Spatial variability of the photosynthetic parameters and biomass of the Gulf of California phytoplankton

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Abstract
Spatial variability of the central Gulf of California (CGC) phytoplankton biomass and photosynthetic parameters in relation to physical forcing was studied. Sampling was carried out in November, and the surfaceTC range was 20-27.5°C. Strong tidal mixing in the midrift islands regions injects relatively cool, nutrient-rich waters to the euphotic zone. Some of this water is transported via jets and cool filaments throughout the Gulf. In general, chlorophyll a (Chl) of small phytoplankton (m) (up to >2.5 mg m-3) was higher than that of large phytoplankton. Highest values of phytoplankton assimilation numbers (P&Bgr;m) [3.17 mg C (mg Chla)-1 h-1], and photosynthetic efficiency &Bgr;) [0.23 mg C (mg Chl a)-1 h-1 (W m-2)-1] were determined for the large phytoplankton cells (>8 &mgr;m). Our hypothesis thatP&Bgr;m values increase from cooler to warmer waters is not supported by the data. We found a 27-fold spatial difference of Chl, compared with a 10-fold difference ofP&Bgr;m and a 6-fold difference of &agr;&Bgr;. Thus, in our study area, the major source of variability for primary productivity (PP) comes from Chl, and not fromP&Bgr;m and&agr;&Bgr;. Therefore, we propose that it is possible to estimate late-fall PP for the CGC using average photosynthetic parameters. Average values forP&Bgr;m and&agr;&Bgr; of total phytoplankton were 0.72 mg c (mg Chl a)-1 h-1 and 0.12 mg C (mg Chla-1 h-1, (W m-2)-1, with standard errors of 0.07 and 0.03, respectively.

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