1st International Congress on Environmental Modelling and Software - Lugano, Switzerland - June 2002
Keywords
bioeconomic analysis, stochastic model, algal blooms management, tapes philippinarum
Start Date
1-7-2002 12:00 AM
Abstract
During the last twenty years the economic activity of clams exploitation has been intensively developed in the southernmost coastal lagoon of the Italian Po river delta, Sacca di Goro. Still, clam breeding is in danger because of frequent summer algal blooms, due to Ulva rigida macroalgae. These blooms cause anoxic crises leading clams to collapse, with a consequent deep impact on the whole economic sector of clams exploitation. Several strategies have been developed to avoid the loss of commercial production, yet none of them has been assessed on a mathematical basis. In this work we develop a simple stochastic mathematical model of Ulva rigida growth to quantitatively evaluate the economic costs of algal harvesting and the related benefits in terms of avoided ‘economic loss’ of clams production due to an effective prevention of algal blooms. Algal growth is simulated by means of a discrete time difference equation of Ulva rigida biomass where the finite growth rate depends only upon water temperature. In order to explicitly include environmental variability, a seasonal autoregressive model calibrated on available data is used to simulate water temperature. By means of Monte Carlo simulations, different harvesting strategies are analysed in terms of the number of harvesting vessels employed and the threshold biomass of Ulva rigida at which vessels start to operate. In particular, with reference to previous works by the same authors, more realistic harvesting functions are estimated, taking into account the effects of reduced efficiency of the vessels in the case of low density of Ulva rigida biomass. Also costs of algal harvesting and disposal, as well as monetary damages resulting from the collapse of clam production as a consequence of algal blooms, are refined.
The control of algal bloom damages to clam yield in a North Adriatic coastal lagoon (Sacca di Goro, Italy)
During the last twenty years the economic activity of clams exploitation has been intensively developed in the southernmost coastal lagoon of the Italian Po river delta, Sacca di Goro. Still, clam breeding is in danger because of frequent summer algal blooms, due to Ulva rigida macroalgae. These blooms cause anoxic crises leading clams to collapse, with a consequent deep impact on the whole economic sector of clams exploitation. Several strategies have been developed to avoid the loss of commercial production, yet none of them has been assessed on a mathematical basis. In this work we develop a simple stochastic mathematical model of Ulva rigida growth to quantitatively evaluate the economic costs of algal harvesting and the related benefits in terms of avoided ‘economic loss’ of clams production due to an effective prevention of algal blooms. Algal growth is simulated by means of a discrete time difference equation of Ulva rigida biomass where the finite growth rate depends only upon water temperature. In order to explicitly include environmental variability, a seasonal autoregressive model calibrated on available data is used to simulate water temperature. By means of Monte Carlo simulations, different harvesting strategies are analysed in terms of the number of harvesting vessels employed and the threshold biomass of Ulva rigida at which vessels start to operate. In particular, with reference to previous works by the same authors, more realistic harvesting functions are estimated, taking into account the effects of reduced efficiency of the vessels in the case of low density of Ulva rigida biomass. Also costs of algal harvesting and disposal, as well as monetary damages resulting from the collapse of clam production as a consequence of algal blooms, are refined.
