BIODIVERSITY ASSESSMENT OF TERRESTRIAL SNAILS (MOLLUSCA, GASTROPODA) OF ESSAOUIRA' DUNES OF MOROCCO: TESTING FACTORS AFFECTING THE DISTRIBUTION OF TERRESTRIAL MOLLUSCS

Essaouira dunes of Morocco is a Biological and Ecological Interest Site (BEIS) that is recently impacted and threatened by human activities and climate change. Hence, this dune ecosystem needs thorough attention to preserve its biodiversity. Our study was carried out to assess the terrestrial mollusc diversity of this BEIS, and to figure out the relationship between environmental factors and terrestrial gastropods distribution. Six stations were chosen according to the variation of ecological factors, such as: type of soil, presence of limestone rocks, type of vegetation, and wind speed. The sampling was adopted using both visual search and quadrat approach. The results revealed the existence of 23 species of terrestrial molluscs; belonging to 18 genera and 11 families. Geomitridea and Helicidae are the most dominant families (56.52%). The highest specific richness was recorded in Ounagha' station, with 17 species. The malacofaunal diversity between stations was also determined by: Constancy, Shannon, Equitability, Simpson and Jaccard indices. The relationship between the distribution of terrestrial snails and abiotic factors were involved using Canonical Correspondence Analysis (CCA). The results showed that wind speed and type of soil represent those relevant factors affecting the distribution patterns of terrestrial gastropods.