The development of shellfish farming was analyzed with a coupled watershed and 3D biogeochemical model for the Sacca di Goro coastal lagoon (Northern Adriatic Sea, Italy). Sacca di Goro is the second site in Europe for the production of the Manila clam (Tapes philippinarum). Different scenarios were identified and analyzed, considering clam productivity under different environmental conditions, namely with and without macroalgal blooms. In addition, the influence of climatic variability - dry, average and wet years - was assessed. Model simulations indicated that macroalgal blooms have an important negative impact on clam productivity due to the risk of anoxia and subsequent clam mortality. Furthermore, simulation results evidenced that meteorological conditions also affect clam productivity, especially in a dry year due to a shortage of food supply. © 2007 Elsevier B.V. All rights reserved.