Significance of bacterial activity for the distribution and dynamics of transparent exopolymer particles in the Mediterranean sea.

The study of transparent exopolymer particles (TEP) in the Mediterranean Sea is particularly relevant as they can be promoters of mucilage events, a frequent phenomenon there. We assessed the influence of bacterioplankton on TEP distribution and dynamics across the west-east axis of the Mediterranean Sea. We performed an extensive study of TEP, dissolved carbohydrates, and their relationships with bacterial abundance and bacterial production (BP). A significant and positive relationship was observed between BP and TEP in the study region (r (2) = 0.51, p < 0.001). The direct release of TEP by bacteria was experimentally corroborated using regrowth cultures where increases in TEP tracked bacterial growth in abundance and production. These TEP increases were positively related to the increases in BP (r (2) = 0.78, p < 0.05). The consistency (similar slopes) of the regression lines between BP and TEP in natural conditions and between the increases of BP and TEP in the experiments underlines the relevant role of bacteria in the formation of TEP in this area.