Diversity,habitats and size-frequency distribution of the gastropod genus Conus at Dahab in the Gulf of Aqaba,Northern Red Sea

Topographically complex subtidal reefs of the Indo-West Pacific region are characterised by a high species richness of cone snails of the genus Conus (up to 36 on some reefs) but low population densities (≤1 individual/m²), whereas Conus assemblages on reef flats usually support fewer species (5–9) and high population densities (up to 5.2 individuals/m²). Subtidal sand areas are known to be least species-rich (1–6 species). Although the diversity of this predatory gastropod genus has been described previously from different areas of the Indo-Pacific, little ecological information is available on Conus in the Northern Red Sea. Therefore, data from five habitat types were obtained along 73 line-transects (245?m²⁾, which yielded ecological data for a total of 175 individuals of 9 species. In accordance with former findings, our results demonstrate that the reef flat was the habitat with the highest observed population densities (6.15 individuals/m²) but low species diversity (H’ = 0.9; 5 species); subtidal reefs, in contrast, were characterised by low densities (0.13 individuals/m²) and a relatively high species diversity (H ‘= 1.5; 6 species). This suggests that Conus diversity and species richness in the Northern Red Sea around Dahab is lower than in other parts of the Indo-West Pacific region. Furthermore, hardand soft substrata were dominated by different Conus species in accordance to the distribution of favourable microhabitat patches, the degree of physical stress and the availability of refuges and prey organisms. The fact that these Conus were predominantly small-bodied vermivores (size range: 6–85?mm; mean shell size: 15?mm; SD = 9?mm) suggests that this size class possesses an advantage over molluscivores and piscivores. Except for subtidal reefs, which showed a highly variable species composition, the studied habitat types around Dahab were characterised by distinct assemblages of Conus.