Invasive Species In Mediterranean Sea

. Introduction

Mediterranean is a semi-enclosed sea which originated from a big ocean known as the Tethys about 200 million years ago (mya). Remnants of the Tethys and some geological events have formed the today’s biodiversity of Mediterranean Sea. Now, Mediterranean Sea is seen as a ‘biodiversity hotspot’ covering 4%-18% of the world marine species (Bianchi and Morri, 2000; Myers et al., 2000). However, 5% of the all Mediterranean marine species are alien. According to IUCN (2000), alien species, also known as introduced, non-native, exotic or non-indigenous species, is a taxonomic group which exists outside of their native geographical range. When an alien species establishes and eventually spreads in a non-native environment, it can become

There are four main reasons for existence and dispersion of invasive species in the Mediterranean Sea. These are Atlantic inflow, lessepsian migration (i. e. species comes from Red Sea and Indian Ocean via Suez Canal), human mediated introduction and climate change (rising sea temperature). While the first three causes act as resources of alien species, climate change is like a mechanism favoring biological invasions (Bianchi, 1997). It is well known that physical conditions of the environment affect species’ distribution. In semi-enclosed seas like Mediterranean, it was predicted that sea bottom temperatures and sea surface temperatures increased faster than neighboring open sea temperatures (Cheung et al., 2009). It was probably the first area where the temperature changes were associated with global warming (Béthoux et al. 1990). In the Mediterranean Sea, surface temperature has increased by 1oC between 1974–2004 (Salat and Pascual, 2002). Furthermore, according to estimates based on different scenarios, all the Mediterranean coastal sea temperatures will increase between 1 and 2.5 degrees at the end of the 21st Century (Di Carlo and Otero,

Therefore, indirect effects of climate fluctuations take place more easily in these ecosystems. In some extreme perturbations, climate-induced invasions may cause the transformation of the ecosystems as invasive species displace native species. The high tolerance of invasive species may lead to collapse of native species (Mack et al., 2000; Gritti et al., 2006). Although some examples for replacement of native species by alien species have shown, there is no evidence on the extinction of native species due to non-native species. Therefore, non-native species are added to native species and number of species in the Mediterranean increases (Boudouresque, 2004; Boero and Bonsdorff, 2007). One can understand this species richness as a positive effect of introduction and establishment of alien species, particularly for the eastern area where species are less abundant; however, these species may lead to homogenization of biota (Ricciardi, 2007), increase the regional extinction risk of native species, decrease genetic diversity and change the marine habitat and ecosystems (CIESM,