LACK OF SEVERE NUTRIENT LIMITATION IN CAULERPA-TAXIFOLIA (VAHL) AGARDH, C, AN INTRODUCED SEAWEED SPREADING OVER THE OLIGOTROPHIC NORTHWESTERN MEDITERRANEAN

We performed a seasonal study of the importance of nitrogen (N) and ph osphorus (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 res pond 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 con trol plants. Rates of APA ranged from 9 to 52 mu M PO4 odw h(-1), clos e to those characteristic of P-sufficient macroalgae. Tissue nutrient concentrations were frequently above typical critical levels for speci es 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 con sistent. The lack of severe nutrient limitation in Mediterranean popul ations of Caulerpa taxifolia could be an important factor enabling it to outcompete native macrophytes.