Tide-induced Changes in the Phytoplankton Communities of three Amazon Estuaries (Para - Northern Brazil)

Sodre, D. K. L., Matos, J. B., Costa, K. G. da, Pereira, L. C. C. and Costa, R. M. da, 2011. Tide-induced Changes in the Phytoplankton Communities of three Amazon Estuaries (Para Northern Brazil). Journal of Coastal Research, SI 64 (Proceedings of the 11th International Coastal Symposium), 1574 - 1578. Szczecin, Poland, ISSN 0749-0208 The present study focused on the composition and density of phytoplankton in three Amazon estuaries, and on the effects of hydrological variables on community dynamics. Subsurface water samples were collected at three stations in October (spring tide) and November, 2007 (neap tide). Water temperature, salinity, pH, dissolved oxygen and chlorophyll a concentrations were also measured. Samples for qualitative analyses were obtained by horizontal hauls using a 64 pm-mesh plankton net. Additional water samples were collected for quantitative analyses. Plankton density was measured by Utermohl's method, and the data were analyzed using a one-way ANOVA and cluster analysis. Mean salinity ranged from 0 to 11.0 psu, water temperature from 27.9 to 28.8 degrees C, dissolved oxygen from 4.9 to 6.2 mg.L-1, and pH from 6.7 to 7.7. Seventy-three microphytoplankton taxa were identified, with a predominance of diatoms at all three sites. Phytoflagellates were the most abundant group. Biomass ranged from 5.10 mg.m(-3) to 25.74 mg.m(-3). Diversity varied from 0.73 to 2.84 bits.cell(-1), while evenness ranged from 0.20 to 0.61. Cluster analysis revealed the formation of two groups. The results indicate that the proximity to marine waters and consequent fluctuations in salinity levels were the primary determinant of the spatial distribution of phytoplankton at the three sites. Tide levels also had an effect, with the highest densities and biomass being recorded during neap tides, when the water was less turbulent, and the greatest diversity being observed during spring tides, when the inflow of water - and new species - from adjacent areas was most accentuated.