Seasonal distribution of ultraphytoplankton and heterotrophic prokaryotes in relation to abiotic variables on the north coast of Sfax after restoration
Résumé
The Taparura project was set up to restore the north Sfax coast (Tunisia) by shutting down the northern
phosphate plant responsible for chronic pollution and uncontrolled phosphogypsum dumping. The restoration
effect on coastal ultraphytoplankton (<10 lm) and heterotrophic prokaryotes was investigated
using conventional flow cytometry over four successive seasons during 2009–2010. Cell concentrations
were generally higher than values reported for the open sea, both in the western and eastern Mediterranean
basins. One striking point was that chl a concentration on the north Sfax coast was unchanged after
restoration but was still one order of magnitude higher than in the Gulf of Gabès. Restoration of pH, following
the shutdown of the phosphate processing plants on the north coast, appeared to reach normal
levels for seawater during the study, whereas seawater acidification persisted on the south coast where
plants are still in operation. The largest ultraphytoplankton biomass was from an unknown cell group,
whose identity and role needs to be established.