Phytoplankton pigments from Coastal Mississippi waters were measured to determine the spatial and temporal distributions and composition of phytoplankton communities. Concentration of phytoplankton pigments were analyzed using High Performance Liquid Chromatography (HPLC) and the compositional changes in phytoplankton communities were determined with CHEMTAX 1.95. Surface water was collected for two years (September 2007-November 2009) at three sampling sites on a monthly basis. The stations were located at the Bay of St. Louis (station 1), the Mississippi Sound (station 4) and the Mississippi Bight (station 8), following a salinity gradient. A time series of the observations documented the variability of different taxonomic groups and phytoplankton abundance in Mississippi waters. Phytoplankton abundance and species group composition were related to environmental variables. Phytoplankton abundance did vary within stations and seasons being greater in coastal waters during the summer months. Diatoms were the major group at stations 1 and 4 where there was no major seasonal trend. At station 8 there was a clear seasonal trend where diatoms predominated in the winter, prymnesiophytes increased in spring, and cyanobacteria and diatoms predominated during the summer
