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- Mathematical modelling to assess the carrying capacity for multi-species culture within coastal watersPublication . Duarte, Pedro; Meneses, R.; Hawkins, A.J.S.; Zhu, M.; Fang, J. G.; Grant, J.In the context of aquaculture, carrying capacity is generally understood as the standing stock of a particular species at which production is maximised without negatively affecting growth rates. The estimation of carrying capacity for aquaculture is a complex issue. That complexity stems from the many interactions between and among cultivated and non-cultivated species, as well as between those species and their physical and chemical environments. Mathematical models may help to resolve these interactions, by analysing them in a dynamic manner. Previous carrying capacity models have considered the biogeochemical processes that influence growth of cultivated species in great detail. However, physical processes tend to have been addressed very simplistically. Further, most modelling has been for monocultures, despite the increasing importance of multi-species (=polyculture) systems. We present here a two-dimensional coupled physical–biogeochemical model implemented for Sungo Bay, Shandong Province, People’s Republic of China. Sungo Bay is used for extensive polyculture, where bivalve shellfish and kelp are the most important cultivated species. Data collected over 13 years (1983–2000)was available for modelling. Our main objectives were to implement the model, achieving reasonable calibration and validation with independent data sets, for use in estimating the environmental carrying capacity for polyculture of scallops and oysters. Findings indicate that the model successfully reproduces some of the main features of the simulated system. Although requiring some further work to improve predictive capability in parts, predictions clearly indicate that Sungo Bay is being exploited close to the environmental carrying capacity for suspension-feeding shellfish. Comparison of different culture scenarios also indicates that any significant increase in yield will depend largely on a more optimal spatial distribution of the different cultivated species.
- Trophic capacity of Carlingford Lough for oyster culture – analysis by ecological modellingPublication . Ferreira, João; Duarte, Pedro; Ball, B.A one-dimensional ecosystem box model is presented for carrying capacity assessment.The model includes physical and biological processes. The physical processes are the transport of nutrients, suspended matter and phytoplankton through the system boundaries and between model boxes. The biological processes are primary production and oyster (Crassostrea gigas) population dynamics and physiology. The model was implemented using an object oriented approach. The model was employed to estimate the carrying capacity of Carlingford Lough (Ireland) for oyster culture. In the Lough, low water temperatures prevent the oysters from reproducing. Therefore, recruitment is human dependent. Small oyster spat is seeded every year during spring and harvested after the summer of the next year. During this period oysters reach commercially harvestable weight. The results obtained indicate that the carrying capacity of this system is approximately 0.45 g oysters (AFDW) m-3, determined more by the availability of particulate matter than by phytoplankton. It is suggested that a fivefold increase in oyster seeding may optimise harvest yield.
- Modelling Local Food Depletion Effects in Mussel Rafts of Galician RiasPublication . Duarte, Pedro; Labarta, Uxio; Fernández-Reiriz, Maria José; yesMollusc culture is one of the most important types of mariculture, with suspension feeding bivalves being among the most cultivated organisms. In the last years, there has been a growing concern about carrying capacity (CC) of natural ecosystems for bivalve culture, because of decreases in growth rates and mass mortalities due to overstocking. Several methods have been proposed for CC estimation. The simplest are based on average properties integrated over various time scales, like water renewal rate, phytoplankton primary production and bivalve clearance rate. If the time scale of the former two processes is larger than the time scale for bivalve filtration than, bivalve standing stock is over ecosystem CC. More complex approaches are based on ecosystem box modelling or coupled physical-biogeochemical models. The objective of this work is to evaluate production CC for mussel rafts in Galician Rias as a function of mussel loads and current velocities. For this purpose an analytical model was developed and used to find conditions that maximize raft production. Obtained results suggest that CC at the raft scale has not been exceeded by current culture practices. However, it does not seem advisable to increase mussel loads per raft. Therefore, any possible increase in mussel production should be considered at a higher spatial scale.