Population Dynamics and Diversity of Synechococcus on the New England Shelf

Kristen Hunter-Cevera, PhD., 2014
Heidi Sosik and Michael Neubert, Co-advisors

To understand population changes of Synechococcus, hourly measurements of abundance at the Martha's Vineyard Coastal Observatory have been obtained with an automated flow cytometer since 2003. To ascribe changes in cell abundances to either growth processes, estimates of division rate are needed at the same resolution. A matrix population model that represents diel changes in cell size distributions is able to accurately estimate daily division rate for both cultured and natural Synechococcus. Application of the model to the 11-year time series of cell size distributions reveals that division rate is temperature limited during winter and spring, but light limited during fall. Calculated loss rates closely follow division rate in magnitude throughout the year. Large seasonal abundance patterns result from small, but systematic, offsets from zero net growth rate. Diversity within marine Synechococcus may affect population dynamics, and clade composition was assessed over annual cycles with culture-independent and dependent approaches and high through-put sequencing of a diversity marker provided quantitative assessment. Five main Synechococcus oligotypes showed seasonal abundance patterns and suggest that features of seasonal abundance are affected by the underlying diversity structure. Synechococcus abundance patterns result from a complex interplay among seasonal environmental changes, diversity, and biological losses.