Cyanoprokaryote assemblages in eight productive tropical Brazilian waters

Cyanoprokaryote assemblages of eight very productive Brazilian lakes are described and the main driving forces of their dominance are considered. Relative abundance of blue-greens is shown to have been positively related to temperature, but not to pH or total-P and to have been negatively associated with light, mixing, NO3, but not with NH4, total N or total N/total P ratio. Both heterocytic and non-heterocytic groups were negatively related to NO3. However, if Cylindrospermopsis species are considered as non-N2-fixing organisms (only 10% of the filaments carried heterocytes), the lakes could be considered as dominated by non-N2-fixing populations during most of the years. In this new scenario, non-N2-fixing were dominant in NO3 (but not NH4) deficient lakes, and in both NO3 and NH4 deficient conditions. Assemblages S, Sn, H, M, X1, as groups of descriptor species of systems having similar features as proposed by Reynolds (1997: Ecology Institute, Oldenburg), were representative of warm, shallow, turbid, enriched and frequently mixed lakes. We propose to move some species from Z (picoplancton of oligotrophic lakes) to X1 assemblage (nanoplankton of eutrophic lakes) and we comment on Microcystis species of M assemblage from mixed shallow lakes in relation to Lm assemblage of end-summer in temperate lakes. S and Sn assemblages, which comprise species which are good-light antennae, were the best represented group in these generally turbid and shallow lakes.