Phytoplankton of the Middle Paraná River during an anomalous hydrological period: a morphological and functional approach

DEVERCELLI, M.

HYDROBIOLOGIA

Springer-Verlag

Lugar: Berlín; Año: 2006 vol. 563 p. 465 - 478

0018-8158

Abstract The Paraná River mainstem was sampled monthly (November 1999-December 2000) in order to analyse phytoplankton structure and dynamics during a period of extreme low water discharge. Physiognomic groups, size fractions, taxonomic groups, species and Reynolds et al. (2002) functional groups were studied in relation to environmental variables. The phytoplankton comprised an unusual development of small unicellular flagellates (1-20 mm), whereas large size algae such as the commonly recorded Aulacoseira were present with very low abundances. Groups Y (Cryptomonas spp.), X2 (Chlamydomonas spp., Rhodomonas minuta followed by a silicean chrysophyte) and D (Skeletonema cf. subsalsum and small centrics in minor proportion) dominated the phytoplankton community. Groups X2 and Y dominated at drought phase (November-December 1999). During the coupling of increasing waters and high suspended solids (February-May 2000) minimum abundance was exhibited. The highest densities were registered during mid-waters (Y, D, X2) when a constant river-floodplain feedback occurred (September-December). The connectivity between the main channel and its alluvial valley, and their interaction resulting from the regular alternation of hydrological fluctuations, play a steering role in structuring the potamoplankton of large rivers. The multivariate RDA showed that water discharge and transparency highly explained a significant proportion of the functional groups variation. The functional classification is proposed as a useful approach in reconstructing the phytoplankton community. The differences in structure from the typically described potamoplankton for the Paraná were maintained throughout the study period. The perseverance of the community changes that occurred during the drought depends, in part, on the persistence and magnitude of this anomalous phase.