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

Abstract

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.

Variability in the Structure of Phytoplankton Assemblages in relation to Human Disturbance in Southern Coast of Tunisia

“…SIMPER generates a ranking of the species responsible for the significant differences. These analyses used a matrix composed of Bray-Curtis similarity coefficient generated with Log( + 1)-transformed species abundance data [13].…”

“…Analysis of variance (ANOVA) was used to test the hypothesis that the abundance of each group of taxa differed between disturbed and control stations [13]. Factor station was fixed.…”

“…To mix the sample, the bottle was gently tilted back and forth 10 times before pouring [12]. A 50 mL subsample was poured into the settling chamber and left to settle for 24 h. subsamples were examined in an inverted microscope at medium (× 200) magnification by scanning the entire surface of the settling chamber to enumerate epiphytic microalgae [12,13]. The total number of microalgae individuals ( ) contained in 1 litre expressed as number of individuals per litre is obtained by the following conversion: = ( × 1000)/(V), with = the number of individuals counted and V = the volume of the sedimentation chamber (50 mL) [13].…”

A Comparison of Abundance and Diversity of Epiphytic Microalgal Assemblages on the Leaves of the SeagrassesPosidonia oceanica(L.) andCymodocea nodosa(Ucria) Asch in Eastern Tunisia

“…These results are particularly useful in this area with the recent establishment of several fish farms because epiphytic dinoflagellates are easily resuspended in the water column [8] and that abundance of phytoplankton in vegetated areas is higher than in the unvegetated station [16]. Moreover, Marr et al [60] concluded that the underestimation of toxic dinoflagellates associated with a toxic event may be due, in part, to the lack of sampling of the benthic and epiphytic communities.…”

“…Epiphytic microalgae include many toxic species [13][14][15][16]. Knowledge of the epiphytes and potentially toxic species of microalgae is necessary to assess the influence of those species on fisheries exploitation and human health.…”