DIVERSITE DES INVERTEBRES MARINS ET LEURS DISTRIBUTIONS. Etude effectuée dans la zone Nord-Ouest de Madagascar.

The study was carried out in the Diana region, in the north and north-west of Madagascar. The main objective is to demonstrate the diversity of marine invertebrates and their distributions. To achieve this goal, the study set three specific objectives: to inventory the taxonomic groups (Sponges, Cnidarians, Tunicates, Molluscs), to analyze the spatial variation between the different study sites for all taxonomic groups as well as for their morphotypes, and to study the distribution of samples as a function of depth. Four sites were selected for sampling, comprising several stations divided into two depth categories (P2: 20 to 40 meters and P3: 40 to 60 meters). Sampling was conducted by scuba divers, using a manual, selective sampling method. The results of the study showed a high diversity of sponges and cnidarians (Shannon-Wiener index > 2.8), while that of tunicates and molluscs was lower (Shannon-Wiener index < 2.3). The rarefaction curves revealed that taxonomic richness was not yet sufficiently determined for each group at all four sites. Community dissimilarity analysis showed that the Ambavanibe (P2), Diego (P2 and P3), Mangoaka (P3) and Voltigeur (P2 and P3) sites had high taxon richness. The Ambavanibe (P3) and Mangoaka (P2) sites show high frequency and low taxon richness. The vertical distribution of sponges in both P2 and P3 was the most dominant, with a higher frequency at depths between 20 and 40m. The taxonomic richness of molluscs and tunicates shows a difference between the two depth classes.

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15/09/2023