Distribution of the cyanophyte Trichodesmium (Oscillatoriaceae) in the eastern Caribbean Sea: influence of the Orinoco River

Orinoco River influence in the Caribbean Sea, characterized by high nutrien t input, muses a decrease of Trichodesmium populations. The Caribbean Time Series (CaTS) station, south of Puerto Rico (17 degrees 36'N 67 degrees 00' W), was monitored for 25 months in order to observe the Trichodesmium abund ance pattern and the presence of the river plume. In general, mean Trichode smium abundance was higher at the surface and decreased with depth. The mea n upper water column (surface to 20 m) abundance was 54.1+/-37.6 col/m (3). Within the sampling period, abundance was highly variable (1-700 col/m(3)) . Correlation between Trichodesmium abundance and wind speed (p=0.002), chl orophyll a concentration (p=0.001). nitrate (p=0.02) and silicate (p=0.003) concentrations were statistically significant. However. Trichodesmium abun dance was not correlated with salinity (p=0.70), temperature (p=0.16) and s eawater density (p=0.71) variations at CaTS. Eastern Caribbean regions high ly influenced by the Orinoco River discharge were devoid of Trichodesmium c olonies.