Effect of nutrient availability on Macrocystis pyrifera recruitment and survival near its southern limit off Baja California

The effect of nutrient availability on Macrocystis pyrifera recruitment and survival of juvenile sporophytes was examined at its southern limit off Ba ja California, Mexico. Nitrate levels were inversely correlated with water temperature (r(2) = 0.70) at the experimental location. Low concentrations of nitrate occurred during most of 1998 (< 3 muM) except in spring (4.8-18. 8 muM). Experimental seeding with sporophylls and fertilizing the plants wi th a slow-release inorganic fertilizer produced successful recruitment when the water temperature was declining (18.7 degreesC). Survival of transplan ted juveniles was significantly higher when fertilized during a period of p articularly warm water and low nutrients in 1998 caused by El Nino. Analysi s of tissue nitrogen suggests that plants were nutrient-limited during this period, and possibly affected synergistically by temperature stress. The r esults indicate that nutrients directly affect recruitment and survival of giant kelp at its southern limit, particularly during El Nino conditions.