Phytoplankton from the Southern Coastal Fringe of the Rio-de- La-Plata (Buenos-Aires, Argentina)

GOMEZ, N.; BAUER, D. E.

HYDROBIOLOGIA

Kluwer

Año: 1998 vol. 380 p. 1 - 8

0018-8158

Abstract Structural characteristics of spring phytoplankton from the Southern Coastal Fringe of the Río de la Plata between 58°320 and 57°410 W, up to 10 km from the coast line are analysed. From 126 recorded taxa, 69 had a relative frequency above 5%. Main frequencies coincided with main quantitative abundances, corresponding to centric diatoms of the genus Aulacoseira – A. granulata var. augustissima especially – Stephanodiscus hantzschii and the coccal green Dictyosphaerium pulchellum and D. subsolitarium; the exception was the Cyanophyceae Microcystis aeruginosa, which showed the greatest quantitative abundance, but was not among the most frequent species. Centric diatoms accounted for most of the biovolume. Average phytoplankton density was 259 cells ml-1 (11–3700 cells ml-1). Diversity index (H0) varied from 0.51 to 2.78 bits ind-1. Phytoplankton size structure was: 43% picoplankton, 56% nanoplankton and 1% microplankton. Quantitative data on selected species were assessed for similarity among stations, 74% are joined in a group dominated by Aulacoseira sp. pl. and codominated by coccal green algae. The groups dominated by Stephanodiscus hantzschii and Microcystis aeruginosa included stations affected by pollution. Algal patchiness was greatest following low tide river currents. The assessed phytoplankton was eutrophic, oligohalophilous and mesosaprobic, a composition in agreement with some characteristics of a true potamoplankton.