The Eastern Mediterranean Sea: tropical invasions and niche opportunities in a “Godot Basin”

Abstract

Biogeographia vol. XXIV - 2003 (Printed October, 31st 2003) Marine biogeography of the Mediterranean Sea: patterns and dynamics of biodiversity The Eastern Mediterranean Sea: tropical invasions and niche opportunities in a “Godot Basin” l\/[ARCO OLlVERlO*, MARCO TAVlANl** *Dz'pzzrtimem‘0 di Bin/ogzkz Am'mri/e‘ e a'e[[’U0m0, Urziveisitiz “La Szzpienzzz ”. Vizzle zz’e[[’U1ziz1er5z’z‘z‘z 32, [—00185 Roma (Italy) c—7mzi[: mrzrm. 0/z'z/erz'0@zmz'r0nuz1. it **]S]l4/lR—]l/Izzrine Geology Diz/ision, CNR, z/izz Goeezfi 10], 140129 Bologmz (Italy) e—mzzz'l: mmro. tzzvizzizi @b0. irzmzr. cm. 7'2‘ Key words: Lessepsian, alien species, Levant basin biogeography, niche. SUMMARY The progressive colonization of large sectors of the Mediterranean Sea by tropical—subtropical alien species (Lesscpsian “migrantsq and introduced aliens) highlights a rematltable biogeographic paradox. The Eastern Mediterranean Sea, and particularly the Levant basin, shows a capacity of hosting tropical-subtropical benthos elements, a capacity not shared by the rest ofthc basin. The post—glacial Levant basin is in fact defined a qGodot basinq due to its present oceanographic prerogatives. It has been a potential receptacle of tropical organisms, yet could exploit such potentiality only after casual man induced events. Traditional and more recent niche concepts can be used to better understand the phenomenon of such biological invasions. Alien species successfully colonize the Godot basin, only when several conditions are favourable. Lower diversity, possibly related to resources not efficiently exploited by autochtonous. oFFers “niche opportunitiesq to the newcomers. In the particular case of the Lessepsian invasion, the success probably depends on finding dte appropriate time for colonization. This can account for the massive initial invasion and the steady increase of records witnessing a still ongoing process. INTRODUCTION From the biogeographefs perspective the Levant Basin (LB) is a unique laboratory to study one of the most impressive on—going marine colonization observable by man: the Lessepsian invasion (“migtations”, sensu Pot, 1971; see also e.g. Pot, 1975, 1978, 1990; Pot and Dimentman, 1989; Zibrowius, 1991, 1994, Ribera, 1993; Galil, 1993). In fact, wide sectors of the eastern Mediterranean Sea are being invaded by tropical—subtropical species both throughout the Suez