Plasticity in habitat use of two native Ponto-Caspian gobies,

The Ponto-Caspian region is an important source area for some invasive gobiid fishes. These fishes have colonised several freshwater ecosystems in Europe, as well as in North America. As knowledge on their habitat utilisation in their native range remains limited, the seasonal habitat uses of Western tubenose goby, Proterorhinus semilunaris and monkey goby Neogobius fluviatilis were studied in four natural lakes in the Marmara Region (NW Turkey). Habitat use of both species was highly variable between the lakes and seasons, with P. semilunaris showing higher plasticity. In general, the main habitats used by P. semilunaris were shallow waters in littoral areas that had vegetation cover, whereas N. fluviatilis consistently used sandy substratum in deeper waters that lacked vegetation. These results suggested there was high plasticity in the habitat utilisation of these two gobiids, especially in P. semilunaris, which potentially facilitates their ability to establish and invade novel environments. The habitats that are especially vulnerable to P. semilunaris invasion are medium size substrates which provide individuals with sufficient interstitial space for refuge. Waters providing differing habitats, such as sandy substrata, might inhibit their colonisation, but are potentially more vulnerable to N. fluviatilis invasion.