Ecological studies in the Bay of Paranaguá: I. horizontal distribution and seasonal dynamics of the phytoplankton

Abstract

Five stations were sampled monthly in the Bay of Paranaguá during one year cycle (1983-1984) to measure basic environmental parameters, phytoplankton biomass and photosynthesis with the purpose of understanding the principal factors that regulate the phytoplankton growth and distribution throughout the year. Surface temperature varied from 17 to 30ºC. The yearly average values for salinity, dissolved oxygen and pH ranged from 9.38 to 32.00‰, 5.17 to 5.53 ml/l and 7.46 to 8.18, respectively. Average concentrations of total inorganic nitrogen, phosphate and silicate varied from 3.31 to 8.48, 0.38 to 0.97 and 27.68 to 98.36 µg-at/l, respectively, with increasing concentrations toward the inner bay. Chlorophyll-a at the surface varied between 2.86 and 13.99 mg/m³ with high concentrations in the inner bay associated with high nutrient contents and lower salinities. Low photosynthetic rates were measured at the surface, varying from 0.01 to 7.36 mgC/m³/h. Phytoflagellates and Skeletonema costatum dominated the phytoplankton population during the study period. The temporal fluctuations in the inner bay are associated with the rainfall regime. High amounts of precipitation increase the concentrations of nutrients and consequently improve the phytoplankton growth. This is however limited by nitrogen deficiency (as indicated by the low N to P ratios observed) and turbidity.