Variação espacial e temporal da comunidade fitoplanctônica em uma seção do Reservatório de Passo Real, RS, Brasil

Abstract

Phytoplankton is a community of microscopic organisms, of great ecological importance and adapted to several environmental modifications. Ceratium furcoides is a dinoflagellate of the genus Ceratium found in marine habitats but in recent years is being considered an invading organism in freshwater environments both in North and South America. This work aims to describe a profile of the phytoplankton community and the occurrence of C. furcoides in an annual cycle in the water column at Passo Real Reservoir, Quinze de Novembro, RS. Phytoplankton samples were collected from one sampling station in the reservoir (-28.744702°S, -53.139704°W) in the four seasons (Winter, Spring, Summer and Autumn) and four times each day:at 9:00 a.m., 1:00 p.m., 4:00 p.m. and 6:00 p.m in four depths of the water column (sub-surface, depth of disappearance of the Secchi disk (d. secchi), limit of the euphotic zone and depth of 8 meters). A five litre Van Dorn bottle was used for water collection. Samples were concentrated in situ using a 25 μm mesh plankton net in amber flasks and preserved with 1% Lugol solution. The abiotic variables were measured in situ and in the laboratory with the aid of portable devices. The taxonomic identification of phytoplankton was performed using specialized bibliography. Phytoplankton quantification was performed in an inverted microscope. Migration of the phytoplankton community in the water column was observed during the study period. Cell density differed between depths, time of day and seasons. High temperatures in the water column were found as key factors causing intense blooms of the dinoflagellate C. furcoides.