Rhopilema nomadicain the Mediterranean: molecular evidence for migration and ecological hypothesis regarding its proliferation

Since it was first observed in Israel in the 1970s, the ‘nomad jellyfish’ Rhopilema nomadica has established a reputation as one of the worst invasive species in the Mediterranean Sea. It was assumed to originate in the Red Sea, or in the Indo-Pacific region, but in the absence of additional reports of live specimens outside the Mediterranean, its origins remained a mystery. Here, via molecular analysis, we present the first verified results of the existence of R. nomadica in the Western Indian Ocean. Moreover, using additional evidence from Cassiopea andromeda and R. nomadica , we propose that the construction of the Aswan High Dam may have led to the proliferation of R. nomadica in the Levantine Basin.