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Contribution à l’étude des microalgues épiphytes dans les eaux côtières du golfe de Tunis : Cas des espèces du genre Ostreopsis Schmidt, J. (1901).

Abstract : The Gulf of Tunis, under high anthropogenic pressure, is a favorable terrain for harmful benthic dinoflagellate blooms (BHABs). Seasonal monitoring of the spatial and temporal distribution of epiphytic and planktonic microalgae coupled with environmental factors was studied for one year from october 2013 to october 2014 at 6 stations in the Gulf of Tunis. Harmful microalgae assemblages were dominated by three toxic epiphytic dinoflagellates: Ostreopsis sp., Prorocentrum lima and Coolia monotis. They were observed both in macrophytes and in the water column. The proliferation of Ostreopsis sp. is widespread in summer and blooms of P. lima and C. monotis were mainly recorded in spring. The morphometric analysis of Ostreopsis cells revealed a large variability in cell size at the different sampling stations of the Gulf. The dorso-ventral to antero-posterior diameter (DV/AP) ratio also varies from station to another. A weekly monitoring of the spatial and temporal distribution of Ostreopsis cf. ovata epiphytic and planktonic coupled with environmental factors was studied during 2015 and 2016 summer seasons at 5 stations in the Gulf of Tunis. The blooms were mainly detected between July and August. The concentrations of Ostreopsis cf. ovata measured are the highest ever recorded on the Tunisian coasts (9,91 × 105 cell. g-1 MF on macroalgae ; 5,11 × 105 cell. dm-3 in the water column). Ostreopsis cf. ovata peaks were observed when salinity and water temperature reached their high values, and when nitrites, nitrates, total nitrogen and silicates concentrations were low. Spatial variation is observed along the Gulf coast, suggesting that some sampling stations appear more favorable to the development of Ostreopsis cf. ovata than others. The alternative counting approaches MOL and OPR of Ostreopsis cf. ovata, implemented during the M3-HABs project and tested in this study, are in good agreement with the manual counting results. A predictive model of Quantile Random Forests type was used and could describe the abundance of Ostreopsis cf. ovata in the water column and macrophytes in response to 10 meteorological variables used within this model.
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Mohamed Amine Hachani. Contribution à l’étude des microalgues épiphytes dans les eaux côtières du golfe de Tunis : Cas des espèces du genre Ostreopsis Schmidt, J. (1901).. Ecologie, Environnement. Université Bourgogne Franche-Comté; Université de Tunis El-Manar. Faculté des Sciences de Tunis (Tunisie), 2019. Français. ⟨NNT : 2019UBFCD042⟩. ⟨tel-02548513⟩

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