Seasonal Succession Patterns of Phytoplankton in the Bahía Blanca Estuary (Argentina)

Abstract

The Bahía Blanca estuary is a shallow, well mixed and highly turbid ecosystem. The phytoplankton is dominated by diatoms with Thalassiosira the major genus in number of species and numerical abundance. A longterm investigation was conducted from 1978 to 1991 including measurements of phytoplankton composition and abundance and environmental factors. Principal Components Analysis (PCA), applied to two periods of four years (1978–1981 and 1988–1991) corroborated the pattern of seasonal distribution in Bahia Blanca estuary; a winter-early spring bloom as the most important event in the annual cycle. This bloom was initiated usually in late-June and extended through September. Seasonal patterns of nutrient concentrations showed a decline coinciding with the diatom bloom and peaks of high concentrations in late summer and autumn. According to the long term observations on phytoplankton and the PCA results, the most important phytoplankton taxa in Bahía Blanca estuary exhibited one of three types of seasonal patterns: very recurrent, winter-early spring blooming species, which included Thalassiosira curviseriata, T. anguste-lineata, T. pacifica, Chaetoceros spp., Skeletonema costatum; species present year-round, e. g. non-blooming species Thalassiosira hendeyi and Paralia sulcata; species with peaks of abundance in late-spring or summer, and presenting more seasonal and interannual variability including phytoflagellates, and the diatoms Cerataulina pelagica and Guinardia delicatula.