Diversity of juvenile fish assemblages in the pelagic waters of Lebanon (eastern Mediterranean)

The opening of the Suez Canal resulted in the introduction of Indo-Pacific organisms (Lessepsian) to the eastern Mediterranean. Available information on the Levantine ichthyofauna concerns mainly necto-benthic species, while pelagic ones remain mostly uncharacterized. This paper presents a preliminary assessment of biodiversity and its temporal changes on the Lebanese coast (eastern Mediterranean) using species composition and abundance of pelagic communities as indicators. For this purpose, a total of 11,192 fishes, representing 32 species and 19 families were collected with purse seines. Lessepsian species represented 40.9% of the species number in the purse-seine catches but only 0.48% in abundance of individuals and 1.57% in biomass. The families most represented in terms of abundance were the Clupeidae (49.28%), the Engraulidae (41.69%) and the Scombridae (7.01%); in terms of biomass these families represented 56.76, 22.04 and 9.72%, respectively. Abundance and biomass exhibited clear temporal fluctuations with Sardina pilchardus and Scomber japonicus dominating the catches between May and June, and then replaced by Sardinella aurita in July and Engraulis encrasicolus in August. The highest values of species richness (12 species) and diversity indices (H′ = 1.37; D = 0.71) were recorded in the last two weeks of June while the lowest values (5 species, H′ = 0.26; D = 0.11) were recorded in early August. While Lessepsian fishes represented a minor part in terms of landings, they contributed considerably to the diversity of pelagic fish assemblages in Lebanese waters.