AbstractSynechococcus are unicellular cyanobacteria susceptible to environmental fluctuations and can be used as bioindicators of eutrophication in marine ecosystems. We examined their distribution in two Moroccan lagoons, Marchica on the Mediterranean coast and Oualidia on the Atlantic, in the summers of 2014 and 2015 using 16S rRNA amplicon oligotyping. Synechococcus representatives recruited a higher number of reads from the 16S rRNA in Marchica in comparison to Oualidia. We identified 31 Synechococcus oligotypes that clustered into 10 clades with different distribution patterns. The Synechococcus community was mainly represented by oligotype 1 (clade III) in Marchica. Cooccurring clades IV and I had an important relative abundance in Marchica in the summer of 2014, which is unusual, as these clades are widespread in cold waters. Moreover, Clades VII and subcluster “5.3” formed a sizeable percentage of the Synechococcus community in Marchica. Notably, we found low Synechococcus sequence counts in the Atlantic Lagoon. These results showed that the relative abundance of Synechococcus reads is not constant over space and time and that rare members of the Synechococcus community did not follow a consistent pattern. Further studies are required to decipher Synechococcus dynamics and the impact of environmental parameters on their spatial and temporal distributions.