The sinking capability of Phaeocystis based on DNA signals in short-term sediment traps. ANT-28-3

There is a controversy discussion about the contribution of the genus Phaeocystis to the vertical carbon export. There is evidence arguing for and against sedimentation of Phaeocystis. So far, the sinking capability was investigated only with methods depending on morphological features (microscopy) and fast degradable substances (biochemical analyzes). In this study, we determine the occurrence and abundance of Phaeocystis in short-term sediment traps and the overlying water column during a 12 day time period in the Atlantic sector of the Southern Ocean with 454-pyrosequencing and microscopy counting. In the sediment trap samples, we only found few sequences belonging to Phaeocystis, which was not reflecting the situation in the water column above. The cell counts showed the same results. We conclude that Phaeocystis cells are not generally transported downwards by active sinking or other sinking processes. Thus, it is likely that they are largely recycled in the upper layers.