Growth dynamics of marine Synechococcus spp. in the Gulf of Alaska

Vertical distribution of Synechococcus spp. varied seasonally, with cells evenly distributed in the mixed layer at the beginning of June, but concentrated in and below the pycnocline (40-60 m) in September. Experiments on strains isolated from the Gulf of Alaska indicate a duration of division of 10.5 h. The instantaneous growth rate was maximum in June at the surface (0.7 d^-1), but much lower in September in the mixed layer (about 0.25 d^-1) and lowest below the pycnocline (about 0.16 d^-1). In June near the surface, the contribution of Synechococcus spp. to phytoplankton carbon and total primary production was 21% and 8%, respectively. The contribution was lower in September in the surface but increasing with depth reaching maximum values at and below the 1% light level (50-60 m depth) of 31 and 68%, respectively. -from Author