Cyanoprokaryote assemblages in eight productive tropical Brazilian waters

Cyanoprokaryote assemblages of eight very productive Brazilian lakes are de scribed and the main driving forces of their dominance are considered. Rela tive abundance of blue-greens is shown to have been positively related to t emperature, 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 rati o. Both heterocytic and non-heterocytic groups were negatively related to N O3. However, if Cylindrospermopsis species are considered as non-N-2-fixing organisms (only 10% of the filaments carried heterocytes), the lakes could be considered as dominated by non-N-2-fixing populations during most of th e years. In this new scenario, non-N-2-fixing were dominant in NO3 (but not NH4) deficient lakes and in both NO3 and NH4 deficient conditions. Assembl ages S, S-n, H, M, X-1, as groups of descriptor species of systems having s imilar features as proposed by Reynolds (1997: Ecology Institute, Oldenburg ), were representative of warm, shallow, turbid, enriched and frequently mi xed lakes. We propose to move some species from Z (picoplancton of oligotro phic lakes) to X-1 assemblage (nanoplankton of eutrophic lakes) and we comm ent on Microcystis species of M assemblage from mixed shallow lakes in rela tion to L-m assemblage of end-summer in temperate lakes. S and S-n assembla ges, which comprise species which are good-light antennae, were the best re presented group in these generally turbid and shallow lakes.