Spatial and Temporal Physical Patterns Shape Synechococcus Ecophysiology and Population Dynamics in a New England Salt Marsh Estuary

Synechococcus comprise a diverse group of globally ubiquitous cyanobacteria that thrive in freshwater to marine habitats, yet little is known about factors that influence their growth in estuaries. Here we characterize the abundance of 16 Synechococcus oligotypes over an annual cycle in Sippewissett Marsh, a tidal estuary in Cape Cod, Massachusetts. Two Synechococcus blooms dominated by different oligotypes were observed in the spring and fall that were linked to temperature preferences. Samples taken at 7 sites in the coastal ocean and along the main channel of the estuary show that estuarine populations are strongly influenced by the oceanic end member, while more spatially isolated sites removed from tidal influence had markedly different community composition and relative abundances. High frequency (weekly) sampling during the summer revealed the co-occurrence of certain oligotypes and mirrored patterns observed offshore in other studies. Sippewissett Marsh therefore harbors a diverse Synechococcus community that shares ecophysiological traits with coastal populations, but spatial separation from seawater influence permits divergent community characteristics to emerge. This study demonstrates how spatial and temporal variability in physical environmental factors together drive the abundance and diversity of Synechococcus in a tidal estuary.