We performed a seasonal study of the importance of nitrogen (N) and phosphorus (P) as limitation to the productivity of Caulerpa taxifolia (Vahl) C. Agardh, a seaweed invading the western Mediterranean coasts. The study presented here indicates that Caulerpa taxifolia did not respond to nutrient enrichment, except for plants collected in April and September 1993, where productivity and alkaline phosphatase activity (APA) of enriched plants varied 0.5- to 3-fold relative to those of control plants. Rates of APA ranged from 9 to 52 mu M PO4 odw h(-1), close to those characteristic of P-sufficient macroalgae. Tissue nutrient concentrations were frequently above typical critical levels for species of macroalgae ranging from 1.36 to 3.13% dw, and 0.16 to 0.21% dw, for N and P, respectively. Seasonal variation was moderate and not consistent. The lack of severe nutrient limitation in Mediterranean populations of Caulerpa taxifolia could be an important factor enabling it to outcompete native macrophytes