Resumen

HERNANDEZ-BECERRIL, David Uriel  y  PASTEN-MIRANDA, Norberto. Abundance and distribution of the picoplanktonic cyanobacteria Synechococcus in La Paz bay and Carmen basin, Gulf of California (June, 2001). Hidrobiológica [online]. 2015, vol.25, n.3, pp.357-364. ISSN 0188-8897.

Picophytoplankton, the smallest fraction of the marine phytoplankton (sizes between 0.2 and 2 μm), has recently become very important, due to its unexplored diversity and relevance in the pelagic realm. During an oceanographic cruise carried out from 21 to 26 June, 2001 in the Gulf of California, hydrographic variables were measured and samples to study planktonic cyanobacteria were collected, from six stations in two different zones, Bahía de La Paz and Cuenca Carmen. Observations made by epifluorescence microscopy showed the presence of Synechococcus, and cell counts were performed to calculate absolute abundances, which varied from 9.1 X 104 to 7.7 X 107 cells L-1, with a general average of 7.78 X 106 cells L-1. These values are comparable with those found in the world literature. Hydrographic conditions in summer at the stations of the Bahía de La Paz indicated well-defined stratification of the water column, with surface main thermoclines (10-15 m), whereas the vertical distributions of Synechococcus abundances showed marked peaks of maximum abundances at subsurface (20-30 m), and other deeper peaks (50-60 m) with lower cell densities. This suggests the development of Synechococcus populations with contrasting ecophysiological characteristics: differential adaptations to intensity and quality of light, and to nutrient concentrations, in two layers, subsurface and deeper. In Cuenca Carmen, with similar hydrographic conditions, but higher surface temperatures, the vertical distributions of Synechococcus were different, one distribution showing a gradual abundance decrement with depth and one having a relative homogeneous distribution.

Palabras llave : Cyanobacteria; Gulf of California; picoplankton; Synechococcus; vertical distribution.