*2.2. Conservation Status*

At the level of the Mediterranean Sea, it is estimated that there are 153 populations [36], and the species is reported at 137 Natura 2000 sites, of which 109 are priority coastal lagoon habitats. In Italy, populations are recovering and in good condition [33], but the state of conservation at the international level is considered unfavourable/inadequate, although the species is not at risk of threat [37].

According to Natura 2000 dataset (Table 3), in Italy, *A. fasciatus* is present in 72 coastal lagoons, with a heterogeneous distribution. The populations of the northern Adriatic Sea are distributed in the lagoon systems from the Isonzo estuary to the Pialassa lagoon and appear constant over time but distinct from each other [33,38], with a highly variable density; in fact, depending on the season and local morphological structures, the density can range, as in the case of the Venice lagoon, from 2 ind/100 m<sup>−</sup><sup>2</sup> in salt marsh areas strongly influenced by tides to 205 ind/100 m<sup>−</sup><sup>2</sup> in almost-closed artificial ditches [28]. In the southern Adriatic Sea, two distinct populations, one in the northern and the other in the southern Apulia zone, may be the result of channelling works that have fragmented the habitats and created inhospitable intermediate areas [33]. Along the Tyrrhenian coast, it is present in Tuscany and partially in Latium, and it is believed that the absence of *A. fasciatus*, between Latium and Campania, may be the consequence of extensive land reclamation conducted in the first half of the 20th century [33]. *A. fasciatus* surely disappeared from several inland waters, where it was reported in the 1800s and until 1980, and recently it has been observed only in Sicilian ones [33,39]. Past and present data on its distribution and abundance in rivers are scarce, but it is supposed that *A. fasciatus*, although it can survive in freshwaters, has little affinity for this habitat [33]. In fact, freshwaters host a more diverse community than brackish zones, where more constraining conditions limit the taxonomic richness [40], and *A. fasciatus* was demonstrated to suffer from the presence of other species and to prefer marginal and isolated zones [28,33]. Moreover, in recent years, the freshwater species *Gambusia holbrooki* (order Cyprinodontiformes, family Poeciliidae) has determined the extinction of some *A. fasciatus* populations in Northern Italian rivers [33,39]. This invasive species was demonstrated to be highly aggressive in oligohaline waters, but to be less successful at higher salinity [41,42], inducing species that can tolerate wide salinity variations to move towards brackish waters.

Despite the reduction of the range in freshwaters, in the original brackish and coastal environments, there has been a recovery of *A. fasciatus*, with the reappearance of populations considered extinct, especially in the northern Tyrrhenian coast [33]. The factors favouring the recovery are unknown, but the most probable reason seems to be the reappearance of wetlands and the establishment of protected areas, including transitional water bodies [33].

In the Greek Porto Lagos lagoon, the relative abundance of *A. fasciatus* reached almost 10% of the ichthyofauna community, with catch per unit e ffort (CPUE) from 5 in May 1989 to 1572 in October 1989 [43]. More recent studies, also in other Greek lagoons, describe population dynamics and structure, but they do not report density or abundance data. However, considering the number of specimens caught during these studies, it can be supposed that the populations are rather abundant [19,21,23].

In Cyprus Akrotiri wetlands, *A. fasciatus* was demonstrated to have a "contraction-expansion" distribution depending on the annual hydrology. Based on observations between 2008 and 2015, the species' range was significantly contracted and, in 2016, the CPUE ranged from 12 to 931 [44].

In Croatia, until the early 2000s, the species was reported in several sites, while more recently, it has been found only in half of the historical basins. However, some new findings were recorded and some other habitats have to be investigated. The data available indicate that the distribution is discontinuous along the entire eastern Adriatic coast and the captures tend to be rather low [45].

Depending on the colonization range, the main, but not unique, threats for *A. fasciatus* are:

