Epi- and endobiont faunal communities on an Egyptian Mediterranean rocky shore: species composition and their competition for space

The exposed calcareous rocky area of the Abu Qir Headland, east of Alexandria, Egypt which range from coarse grains, through pebbles, cobbles, and boulders to rocky platforms, was significantly colonized by sclerobionts (epibionts and endobionts). The epibiont species diversity was comparatively higher than that of endobionts. Epibiont communities included bryozoans (the anascan-grade cheilostome Biflustra savartii), serpulid (Hydroides elegans, Spirobranchus cf. tetraceros, Vermiliopsis striaticeps and Protula or Apomatus) and spirorbid (Spirorbis) wormtubes, and balanoid barnacles (Amphibalanus amphitrite, Balanus trigonus, and Perforatus perforatus). The cheilostome bryozoan colonies, which developed extensive sheets, proliferated on the study rocky shore either encrusting the bioeroded basement directly, or encrusting other epilithic taxa, particularly balanoid barnacles and serpulid worms. Encrusters displayed a remarkable marginal competitive interaction (overgrowth and stand-off) for space on the study rocky shore. On the other hand, endobionts were not well represented on the studied rocky shore exposure. It was possible to identify three ichnotaxa: Gastrochaenolites, Maeandropolydora, and Finichnus. The findings documented represent a significant contribution to our knowledge of sclerobionts composition, sequence of their colonization and/or bioerosion, and their mutual relationships on the intertidal rocky shore of the Abu Qir Headland.