Laguna Ojo de Liebre is part of El Vizcaíno Biosphere's Reserve, one of the largest protected natural areas in the world. The contribution of seaweeds to the lagoons' total biomass had not been previously quantified. The purpose of this study was to evaluate the spatial and temporal variations of seaweed biomass in the lagoon. Seaweed samples were taken every season during 1995 at six sampling stations distributed throughout the lagoon. Total specific biomass of seaweeds was at its peak in the summer, and minimum in spring. The highest total annual biomass was found at Isla Brosa in the lagoon's central portion, and the lowest in El Dátil at the head. The seasonal and spatial variation of biomass in the lagoon is related with species richness and environmental parameters. Potentially important species in terms of biomass, wide spatial and temporal distribution, and potential use were: Spyridia filamentosa, Entheromorpha clathrata, Dasya baillouviana, Hypnea valentiaeand Sargassum sinicola .Using PCA three groups of stations were defined: one chiefly at the lagoon's mouth, another comprised the islands in the central portion, and the last in the lagoon's head
