Factors affecting the distribution of two Synechococcus ecotypes in the coastal Adriatic Sea

Abstract

        Distribution and abundance of two Synechococcus ecotypes, phycocyanin-rich cells (PC-SYN) and phycoerythrin-rich cells (PE-SYN) were studied in the surface layer of the central Adriatic Sea during the 2015-2016 period. The studied area included several estuarine areas, and coastal to open sea trophic gradients, covering a wide range of seawater temperatures (11.82 - 20.75^oC), salinity (4.47 - 38.84) and nutrient concentration. The abundance of PC-SYN ranged from 0 to 79.79 x 10³ cell mL^-1 and that of PE-SYN from 5.01 x 10³ to 76.74 x 10³ cell mL^-1. Both ecotypes coexisted in the studied waters with PC-SYN cells dominating during spring and PE-SYN during winter and autumn. PC-SYN showed a significant positive relationship with temperature and strong positive responses to nitrogen nutrients, whereas PE-SYN positively responded to phosphate availability. The relative ratio of phosphorus availability and total inorganic nitrogen nutrients (N/P ratio) affects the spatial distribution of the two Synechococcus ecotypes.