ABSTRACT
The intertidal fauna of three Mediterranean beaches and nine Red Sea beaches along the coasts of Israel and Sinai were examined during the summer of 1979. Marine invertebrate infaunal community structure was studied in terms of species composition, density, diversity (H') and evenness (J'). The eastern Mediterranean intertidal sand beaches were depauperate in numbers of species and low in density; only 7 species were collected and intertidal density averaged 153/m2. No Lessepsian migrants were found. The Red Sea sandy beaches were rich in species (149 species collected) and had the highest diversity indices (H') reported worldwide for intertidal sand beach communities. Contributing factors to this high diversity include greater environmental stability, greater specialization among species and the large species pool of the Indo-Pacific province. The average density of infaunal species in these beaches was 1347/m2. Density of Red Sea infaunal organisms showed a significant negative correlation with median particle size of substrate.