Recruitment in Ulva blooms in relation to temperature, salinity and nutrients in a subtropical bay of the Gulf of California

Ulva blooms are highly productive ephemeral communities that occur in coastal systems, associated with nutrient enrichment. The objective was to estimate variations in succession, cover, recruitment and length of Ulva species in four blooms and assess their relationship with environmental parameters in Bahía de La Paz, Baja California Sur. At each locality, monthly samplings were performed to register the presence, recruitment, length and cover of species, and temperature, salinity, turbidity and nutrient concentration in surface seawater from February 2013 to October 2015. The species found were Ulva acanthophora, Ulva clathratha, Ulva intestinalis, Ulva flexuosa, Ulva lactuca, Ulva lobata, Ulva nematoidea and Ulva rigida. The Ulva blooms in Casa del Marino, San Juan de la Costa and El Tecolote were multi-species, with U. rigida displaying the highest presence, cover and recruitment, followed by U. acanthophora. Significant differences were found between localities, years and months for biological and environmental factors. A principal component analysis (PCA) revealed significant relationships between higher cover, recruitment and length with higher nutrients concentrations at San Juan de La Costa, Casa del Marino and El Tecolote, indicating favourable conditions that allowed rapid growth. The cover, recruitment and length of U. flexuosa at El Portugués were inversely correlated with temperature.