Effect of nutrient availability on understory algae during El Niño conditions at Central Pacific Baja California

Abstract

An experimental study of the effect of artificial nutrient supply on understory algae was made during 1997 El Niño Southern Oscillation (ENSO) at the Mexican Pacific coast of Baja California. Twelve quadrats of 1 m2 were placed on the sea bed. Six quadrats were used as controls, and six were treatments with added artificial nutrients. Nutrients were supplied using polyvinyl chloride (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 was tested using a multifactorial analysis of variance, and significant differences were obtained by post hoc Tukey’s HSD test. The analysis was carried out annually, seasonally, and seasonal and monthly for each species. The seawater temperature was recorded, and compared with historical data. The bottom and surface seawater nitrate concentration were measured. Twenty-five species of macroalgae and one seagrass were identified. The most abundant species was Corallina vancouveriensis (−N=19.8% and +N=26.6% average cover). The other species had lower than 10% cover. Significant differences of species percent cover between experimental groups (+N and −N) were detected in the annual analysis (p=0.059). Seasonal analysis did not showed significant differences for any season. Monthly analysis showed significant differences in average percent cover when nutrients were added in eight species in different months: Bossiella orbigniana (August); Colpomenia sinuosa (June); Corallina officinalis (August); C. vancouveriensis (June); Dictyota flabellata (September); Eisenia arborea (June); Gracilaria marcialaza (June); Macrocystis pyrifera (October), and the seagrass Phyllospadix torreyi (September and December). In conclusion, not all seaweed species are sensitive to nutrient addition during the ENSO years. In this research, we found eight species and one seagrass that had a positive reaction to the nutrients during the most severe stage (summer) of the ENSO.