A comparison of the density and diversity of intertidal benthic molluscs at a sheltered and an exposed tropical coast around Mauritius Island

Abstract

This study compared spatial variations in the density and diversity of marine benthic molluscs along Belle Mare and Gris Gris, a sheltered and an exposed intertidal zone, respectively, in Mauritius. Species density was assessed using the random quadrat method (1 m x 1 m). Grain size distribution was measured by sieve analysis. Shannon-Wiener (H’), evenness (E) and Simpson’s (D) indices were used to assess diversity. Coarser sediment was found at Gris Gris indicating the prevalence of relatively harsher wave conditions as compared to Belle Mare. Sixteen mollusc species were identi ed at Belle Mare (12 on rocky and 4 on sandy substrata) and seven species at Gris Gris (6 species on rocky and 1 on sandy substrata), with the families Planaxidae, Cerithiidae and Neritidae being common to both sites. Shannon-Wiener and evenness indices were higher at Gris Gris. Simpson’s index indicated higher dominance at Belle Mare, evident from the high density of Planaxis sulcatus (514.42 ± 221.63 individuals m-2) (mean ± SE). Turbo setosus was found in highest density (1.20 ± 0.20 individuals m-2) at Gris Gris. Though Belle Mare has higher intertidal mollusc abundance, the diversity was lower due to high dominance of species. This observation possibly signi es suitable physical conditions for species growth and survival at Belle Mare.