Study of the fish fauna on the rocky outcrops in the Gulf of Trieste.

Trezze are are rocky oases emerging on a homogeneous and monotone bottom, mostly formed by sand and mud. The presence of cavities and interstices in hard substrata causes an increment of micro-habitats and ecological gradients, which increases the specific diversity of marine organisms populations. The environmental, ecological and productive value of the trezze environment is, thus, high. However, it is a fragile environment, due to its calcareous and porous nature.

In consideration of the enormous heterogeneity of these substrata and the scarcity of local knowledge, we carried out an integrated and coordinated research among different geological and biological aspects of these particular habitats. The Fondazione Cassa di Risparmio di Gorizia and the Cassa di Risparmio di Udine e Pordenone, with the support of the Comune of Grado and the Comune of Lignano Sabbiadoro, financed a reasearch project on the rocky outcrops of  the Northern Adriatic. Partners in the reasearch were: OGS (RIMA and BiO Departments), Osservatorio Alto Adriatico of ARPA F.V.G., the Department  of Life Science and the Department of Geoscience of the University of Trieste and the Marine Protected Area of Miramare.

OGS carried out the characterization of nektonic populations by experimental fishing, using a low-impact gear in the vicinity of the rocky outcrops. Fishing trips were performed in cooperation with local professional fishermen, exploiting their knowledge of the sites. Sampled organisms were determined, measured and sorted by areas; all species of fishes, crustaceans and molluscs were considered.

Results about experimental fishing were supported by the description of the professional fishing activities. This produced valuable information for a sustainable management of these sites and, by direct participation of fishermen, increased their sensibility towards these particularly fragile environments.

Part of the results of the research is published on the volume “Trezze or grebeni: biotopes and geotopes of the Northern Adriatic” financially supported by the Friuli Venezia Giulia Region.