Variability in the Structure of Planktonic Microalgae Assemblages in Water Column Associated with Posidonia oceanica (L.)‎ Bed in Tunisia

الملخص EN

Patterns of phytoplankton in areas with seagrass (Posidonia oceanica) and areas without seagrass were quantified in the coast of Chebba (East of Tunisia).

Replicate samples were collected at August 2011, from four stations (separated by 500 of metres).

The diversity of phytoplankton was high around P.

oceanica meadows compared to area without seagrass.

A possible explanation to this finding is that water motion and hydrodynamics forces cause leaves agitation allowing the passage of epiphytic species in the water column.

Our results also show an increase of abundance of potentially toxic dinoflagellates around Posidonia bed such as Alexandrium minitum, Amphidinium carterae, Karenia selliformis, Coolia monatis, Karlodinium veneficum, Ostreopsis ovata, Prorocentrum concavum, P.

minimum, P.

rathymum, and P.

lima.

Installation of fish farms on Posidonia beds should be avoided, not only to preserve this vulnerable habitat, but also to avoid fish contamination by toxic species derived from the resuspension of epiphytic community on seagrass substrata to the water column.