The present study highlights the essential importance of malacology for understanding and preserving marine ecosystems. Its objective is to identify the molluscs of hard substrates, particularly along the northern coast of Tunisia. Sampling conducted between February and March 2024 at the sites of Bizerte, La Goulette, Sidi Raies, and Tabarka resulted in the collection of a total of 614 live mollusc specimens, representing 15 species, (13 gastropods and 2 bivalves). The composition of the fauna shows that the most dominant species is a pulmonate gastropod of Indo-Pacific origin: the false limpet Siphonaria pectinata. Furthermore, we observed that species richness varies according to the sampling site, highlighting the importance of local environmental conditions. The strong presence of Siphonaria pectinata, accounting for 75% of the overall sampling, suggests its ability to establish itself in the marine habitats of the northern coast and the Gulf of Tunis as an exotic species.
For the sampling, we used a square frame covering a quadrat of 25x25 cm, which corresponds to an area of 0.0625 m². Five replicates of the quadrat were collected for each station. It was fixed on the rocks at a depth ranging from 0 to 0.5 m (Figure 1). We started by scraping off the molluscs and gathering them in a bag.The bags were pre-numbered and labeled with the site name and date. Our study indicated that Siphonaria pectinata is the most abundant species in the overall sampling and provided new information on its distribution to monitor its impact on the marine ecosystem, particularly on the indigenous fauna.
This strong presence reflects the great diversity of micro-habitats available in hard substrates. It suggests that Siphonaria pectinata, as an exotic species, has successfully established itself along the northern coast, the Gulf of Tunis, and continues to expand in Tunisia towards the Gulf of Hammamet. The question arises: "Could Siphonaria pectinata pose a real threat to native species?" To assess the potential threat of Siphonaria pectinata, several aspects must be considered: competition for resources, impact on biodiversity, adaptability of native species, and ecological changes. This exotic species could directly compete with local species for resources and habitats, leading to a decrease in biodiversity and a possible reduction in native species populations.