This research documented the optical properties of the photosynthetic pigments, time series abundance, and remote sensing reflectance of Trichodesmium populations in the upper water column at the Caribbean Time Series Station (CaTS), south of Puerto Rico, and the eastern Caribbean Sea.

The Caribbean regions highly influenced by the Orinoco River discharge were devoid of Trichodesmium colonies. Correlations between Trichodesmium abundance and wind speed, Chl a concentration, nitrate and silicate concentrations were statistically significant (p<0.05). However, Trichodesmium abundance was not correlated with salinity, temperature and sigma-t variations in CaTS.

Temporal and spatial relative proportions of the main photosynthetic pigments (chlorophyll a and phycoerythrin) in Trichodesmium colonies were highly variable. Colony pigment content generally increased as water column depth increased. Absorption and fluorescence excitation maxima of Trichodesmium phycoerythrin were similar. The in vitro fluorescence emission maximum was 10 nm greater than in vivo emission. Trichodesmium colony phycoerythrin content was 2.5 times greater than chlorophyll a content. The PUB/PEB chromophore ratio was always greater than 1 and varied between 1.4 and 4.6.

Reflectance spectra and the derivative analyses of natural and artificial Trichodesmium bloom conditions were similar and showed five optical signals at: 436-439 nm and 676 nm (chlorophyll a), 492-498 nm (PUB chromophore), 542-547 nm (PEB chromophore), 567-570 nm (phycoerythrin natural fluorescence), and 623-630 nm (phycocyanin). Relative reflectance was inversely related to Trichodesmium abundance. The PUB chromophore signal was greater than the PEB chromophore and chlorophyll a signals. Spectroradiometric data and derivative analyses were useful techniques to study Trichodesmium abundance in CaTS. An algorithm to estimate Trichodesmium abundance using the fourth derivative value (498 nm and 550 nm) of the reflectance spectra was developed.