Desmídias (chlorophyta) de um lago de inundação de águas pretas na Amazônia central

Abstract

The Amazon has a great amount of aquatic environments, influenced by the floodpulse, in which high richness of aquatic organisms is observed, in special the Desmids, organisms that are present in phytoplankton, favored by the characteristics of the Amazonian black water, which is lightly acid with reduced pH values and electric conductivity. This work presents a taxonomic survey of planktonic desmids of the Cutiuaú lake in National Park of Jaú in some periods of the floodpulse of Jaú River between the years of 2002-2004, and also verified the influence of these periods in the species richness of desmids. 109 samples were collected in ten stations of the Cutiuaú lake with a 25μm mesh plankton net and fixed with Transeau solution. In the moment of the sampling, limnological parameters such as depth, temperature, electric conductivity and transparency of the water were measured. The environment was characterized by depth values among 2.4 to 11.5 meters. The temperature of the water in the stations ranged between 27- 31.7°C. The pH oscillated from 3.3 to 5.2. The electric conductivity ranged from 10.8 to 68.7μS.cm-1. The values of saturation of dissolved oxygen oscillated among 6.8 and 68.7%. The transparency of the water, measured with a Secchi disk, oscillated between 0.6-1.3 meters. 105 taxa of desmids were identified and described, being 73% idenfified in specific level and 27% in infraspecifc level. The Desmidiaceae family showed a great richness with 85 taxa registerd, followed by Closteriaceae family with 17 taxa and Gonatozygaceae Family with one taxa. The genus Staurastrum Meyen belonging to the family Desmidiaceae, presented the largest number of species with 19 species, followed by Staurodesmus Teiling with 13, Euastrum Ehrenberg and Micrasterias Agardh with ten taxa each. The water level fluctuations may influence the richness of desmids species. In the increasing water level, the largest number of taxa was registered (98 species). In the decreasing water level 51 taxa were identified, in the high water level, 39 species and 23 registered taxa in the low water level. Of the 105 species registered for this study, 26 are considered as first citations of ocurrence of the species for the state of Amazonas.