Dynamics of Aerobic Anoxygenic Phototrophs along the trophic gradient in the central Adriatic Sea

Abstract

Although Aerobic Anoxygenic Phototrophs (AAPs) are widespread in aquatic environments, relatively little is known about their dynamics in the Adriatic Sea. Therefore, we investigated their distribution along the trophic gradient from coast to the open sea over a year-round period, for the first time, as well as the factors that influenced the spatio-temporal distribution. AAP abundances varied between 0.26 × 104 at the open sea, and 23.45 × 104 cell mL−1 in the estuarine area, while their relative abundances ranged between 1.13% and 23.88% respectively. The biomass of AAPs ranged between 0.07 and 6.24 μg C L−1; thus, we observed a trend of decreasing abundances and biomass of the studied groups from more eutrophic coastal to the oligotrophic open sea area. AAP biomass exhibited the highest values during summer in the estuarine areas and the lowest during winter in the open sea. The main driving factors for the whole picoplankton community variance were transparency (Secchi disc), chlorophyll and salinity, whereas AAPs were grouped with heterotrophic bacteria, picoeukaryotes and heterotrophic nanoflagellates. Our data indicate that phosphorus limitation in the environment could be an important factor for the AAP growth.