Based on the individual growth, food limitation, population renewal through seeding, and individual marketable
size, a theoretical model of the cultured species population dynamics was used to assess the carrying capacity of an
ecosystem. It gave a domeshape
curve relating the annual production and the standing stock under the assumption
of individual growth limited by the available food in an ecosystem. It also showed the influence of mortality rate
and marketable size on this curve and was introduced as a means to explore the global properties resulting from the
interactions between the ecophysiology of the reared species and the environment at the ecosystem level.
In a second step, an ecosystem model was built to assess the carrying capacity of MarennesOl
´eron bay, the most
important shellfish culture site in France, with a standing stock of Crassostrea gigas around 100 000 tonnes fresh
weight (FW) and an annual production of 30 000 tonnes FW. The ecosystem model focused on the oyster growth
rate and considered the interaction between food availability, residence time of the water, oyster ecophysiology and
number of individuals. It included a spatial discretization of the bay (box design) based on a hydrodynamicmodel,
and the nitrogen or carbon cycling between phytoplankton, cultured oysters, and detritus. From simulations of the
oyster growth with different seeding values, a curve relating the total annual production and the standing stock was
obtained. This curve exhibited a dome shape with a maximum production corresponding to an optimum standing
stock. The model predicted amaximum annual production of 45 000 tonnes FWfor a standing stock around 115 000
tonnes FW. The prediction confirmed some results obtained empirically in the case of MarennesOl
´eron bay and
the results of the theoretical model. Results were compared with those obtained in Carlingford Lough (Ireland)
using a similar ecosystem model. Carlingford Lough is a small intertidal bay where the same species is cultured at
a reduced scale, with current biomass less than 500 tonnes FW. The model showed that the standing stock can be
increased from 200 tonnes FW to approximately 1500 tonnes FW before any decrease of the production