DISTRIBUTION AND ECOLOGICAL PREFERENCES OF THREE GOBY SPECIES IN THE ISONZO RIVER MOUTH (NORTHEAST ITALY)

River mouths coastal habitats (in transitional zones between terrestrial and marine systems) usually show high levels of habitat heterogeneity and have great value for fish communities, because of their pivotal role as spawning, nursery and feeding areas or as pathways in migration processes. In these ecosystems, species belonging to the family Gobiidae (Teleostei) are commonly observed and differently distributed according to the chemical and physical water parameters and substrate characteristic. The family includes species of Community interest, listed in Annexes of Habitat Directive 92/43/EEC and therefore it is important to improve knowledge about these fishes, to provide useful information for conservation and management policies. The present work analyzes distribution and ecological preferences of three species: the marbled goby Pomatoschistus marmoratus (Risso, 1810), the black-spotted goby Pomatoschistus canestrinii (Ninni, 1883), and the lagoon goby Knipowitschia panizzae (Verga, 1841). P. canestrinii and K. panizzae, are listed in the Annex II of the Habitat Directive 92/43/EEC. Thes study was carried out inside the Natural Reserve of the Isonzo River mouth (Friuli-Venezia Giulia), the northernmost wetland in the Mediterranean Sea, included in a special area of conservation (SAC IT3330005) and in a Special Protection Area (SPA IT3330005). After a preliminary exploration in early June 2019, 15 sampling points were chosen, based on abiotic features such as salinity/water conductivity, substrates, vegetation cover, depth, and persistence of water. Five sampling campaigns were carried out from late June 2019 to January 2020: fish specimens were collected with a dragnet and values of water chemico-physical parameters were measured using portable field instruments. Water temperature (°C), pH, and conductivity (mS cm-1) were considered, while substrate characteristics and vegetation cover were also recorded. An amount of 289 individuals were collected: 66.44% were identified as P. marmoratus, 18.34% as K. panizzae and 14.19% as P. canestrinii. The latter species was recorded in the area for the first time, as its presence was only theoretically assumed before the present study. Analyses carried out with Canonical Correspondence analysis highlighted that the investigated species showed different ecological preferences: P. marmoratus was confirmed to be a generalist species, adapting to a wide gradient of salinity, temperature, and pH, but slightly favoring unvegetated and coarse substrates, with moderate salinity levels, as reported by other works on the species. K. panizzae was found to dominate the brackish, calm waters with fine substrates such as mud, and moderate vegetation cover. Finally, the distribution of P. canestrinii was found to be highly influenced by water conductivity, substrate size and the vegetation cover, as the species showed clear preferences for freshwater habitats with coarse substrates and scarce vegetation. P. canestrinii is an endemism of the Northern Adriatic Sea and a species of Community interest, and data about its presence and distribution could be of great interest and may have important implications in the management and conservation plans.