ABSTRACT: We used literature data on marine bacterial (sub)group abundances, as determined by fluorescence in situ hybridization, to test whether the ecological variability of the different subgroups was similar to that of the bacterial community as a whole. Patterns of 6 major groups are described (Alpha-, Beta-, Gammaproteobacteria and Bacteroidetes, as well as Rhodobacteraceae and SAR11) and related to environmental variables such as chlorophyll a (chl a) concentration, salinity, and temperature, distinguishing between coastal or open-ocean environments. Coastal ecosystems exhibited higher relative abundances (average % of DAPI counts) of Bacteroidetes (23%), Beta- (11%) and Gammaproteobacteria (10%), and Rhodobacteraceae (6%), while significantly higher contributions of Alphaproteobacteria and SAR11 (32%) were on average enumerated offshore. Multiple regression analyses showed significant explanatory power of chl a and temperature on total and SAR11 absolute abundances (expressed as cells ml^-1), and of chl a and salinity levels on absolute abundances of Betaproteobacteria and Rhodobacteraceae. Other analyses revealed increasing contribution of Gammaproteobacteria for increasing temperatures and high temperature avoidance for Betaproteobacteria. Significantly different log-log regression slopes were found between bacterial group absolute abundances and chl a concentration at a global scale, ranging from 0.13 ± 0.04 (SE) for SAR11 to 0.53 ± 0.08 for Betaproteobacteria. The different patterns observed for the different groups, in coastal and open-ocean environments, suggest different niche preferences by each group as well as a coherent response to environmental factors.