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exotic species combine to cause loss of biodiversity through biotic homogenization:
endemic species unable to tolerate the alteration of the ecosystem (the `losers') will
get extinct, exotic species transported by man (the `winners') will expand their
geographic range (McKinney, 1999).
According to Zenetos et al. (2012) the definition of an alien, non-indigenous,
exotic, non-native or allochthonous species is defined by its presence in the wild,
through introduction outside its natural range and beyond its natural dispersal
potential. In the last decade, the establishment in marine ecosystems of invasive
alien species (i.e., non-indigenous species having an adverse effect on biological
diversity, ecosystem functioning, socioeconomic values and/or human health in
invaded regions: Olenin et al., 2011) has rapidly become a central environmental
issue (Ruiz et al., 2000; Grosholz, 2002; Occhipinti- Ambrogi, 2007; Galil et al., 2009;
Walther et al., 2009; Occhipinti- Ambrogi and Galil, 2010).
With few exceptions, the ecological impact of invasive alien species on the
native Mediterranean biota is poorly known (Zibrowius, 1991; Boudouresque, 2004),
though it is believed that keystone invasive species may cause major shifts in
community composition. The impacts of invasive alien crustaceans often reflect in
changes in the trophic structure of native communities, and, in turn, on energy flows
through the ecosystem (Hanfling et al., 2011; Mancinelli et al., 2013).
Impact of invasive species has been defined by Parker et al. (1999), who also
discussed a variety of measures of impact. In the marine environment, Ruiz et al.
(1999) also describe impact by alien species and interactions with other stress
factors. The impact of these species on native communities has been evaluated in
many localities all over the world leading to the concept of biotic pollution. This is
especially evident in the Mediterranean Sea (Occhipinti-Ambrogi, 2007). Similarly
Elliot (2003) observes that there are many aspects in which introduced marine
organisms can be regarded as being no different from chemical pollutants and
encourages the use of the term biological pollution.
Indo-Pacific species (of warm water affinity), established in different phases
after the opening of the Suez canal, have caused changes in the Levantine part of the
Mediterranean far beyond recorded impacts in other marine ecosystems. Nearly half
of the fish catches along the Israeli coast consist of Indo-Pacific species (Goren and
Galil, 2005). The process has accelerated in recent years, with increasing records of
newly discovered Indo-Pacific species and expansion towards other areas of the
Eastern (Galil and Zenetos, 2002) and Western Mediterranean (Harmelin-Vivien et
al., 2005; CIESM, 2005). The unabated influx of the Indo-Pacific biota is rooted in the
continuous enlargement of the Suez Canal that has altered its hydrography and
hydrology, and enhanced its potential as a ‘‘corridor’’ allowing ever greater numbers
of organisms through.
The most notorious and best studied invasive species in the Mediterranean
are the coenocytic chlorophytes: Caulerpa taxifolia (Meinesz et al., 2002), and
Caulerpa racemosa (Verlaque et al., 2004). Other studies traced the impacts of
invasive aliens that entered the Mediterranean from the Red Sea through the Suez
Canal (Por, 1978; Golani, 1998; Galil, 2000, 2006; Goren and Galil, 2005). It had been
suggested that most invasive aliens, are part of a synergetic complex of drivers
where ‘‘habitat disturbance frequently increases the impacts of invasive species’’
(Didham et al., 2005; MacDougall and Turkington, 2005).