EVALUATING PHYTOPLANKTON DYNAMICS IN THE NEWPORT RIVER ESTUARY (NORTH-CAROLINA, USA) BY HPLC-DERIVED PIGMENT PROFILES

The composition and dynamics of phytoplankton assemblages during the s pring bloom in a shallow, coastal-plain estuary were characterized by high-performance liquid chromatography (HPLC)-derived pigment profiles . From mid-February through the first week in June 1991, samples were collected twice weekly at 2 sites within the Newport River estuary, No rth Carolina, USA. Pigment profiles, reflecting phytoplankton assembla ges dominated by diatoms, dinoflagellates, prymnesiophytes, cryptophyt es, and chlorophytes, were compared to phytoplankton cell counts. Ther e were significant (p less than or equal to 0.0005, r(2) = 0.49 to 0.6 3) relationships between the taxon-specific pigment concentrations and the taxon-specific cell numbers. HPLC-determined chlorophyll (chl) a biomass corresponded with the sum of the taxon-specific chl a biomass (p less than or equal to 0.001, r(2) = 0.95). Each taxon-specific biom ass was calculated based on chl a:accessory pigment ratios determined by regression analyses. Chl a biomass was also measured fluorometrical ly and compared with the HPLC results. Fluorometric analysis underesti mated biomass when prymnesiophytes, cryptophytes, and chlorophytes dom inated the phytoplankton. Despite the inherent environmental variabili ty of the estuarine sampling location, HPLC-derived pigment profiles d id provide division-level phylogenetic assessment of large, short-term changes in the phytoplankton composition and detected assemblage resp onses to event-scale perturbation effects (e.g. precipitation, wind). These results demonstrate that even in highly variable environments HP LC-based pigment analysis is a valuable tool, providing complementary information to the traditional methodology of cell counting.