Abstract

Objective: To compare the composition of the phytoplankton classes during the two spring studies, to study whether the spatial distribution of the phytoplankton is stable or not between spring 2010 and spring 2011 and to estimate the abiotic factor that mostly affects the structure and the richness of phytoplankton. Methods: Phytoplankton sub-samples were counted under an inverted microscope using the Utermöhl method. Phytoplankton identification was made from morphological criteria after consulting various keys. Results: Results showed a significant difference from spring 2010 to spring 2011 regarding nitrate/phosphate ratio, with high value in spring 2010 (30.19 ± 25.70). Relatively low nitrate/phosphate ratio (1.13 ± 0.53) during spring 2011 might result from phosphogypsum. Phytoplankton was characterised by the proliferation of Bacillariophyceae (46%–78% of the total microphytoplankton) and by the large number of Euglenophyceae. Thirty two Bacillariophyceae species were identified at every station, represented essentially by Amphora sp., Navicula sp., Coscinodiscus sp. and Grammatophora sp. The results advise that Bacillariophyceae are usually adapted to particular ecological environment. Conclusions: This study shows that hydrological conditions in the south coast of Sfax present a high spatial and seasonal variability. The phytoplankton community distribution showed clear variations along the coastal stations during a spring cruises conducted in May 2010 and May 2011. The phytoplankton community found along the coast was dominated by opportunistic Bacillariophyceae species.

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