Co-ocurrencia de Chattonella marina y Gymnodinium catenatum en la Bahía de La Paz, Golfo de California (primavera 2009)

During the period of 24 March to 14 May 2009, water and net samples were obtained for phytoplankton analyses; one aliquot was fixed in Lugol's solution for species quantification and identification. Net samples were used for the identification of live phytoplankton species. Additionally, temperature in situ, chlorophyll a and inorganic nutrients were measured weekly in three stations. Two species were identified: Chattonella marina (Subrahmanyan) Y. Hara et Chihara and Gymnodinium catenatum Graham. Chattonella marina was the most abundant species with a density at subsurface level of 14 × 10³ to 36 × 10³ cell L^-1. Gymnodinium catenatum had densities were of 1 × 10³ to 19 × 10³ cell L^-1. Water column temperature was quasi homogeneous from surface to 20 m in depth, with an interval of 19.5 to 22.0 °C and 20.0 to 21.5 °C from March to April respectively. In the middle of May stratification of the water column initiated with a slight temperature difference of 5.0 °C recorded from surface to 20 m in depth. Nitrates varied from 0.5 to 11.0 μM and orthophosphates from 0.4 to 2.6 μM. Chlorophyll a showed a value at surface level of 7.5 mg m^-3 and 3.5 mg m^-3 at 20 m in March; in May chlorophyll a values ranged between 2.0 to 7.0 mg m^-3. We conclude that the presence of these two species during this study period was associated to the relaxation of the mixing processes in the zone.