Deep Bay is a shallow estuary covering an area of around 115 km2 located to the north of the New Territories of Hong Kong and to the south of the city of Shenzen, China. Its waters are home to a major aquaculture industry for the Hong Kong oyster, Magallana hongkongensis, cultivated on rafts.
The significant increase of oyster rafts in recent years has affected the coastal environment, highlighting the need to strengthen the management of oyster farming activities in the area. In this context, a comprehensive assessment of the ecological dynamics of Deep Bay was carried out with the objective of quantifying the bay’s environmental carrying capacity and determine the optimal level of production in the different aquaculture zones. An integrated soil to sea modelling framework was developed and applied to Deep Bay (Fig. 1).
The framework combines the simulation of (i ) land-based loads with the Soil and Water Assessment Tool (SWAT) catchment model; (ii) hydrodynamics of the Deep B ay using the Regional Ocean Modeling System (ROMS) model; (iii) and the Magallana hongkongensis individual growth model. All three components are included within the well-tested EcoWin ecological model (e.g. Ferreira et al, 2008; Bricker et al. 2018, and references therein).
The EcoWin model domain applied to Deep Bay was divided into 17 horizontal boxes and 2 vertical layers totalling 34 individual computation units, using a multicriteria approach based on administrative boundaries, physics, and water quality. In parallel, detailed mapping of the 10,000 rafts, with a total capacity of around 500 million oysters, was carried out to parameterise spatial distribution and stocking density of oyster farming (Fig. 2).
The EcoWin model was calibrated and validated against field measurements and is able to reproduce the observed ranges and seasonal patterns of nutrients and particulate matter concentrations. The implementation of an individual growth model specific to Magallana hongkongensis and the ability of the EcoWin model to simulate management scenarios such as different stocking densities, seeding and harvest sizes and periods, and mortality, provide an integrated framework for supporting local stakeholders and policy makers with respect to management options for oyster aquaculture in Deep Bay. We present estimates for the carrying capacity of Deep Bay for oyster culture, the effect of top-down control on eutrophication in the bay, and discuss options for optimisation of bivalve aquaculture, taking into account the suitability of different areas, the harmonisation of different water uses, and the role of different actors in the bay ecosystem, including conservation interests.
References
Bricker, S.B., Ferreira, J.G., Zhu, C., Rose, J. M., Galimany , E., Wikfors , G., Saurel, C., Miller, R. L., Wands, J., Trowbridge, P., Grizzle, R., Wellman, K., Rheault, R., Steinberg, J., Jacob, A., Davenport, E. D., Ayvazian, S., Chintala, M., Tedesco, M. A., 2018. Role of Shellfish Aquaculture in the Reduction of Eutrophication in an Urban Estuary. Environ. Sci. Technol. 52:173–183. https://doi.org/10.1021/acs.est.7b03970
Ferreira, J.G., Hawkins, A.J.S., Monteiro, P., Moore, H., Service, M., Pascoe, P.L., Ramos, L., Sequeira, A., 2008. Integrated Assessment of Ecosystem-Scale Carrying Capacity in Shellfish Growing Areas. Aquaculture, 275, 138-151.