Abundance of coccoid cyanobacteria, hydrographic parameters and the possible underestimation of in situ chlorophyll a in the northern gulf of California and the Mexican California Current

Abstract

The abundance of coccoid cyanobacteria was counted within the euphotic zone at a station in Delfín Basin, in the northern Gulf of California, and at a station in the California Current, off Todos Santos Bay, during 1993. The abundance of cyanobacteria at both stations was between 10⁷ and 10⁸ cells L^–1. Comparison with other concomitantly sampled parameters, i.e., irradiance, temperature, nutrients and chlorophyll a, showed no significant correlation with the cyanobacterial abundance. The contribution of cyanobacteria to the total in situ chlorophyll a concentration was calculated using the cyanobacterial abundance, an average published value of 1.0fgChl a cell^–1 and a reduced pigment extraction efficiency in cyanobacteria. Cyanobacteria contributed, in half of the cases, more than 10% and more than 4% of the total chlorophyll in Delfín Basin and the California Current, respectively. Again, this relative contribution was not related to the other concomitantly measured in situ parameters. In Synechococcus (WH-7803) cultures, the cellular chlorophyll a concentration was measured after extraction by soaking the samples in different solvents: 90% acetone and dimethylsulfoxide/acetone/water (DMSO/acetone). The cellular chlorophyll of WH-7803 extracted with DMSO/acetone was a factor of 1.9 times higher than the cellular chlorophyll concentration extracted with 90% acetone without sonication. Assuming that only the cyanobacteria would yield higher chlorophyll concentrations with DMSO/acetone extraction, then the chlorophyll a concentrations measured with 90% acetone extraction without sonication underestimated, in half of the cases, the real concentrations of in situ chlorophyll a by more than 5% in the northern Gulf of California and more than 2% in the California Current.