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The effect of artificial nutrient supply on understory algae during 1997 El Niño at the Mexican Pacific coast of Baja California was studied. Twelve one square meter quadrats were placed on the sea bed. Six quadrats were used as control and six were used to add artificial nutrients. Nutrients were supplied using PVC pipes filled with slow-release inorganic fertilizer. The algae species composition and cover in each quadrat were estimated using the random point quadrat method. The percent of cover by group was tested with an analysis of variance. The seawater temperature was recorded, and compared with historical data. The bottom and surface seawater nitrate concentration were measured. Tissue nitrogen concentration (%) was determined for Eisenia arborea. Twenty six species of macroalgae and one seagrass were identified. The most abundant species was Corallina vancouveriensis (30% cover). The other species had lower than 10% cover. No significant differences of species percent cover between experimental groups was detected. In a second statistical analysis, we compared the average cover of the three most abundant species in the quadrats with nutrients versus the same species in the control quadrats for each month. Significant higher cover was obtained when nutrients were added for: Corallina vancouveriensis (June and December); Colpomenia sinuosa and Eisenia arborea (June); Corallina officinalis (August); Dictyota flabellata (September); Macrocystis pyrifera (October), and the seagrass Phyllospadix torreyi (September and December). Only six species and one seagrass were able to store and use artificial nutrients under high temperature-low nutrient conditions.

Palabras clave: Macrocystis; nutrients; El Niño; Temperature; Pacific; undestory algae

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