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

Spatial variability of the central Gulf of California (CGC) phytoplankton b iomass and photosynthetic parameters in relation to physical forcing was st udied. Sampling was carried out in November, and the surface T degrees C ra nge was 20-27.5 degrees C. Strong tidal mixing in the midrift islands regio n injects relatively cool, nutrient-rich waters to the euphotic zone. Some of this water is transported via jets and cool filaments throughout the Gul f. In general, chlorophyll a (Chl) of small phytoplankton (<8 mu m) (up to >2.5 mg m(-3)) was higher than that of large phytoplankton. Highest values of phytoplankton assimilation numbers (P(B)m) [3.17 mg C (mg Chi a)(-1) h(- 1)], and photosynthetic efficiency (alpha(B)) [0.23 mg C (mg Chi a)(-1) h(- 1) (W m(-2))(-1)] were determined for the large phytoplankton cells (>8 mu m). Our hypothesis that P(B)m values increase from cooler to warmer waters is not supported by the data. We found a 27-fold spatial difference of Chi, compared with a 10-fold difference of P(B)m and a 6-fold difference of alp ha(B). Thus, in our study area, the major source of variability for primary productivity (PP) comes from Chi, and not from P(B)m and alpha(B). Therefo re, we propose that it is possible to estimate late-fall PP for the CGC usi ng average photosynthetic parameters. Average values for P(B)m and alpha(B) of total phytoplankton were 0.72 mg C (mg Chi a)(-1) h(-1) and 0.12 mg C ( mg Chi a)(-1) h(-1) (W m(-2))(-1), with standard errors of 0.07 and 0.03, r espectively.