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

Abstract

Orinoco River influence in the Caribbean Sea, characterized by high nutrient input, causes a decrease of Trichodesmium populations. The Caribbean Time Series (CaTS) station, south of Puerto Rico (17°36'N 67°00'W), was mon­itored for 25 months in order to observe the Trichodesmium abundance pattern and the presence of the river plume. In gen­eral, mean Trichodesmium abundance was higher at the surface and decreased with depth; The mean upper Waler column (surface to 20 m) abundance was 54.1t32.6 col/m3. Within the sampling period, abundance was highly variable (1-700 col/m3). Correlation between Trichodesmium abundance and wind speed (p=0.002), chlorophyll a concentration (p=0.001), nitrate (p=0.02) and silicate (p=0. 003)concentrations were statistically significant. However, Trichodesmium abundance was not correlated with salinity (p=0.70), temperature (p=0.16) and seawater density (p=0.71) variatious at CaTS. Eastern Caribbean regions highly influenced by the Orinoco River discharge were devoid of Trichodesmium colonies.