Abstract

The effect of nutrient availability on Macrocystis pyrifera recruitment and survival of juvenile sporophytes was examined at its southern limit off Baja California, Mexico. Nitrate levels were inversely correlated with water temperature (r² = 0.70) at the experimental location. Low concentrations of nitrate occurred during most of 1998 (< 3 μM) except in spring (4.8–18.8 μM ). Experimental seeding with sporophylls and fertilizing the plants with a slow-release inorganic fertilizer produced successful recruitment when the water temperature was declining (18.7 °C). Survival of transplanted juveniles was significantly higher when fertilized during a period of particularly warm water and low nutrients in 1998 caused by El Niño. Analysis of tissue nitrogen suggests that plants were nutrient-limited during this period, and possibly affected synergistically by temperature stress. The results indicate that nutrients directly affect recruitment and survival of giant kelp at its southern limit, particularly during El Niño conditions.