Phytoplankton photosynthetic parameters off Baja California: A tool to estimate primary production with remote sensing data

Phytoplankton photosynthetic parameters (maximum light utilization coefficient, alpha*; maximum photosynthetic rate, P*m; maximum quantum yield, phi-max) off Baja California were estimated from samples collected at the 50% light level during winter, spring, summer, and autumn 1999. Chlorophyll concentration was also determined, and in situ experiments were conducted using the 14C method to determine primary production (PP) in the euphotic zone. The highest alpha* and phi-max values were found during the spring survey, mainly at the coastal areas, associated with diatom and dinoflagellate abundances and high chlorophyll concentrations. However, high P*m values were measured during autumn in both inshore and offshore areas due to the presence of smaller phytoplankton cells. The average profiles of the photosynthetic parameters (alpha*(z) and P*m(z)) in the water column were estimated for 2 regions. These parameters were used to estimate PP with semi-analytical models. Modeled PP was contrasted with in situ PP to validate our calculated photosynthetic parameters in the euphotic zone. In general, modeled PP values were similar to in situ values (94 mg C·m–2·h–1), with a high correlation coefficient (r = 0.85). Modeled PP for coastal waters in the northern and central regions was 1.5-fold greater than in situ estimates during spring. In conclusion, when used with remotely sensed phytoplankton pigment and surface irradiance data, the average profiles of alpha* and P*m(z) could be a useful tool to calculate PP in our study area. Los parametros fotosinteticos (coeficiente de maxima utilizacion de la luz, alpha*; tasa fotosintetica maxima, P*m; eficiencia cuantica maxima, phi-max) fueron estimados para la region frente a Baja California a partir de muestras recolectadas del 50% de irradiancia superficial durante invierno, primavera, verano y otono de 1999. Ademas, se determino la concentracion de clorofila y se realizaron experimentos in situ para determinar la produccion primaria (PP) en la zona eufotica con el metodo 14C. Los valores mas altos de alpha* y phi-max se registraron durante la primavera, principalmente en la zona costera, y estuvieron relacionados con la abundancia de diatomeas y dinoflagelados y con las altas concentraciones de clorofila. Sin embargo, los valores altos de P*m se midieron durante el otono en la zona costera y la zona oceanica debido a la presencia de fitoplancton de menor tamano. Los perfiles promedio de los parametros fotosinteticos (alpha*(z) y P*m(z)) fueron estimados para la columna de agua en 2 regiones (norte y central). A partir de estos datos, se estimo la PP de ambas regiones oceanograficas usando modelos semi-analiticos. Para validar los parametros fotosinteticos calculados para la zona eufotica, la PP modelada se comparo con la PP in situ. En general, la PP modelada fue similar a los valores in situ (94 mg C·m–2·h–1), con un alto coeficiente de correlacion (r = 0.85). Se encontro que la PP modelada para aguas costeras de las regiones norte y central fue 1.5 veces mayor que la estimada in situ durante la primavera. Los resultados sugieren que, junto con informacion sobre pigmentos de fitoplancton y datos de irradiancia superficial medidos por sensores remotos, los perfiles promedio de alpha*(z) y P*m(z) pueden ser una herramienta util para calcular la PP en nuestra area de estudio.