Biogeographical homogeneity in the eastern Mediterranean Sea. II. temporal variation in lebanese bivalve biota

Lebanon (eastern Mediterranean Sea) is an area of particular biogeographic signifi-cance for studying the structure of eastern Mediterranean marine biodiversity and its recent changes. Based on literature records and original samples, we review here the knowledge of the Lebanese marine bivalve biota, tracing its changes during the last 170 yr. The updated checklist of bivalves of Lebanon yielded a total of 114 species (96 native and 18 alien taxa), accounting for ca. 26.5% of the known Mediterranean Bivalvia and thus representing a particularly poor fauna. Analysis of the 21 taxa historically described on Lebanese material only yielded 2 available names. Records of 24 species are new for the Lebanese fauna, and Lioberus ligneus is also a new record for the Mediterranean Sea. Comparisons between molluscan records by past (before 1950) and modern (after 1950) authors revealed temporal variations and qualitative modifications of the Lebanese bivalve fauna, mostly affected by the introduction of Erythraean species. The rate of recording of new alien species (evaluated in decades) revealed later first local arrivals (after 1900) than those observed for other eastern Mediterranean shores, while the peak in records in conjunc-tion with our samplings (1991 to 2010) emphasizes the need for increased field work to monitor their arrival and establishment. Finally, the scarce presence (or total absence) in the most recent samples of some once common habitat-forming species, as well as of some other native taxa, con-firmed their recent rarefaction (or local extinction), possibly related to their replacement by the aliens Brachidontes pharaonis, Spondylus spinosus and Chama pacifica. © Inter-Research 2013.