MEPS 300:21-37 (2005)  -  doi:10.3354/meps300021

ABSTRACT: The temporal dynamics of heterotrophic bacteria and Synechococcus-type cyanobacteria communities were studied in a coastal habitat characterised by strong hydrodynamic variability using 10 s (microscale) and 30 min (small-scale) sampling intervals. Flow cytometric analysis allowed for the discrimination of 3 populations of heterotrophic bacteria and the examination of the Synechococcus cell cycle. During the 11 h small-scale study, 2-fold changes in the total abundance of both the bacterial and Synechococcus communities were observed, and clear temporal patterns in the abundance, activity and cellular state of the 2 populations were evident. Cumulative sum analysis further revealed distinct periods and trends in the temporal dynamics of the bacterial and Synechococcus communities. Shifts in the abundance of all heterotrophic bacterial populations were significantly correlated to turbulent energy dissipation. No such correlation was evident for the Synechococcus population, which instead appeared to follow a diel cell cycle very similar in nature to patterns observed in other environments. In 2 microscale studies, conducted during dissimilar hydrodynamic conditions, approx. 2-fold shifts in the abundance of the bacterial and Synechococcus populations were also observed. Microscale temporal patterns were dominated by localised variability and the existence of hotspots in abundance and activity, although cumulative sum analysis also revealed more general trends, sometimes occurring over periods of several minutes. Fundamentally different patterns, in the extent of temporal variability and coupling between the different microbial populations, were observed between the microscale and small-scale studies, suggesting that intrinsically different mechanisms and responses occurred independently and simultaneously at the different temporal scales. Furthermore, the variability in microbial parameters observed over these short temporal scales indicates the profound importance of microscale and small-scale processes in the ecology of communities of marine microorganisms.

KEY WORDS: Heterotrophic bacteria · Synechococcus · Small scale · Microscale · Temporal variability