**Lagoon Resident Fish Species of Conservation Interest According to the Habitat Directive (92**/**43**/**CEE): A Review on Their Potential Use as Ecological Indicator Species**

### **Chiara Facca \*, Francesco Cavraro, Piero Franzoi and Stefano Malavasi**

Department of Environmental Sciences, Informatics and Statistics, Ca' Foscari University of Venice, via Torino 155, 30175 Venice, Italy; cavraro@unive.it (F.C.); pfranzoi@unive.it (P.F.); mala@unive.it (S.M.)

**\*** Correspondence: facca@unive.it; Tel.: +39-(0)-41-234-7733

Received: 22 May 2020; Accepted: 17 July 2020; Published: 20 July 2020

**Abstract:** Transitional waters are fragile ecosystems with high ecological, social and economic values, that undergo numerous threats. According to the information provided by European Member States in the framework of the European Directive 92/43/EEC (Habitat Directive), the main threat to these ecosystems is represented by morphological and hydrological changes. The present work focuses on six lagoon fish species included in the Habitat Directive annex II (species requiring conservation measures: *Aphanius fasciatus*, *A. iberus*, *Knipowitschia panizzae*, *Ninnigobius canestrinii*, *Valencia hispanica* and *V. letourneuxi*) that spend their entire life cycle in the Mediterranean priority habitat 1150\* "Coastal lagoons". The overview of the current scientific literature allowed us to highlight how the presence and abundance of these species may provide important indications on the conservation status of coastal lagoon habitats. In fact, their occurrence, distribution and biology depend on the presence of peculiar structures, such as salt marshes, small channels, isolated pools and oligohaline areas. Coastal lagoon fragmentation and habitat loss have led to a significant reduction in genetic diversity or local population extinction. Although *Aphanius* and gobies have been shown to survive in eutrophic environments, it is clear that they cannot complete their life cycle without salt marshes (mainly *Aphanius*) and wetland areas (mainly gobies).

**Keywords:** coastal lagoon; morphological alterations; habitat conservation; killifishes; gobies; Mediterranean Sea
