DISTRIBUTION AND ABUNDANCE OF DIATOMS OF THE GENUS PSEUDO-NITZSCHIA IN EL NIÑO CONDITIONS IN 2007 IN THE COLOMBIAN PACIFIC BASIN

Abstract

The spatial distribution and abundance of diatoms belonging to the genus Pseudo-nitzschia in the Colombian Pacific Basin (CPB) during PACÍFICO XLIV- ERFEN XLII oceanographic survey is described, whereas its relation to temperature and salinity was tested. Samplings of phytoplankton (Niskin bottles 5 L) at two depths (surface and 50 m deep) were carried out in 25 stations. The highest abundances of Pseudo-nitzschia were observed at surface, especially clustered in the intermediate CPB zone. This spatial pattern agreed with low temperature and high salinity values. Consistent with previous data, there were significant differences in the abundance of Pseudo-nitzschia between the two depths sampled (Mann-Whitney test, p = 0.001). A direct relationship between salinity and the genus abundance was set (r = 0.50; p = 0.01), indicating the affinity of these algae to environments with high salinities, whereas an inverse trend was showed with the temperature (r = -0.42; p = 0.043). Although the correlation values are not high, the spatial distribution of biotic and abiotic variables, suggest the influence of salinity and temperature on the abundance and distribution of Pseudo-nitzschia.