, king mackerels and sharks. Net primary production, sum of flows for respiration, the sum of all consumptions and ascendencies decreased, along with the biomasses of sea trouts and sardines. In general terms, observed changes result in the ecosystem maintaining its thermodynamic equilibrium.