The abundance of Synechococcus in the East China Sea (ECS) was tracked during two sets of cruises in 1997 - 1998 and 2004. These data were combined with information from the literature to examine the hypothesis wherein variations in Synechococcus abundance were linked to the magnitude of seasonal temperature ranges. An index of the amplitude of Synechococcus seasonal abundance relative to their minimum abundance (ΔN/N_min) was well correlated with the range of sea surface temperature (ΔT). These results suggest that the regional range of temperature is a relatively good predictor for the relative seasonal change in Synechococcus abundance within many environments.