Primary production and photosynthetic efficiency in alfonso basin, La paz bay, Gulf of california, Mexico

Quantification of photosynthetic efficiency and productive capacity of the phytoplankton community was the objective of the surveys that were conducted in December 2005, May and August 2006; and February, May and November 2007 in Bahía de La Paz (Cuenca Alfonso). Samples of water were collected from 7 levels of surface irradiance (100, 55, 33, 10, 3, 1 and 0.1%), of the euphotic zone (Zeu). In situ primary production estimations were performed by 14C assimilation methodology. There were 2 basic assimilation ratios patterns; one with subsurface maxima during February and May 2007 and other with a tendency of increasing values as the lower limit of the Zeu was approached (December 2005; May and August 2006; November 2007). Minimum values were observed in December with a range of 0.16 to 2.35 mg C (mg Chla)-1 h-1. February 2007 showed high variability with a range of 3.3 to 22.4 mg C (mg Chla)-1 h-1. During December 2005, May, August 2006 and November 2007, there was an increase to 0.1% of surface irradiance, which reached 10.22 mg C (mg Chla)-1 h-1 in August 2006. In May 2007, the maximum value (13.23 mg C (mg Chla)-1 h-1 was associated with the mixing layer. Depth integrated primary production (PP) value up to 350 g C m-2 year-1 point out the high productive feature of the study site in Bahía de La Paz. A significant increase in the PP to consider 0.1% of the surface irradiance as the lower limit euphotic observed.