FORMATION AND SIGNIFICANCE OF TRANSPARENT EXOPOLYMERIC PARTICLES IN THE NORTHERN ADRIATIC SEA

We examined the abundance and bacterial colonization pattern of transparent exopolymeric particles (TEP) during 2 different ecological conditions along a trophic gradient in the northern Adriatic Sea. Generally, neither TEP density (ranging from 0 to 600 TEP ml(-1)) nor mean TEP area were found to be correlated with chlorophyll a concentrations, although a tendency was discernible of increasing TEP density and area towards more eutrophic conditions. TEP area ranged from 12 to 7500 mu m(2) with TEP-attached bacteria inversely correlated with TEP aera. In laboratory experiments using water amended with dissolved organic matter released by a Chaetoceros sp. batch culture, we examined the influence of bacteria and turbulence on the formation of TEP. In both biotic and abiotic treatments subjected to turbulence, TEP density and area reached maximum levels within 24 h and retained this level over a period of similar to 40 h. In the stagnant treatment, however, TEP area declined rapidly after reaching a peak similar to 24 h after starting the experiment. Based on our experments, we conclude that turbulence of the water column is more important than bacteria in the formation of TEP. In situ fluctuations in TEP abundance might reflect not only differences in phytoplankton growth stage but also different turbulent regimes.