The structure of the phytoplankton community of Princesa beach (Maiandeua island) was investigated during a nyctemeral cycle in the months of November/08, March/09, June/09 and September/09 to verify the effects of certain environmental variables on this community. The microphytoplankton of Princesa beach was represented by 98 taxa with the dominance of the diatoms, which were followed by the dinoflagellates and cyanophytes. The qualitative study revealed that Coscinodiscus perforatus Ehrenberg was abundant in March (45.6%) and June (45.1%), whereas in the quantitative analysis Dimeregramma minor (Gregory) Ralfs was dominant, mainly in November/08 (82.0%) and September/09 (83.0%). Biomass (chlorophyll-a content) was significantly higher in March/08 (U= 0.0; p <0.05). The average total phytoplankton density was significantly higher during the rainy period (F= 6.2; p< 0.05), mainly in June (1,223 ±110 x 10³ cell L-1). K-dominance curves showed a gradual decrease in diversity along the dry period. Non-Metric Multidimensional Scaling analysis (MDS) revealed the formation of three groups, whereas Principal Component Analysis (PCA) showed that salinity and turbidity were the main variables that defined the components. Princesa beach is a dynamic environment where ressuspension processes promote the shift between phytoplankton and phytobenthos populations. High rainfall and the increase in river runoff were responsible for an increase in nutrient availability contributing to the development of phytoplankton, mainly during the rainy period.
Plankton; Environmental variables; Amazon littoral
