Invasive Alien Species in the Mediterranean Sea: The Case Study of Caulerpa cylindracea

The Not Indigenous Species, named NIS, widespread in the Mediterranean Sea, penetrated into the basin just from the first decades of last century because of maritime navigation across Suez canal and Gibiltar strait connecting Indian and Atlantic oceans with Mediterranean basin [1]. In this way, the building of Suez canal, realized by Ferdinand de Lesseps, the reduction of the salinity levels in bitter lakes but, most of all, the doubling of the canal happened in 2015 [2], favoured the transit of many vegetal and faunal alien species from Indo-Pacific region to the Mediterranean one, that completely changed its geographical pattern from a semi-enclosed to a semi-opened basin, prone to a busy commercial navigation coming from the Red Sea. Indeed, the Mediterranean Sea has become very sensitive to biological invasions caused by many tropical alien species, entering into the basin. This process fostered also by the global warming of Mediterranean seawaters caused in time the entrance of allochthonous and thermophic species spreading into the Mediterranean waters through “fouling” communities and ballast waters of ships and boats in transit along this important waterway for trading activities [3]. Amongst NIS, some plant and faunal species, after further phases of spreading and acclimatization, were completely established in the seawaters of the basin, extending their populations in time. So, many Invasive Alien Species, named IAS [4], have established in Mediterranean seawaters and are actually able to affect the sensitive ecological balance and the right functioning of some marine ecosystems [5-9] (Figure 1).

Figure 1:The interactions of Invasive Alien Species (IAS) in the structure of Mediterranean marine biota.s

Actually, in Mediterranean seawaters live 247 IAS, of which 25 ones are marine macroalgae [10,11]. Amongst them, a green algae, named Caulerpa cylindracea Sonder1845 (hereafter C. cylindracea), has been classified as one of the first 100 worst invasive species [6] able to affect the plant biodiversity of Mediterranean Sea. Really, C. cylindracea shows a great environmental capacity thriving in different stations such as in exposed and sheltered sites, in shaded and sunny seawaters but, also, in pristine and in polluted coastal regions, from surface waters until 70 meters depth [12]. In this way, the spreading of the species could affect negatively the structure of marine biota or, otherwise, could increase its biodiversity, leading in time to new ecological niches (Figure 2).

Figure 2:The effects of biological invasions on coastal ecosystems.

Therefore, it is difficult to value the effects of this invasive process in the short and long time because it is yet unknown if the spreading of C. cylindracea could increase or decrease the Mediterranean marine biodiversity [13]. These doubtful conditions call for monitoring programs and mapping plans directed towards an effective management of the species, as highlighted by scientific literature [14-16]. Finally, it is necessary to ensure a close connection between scientists, policy makers, stakeholders and citizens so to realize an effective management of all the invasive processes occurring in Mediterranean Sea.

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