Abstract : Alien species —sometimes termed exotic, introduced or non-native species— are plants and animals that have been intentionally or unintentionally introduced, established populations and spread into the wild in the new host region (IUCN, 2002). In their home environments, these species live in balance with their local native environment, and populations are controlled by ecosystem interactions such as predation, parasitization and disease. Alien invasive species (IAS) are alien species which become established in natural or semi-natural ecosystems or habitat, become an agent of change, increasing in abundance and distribution, and threatening native biological diversity” (IUCN, revised). IAS compete and on some occasions can replace native species, and cause complex changes within the structure and function of the new hosting ecosystem (Galil, 2007, 2009).
IAS are considered one of the main causes of biodiversity loss in the Mediterranean Sea (Galil, 2007, Coll et al., 2010) potentially modifying all aspects of marine and other aquatic ecosystems. They represent a growing problem due to unprecedented rate of introduction (Zenetos et al., 2010) and the unexpected and harmful impacts that they have on the environment, economy and human health (Galil, 2008).
This is a general phenomenon and extents to all regions of the Mediterranean (Galil, 2007, 2009; Zenetos et al. 2010). That is why invasive species are considered as “focal species” and should be monitored in all the regions (Pomeroy et al., 2004).
