Time lags in algal growth: generality, causes and consequences

Lagged algal growth responses are argued to be general phenomena occurring, whenever algal growth is enhanced by some growth stimulus, in all aquatic environments supporting planktonic or epiphytic communities. Lag phenomena can be accounted for through a hierarchical conception of microalgal ecology, involving the partition of lagged responses into an 'intrinsic' component, due to biochemical reorganization needed for rapid cell division, and 'extrinsic' component, due to variability in algal growth and loss rates that result in a lag between enhanced cell division and population growth. The plausibility of such an 'extrinsic' lag component was confirmed by simulation modelling, which also revealed that lag duration should decrease exponentially with increasing growth rate, and increase linearly with increasing variability in growth rate. Lag phenomena in algal growth may be of paramount importance in structuring aquatic ecosystems, because it results in the temporal (and spatial, in systems with important advective components) uncoupling between growth stimuli and algal growth. Further, lag phenomena impinge directly upon the interpretation of field data relating algal growth to contemporary environmental conditions.