| An ecosystem box model for estimating the carrying capacity of a macrotidal shellfish system (1994) | |||||||||||||
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| An ecosystem model is presented for estimating the shellfish carrying capacity of Marennes-Oléron Bay (France). It incorpora tes physical and processes: horizontal transport of suspended matter, feeding and growth of the cultivated oyster Crassostrea gigas and primary production. The precision and consistency of the model are tested by comparing simulations to observed data. The model smoothes both spatial and temporal variability suspended-matter concentratIons but reproduces me an levels and seasonal cycles with some accuracy. Carrying capacity of the shellfish system is assessed by computing the sensitivity of oyster growth to oyster abundance. Model results clearly indicate a density dependence of oyster growth. When stock is adjusted from 20 % to 200 % of the present value, maximal dry weight of oyster5 shows a mean decrease of approximately 25 %. The spatial heterogeneity of the growth response i5 a consequence of the low level of primary production within the shellfish area. The hydrodynamic regime of the bay strongly controls the carrying capacity of the shellhsh system: flushing time and available light energy are found to be 2 determining factors which prevent the phytoplankton from thriving in the bay: tidal currents ensure a fast renewal of food. Nevertheless. phytoplanktonic production accounts for a non-negligible part of food filtered by oysters and is identified as important food source when stock lev el low. The validity of the model is limited by present description of the physical transport of suspended and deposited matter. | |||||||||||||
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