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Genetic diversity tes a th ic re obb tur invasive species. 2009 Elsevier Inc. All rights reserved. the fo undam ing im us eco of invasion are usually not recorded. This situation is even more challenging in the marine environment, where direct observations are logistically complicated and few systems are amenable to investigation. Yet, one marine system seems to be ideal for the study of marine bioinvasions: the Mediterranean Sea. all studied species were early Lessepsian migrants (first Mediterranean record between 1902 and 1964) one simple explanation was that the lack of genetic bottleneck resulted from multiple invasions, which slowly built up the genetic diversity observed in Mediterranean populations (Bucciarelli et al., 2002; Hassan et al., 2003; Hassan and Bonhomme, 2005; Azzurro et al., 2006). This explanation was also consistent with the ex-treme bottleneck observed in F. commersonii, a very recent inva-der (first observed in 2000), where only two haplotype