Les efflorescences phytoplanctoniques dans le golfe de Gabes (Tunisie) au cours de dix ans de surveillance (1995-2005)

Abstract

The data of the National Phytoplankton Monitoring Program are examined in the Gulf of Gabes during the period 1995-2005. A particular interest is assigned to the blooms events. We particularly examine the spatial and temporal variations of the responsible species and the relationships with the variability of temperature, salinity and pH. The results show that the period from August to January, with peaks in September and January, seems to be favourable to algal blooms. The dinoflagellates are responsible of 89% of the recorded blooms with the species Karenia selliformis representing 64% of the occurrences. Blooms of K. selliformis, although relatively frequent in a specific zone, their concentrations do not show statistically significant variations among sampled zones. This leads to suggest that blooms of this species would be initiated in different zones in the Gulf of Gabes. K. selliformis fluctuates also independently of years and months, but it shows a specific requirement for salinity (higher than 42 g/l). This parameter can be used as a marker to predict the appearance of K. selliformis in the Gulf of Gabes. The others phytoplankton species do not have any specific requirements for the studied abiotic variables