Effects of Beach Nourishment on Donax trunculus in the Latium Coasts (Central Tyrrhenian Sea, Italy)

During the last decade, beach nourishments using relict sands were carried out on some beaches located in Latium (Central Tyrrhenian Sea, Italy). In this coastal environment, some important economic resources as the bivalvia Donax trunculus (Linnaeus, 1758) are typically found. D. trunculus is a very common bivalve on the Mediterranean sandy beaches and constitutes a very important fishing resource. This species is extremely sensitive to the sediment grain size variations during its lifespan. A monitoring study was performed to evaluate the effects of beach nourishment using relict sands (carried out in 2003) on D. trunculus populations in three beaches along the Latium coasts: two of the beaches were interested by nourishment and a third one, in sedimentary equilibrium, was used as a control site. Surveys were realized, from June 2002 to March 2004, before, during and after beach nourishment. Data showed a temporal and spatial variation of Donax densities related to the granulometric changes of sediments. Results showed that after the beach nourishment, specimens, when present, died buried by the new settled sediments. In the two nourished beaches in a few months (3-4), after a period of sediment re-equilibration, several juveniles were observed with an increase of densities related to the recruitment period. The occurrence of Donax juveniles after nourishment has been observed also where D. trunculus populations were previously absent. Results highlighted the importance to know the biology of the main littoral species in order to evaluate the effects of beach nourishment using relict sands. Therefore it is possible to hypothesize that planning beach nourishments in a specific period, possibly before the juvenile recruitment, effects on the marine environment would minimize, avoiding also significant economic relapses on the local fishery.