P.S.Z.N.: Marine Ecology, zyxwvut 18 (4): 361-378 (1997) zyxwv 0 1997 Blackwell Wissenschafts-Verlag, Berlin ISSN 0173-9565 Accepted: June 20, 1997 Molluscan Hard-Substrate Associations in the Northern Red Sea zy M. ZUSCHIN zyxwvu & W. E. PILLER Institut filr PalSiontologie, Universitat Wien, Geozentrum, Althanstrasse 14, A-1090 Vienna. Austria. With 3 figures and 3 tables Key words: Northern Bay of Safaga, reef flats, tidal flats, scleractinian carpets, zyx Sarcophyion carpets. Abstract. The mollusc associations of 29 hard-substrate localities in the Northern Bay of Safaga (Red Sea, Egypt) were studied. The hard substrates were classified into 7 types: reef flats, intertidal rock bottom, very shallow subtidal conglomerate, Porifes carpet, faviid carpet, platy scleractinian associ- ation, Sarcophyron carpet. Based on a cluster analysis the molluscs of these hard substrates can be classified into 5 groups: Group A is dominated by Dendropoma zyxw maxima, Chamoidea and Tridacna maxima, group B by Pedum spondyloideum, T. maxima and Coralliophila neriioidea, group C by Chamoidea and Ceriihium ruppelli, group D by Modiolus auriculaius, Chamoidea, Morula yranulara and Neriia albicilla and group E by Chamoidea and Pirar hebraea. The latter group contains only samples which are generally poor in molluscs. Group A molluscs are diagnostic for reef flats, group B for Purites and faviid carpets, group C for Sarcophyton carpets and group D for tidal/shallow subtidal rock substrates. The different hard substrates are therefore characterized by diagnostic mollusc associ- ations and some of them could also be identified in the fossil record. Problem Ecological and paleoecological studies in tropical-subtropical reefoidal environ- ments typically focus on corals and coral communities. Other than this invertebrate group, molluscs are also frequently found inhabiting a variety of ecological niches, and like corals, have considerable fossilization potential. In this context, however, only minor attention has been paid to this group and most Indo-Pacific studies focus mainly on gastropods (e.g., FRANK, 1969; HADFIELD, 1976; AUSTIN et zy af., 1980; TAYLOR & REID,1984; SCHUHMACHER, 1993) or cover the easily accessible intertidal areas (e.g., TAYLOR, 1971; AYAL & SAFRIEL, 1981). Studies dealing with bivalves are generally rare (for a detailed review see MORTON, 1983) or restricted to particular taxa (e.g., LEE & MORTON, 1985; ARNOUD & THOMASSIN, 1990) and to date only few studies have been published in which the total mollusc fauna of various hard substrates was treated (e.g., MASTALLER, 1978; SHEPPARD, 1984). Within the framework of an integrated project in the northern Red Sea, the study of corals represents one particular topic (KLEEMANN, 1992; RIEGL & PILLER, 1997). Several coral associations (including both hard and soft corals) were dis- U. S. Copyright Clearance Center Code Statement: 01 73-9565/97/1804-036l$14.00/0