Growth of the longline-cultured Pacific oyster Crassostrea gigas in a temperate bay: A model simulation based on scope for growth

Abstract

The growth of longline-cultured Pacific oyster crassostrea gigas was simulated based on scope for growth (SFG) model in Geoje-Hansan Bay off the southern coast of Korea. We set parameters of model functions based on environmental data and biometric and physiological measurements of oysters cultured in suspension in the bay from July 2013 to February 2014, simplifying the structure of SFG-based oyster growth model compared with those of the commonly-adopted intertidal model. In our SFG-based growth models, two forcing variables of seawater temperature and food density were applied to the growth processes of oysters. We also tested oyster growth in response to two indices of available food: chlorophyll a (Chl a) and food energy concentrations. Our simplified model predicted well the overall growth of longline-cultured oysters in Geoje-Hansan Bay. While Chl a and food energy concentrations were lower in the outer-bay than in the inner-bay sites, the observed dry tissue weights (DWs) of oysters at the initial and final stages of cultivation were consistent between sites. Simulation modeling pointed out that such a spatially consistent growth performance reflect an enhanced food ingestion due to the lowered half-saturation coefficients (X_k) in the outer bay compared with the inner bay. The oyster DW simulations based on the Chl a and food energy concentrations as food indices (Chl a- and food energy-simulations) were well fitted with the observed DWs in the outer-bay site. In contrast, in the inner-bay site, oyster DWs estimated by the Chl a- and food energy-simulations showed a good agreement with the observed DWs at the early growing stage and the late stage of cultivation, respectively. Such a discrepancy in the oyster DWs simulated by different food indices may be explained by temporal shifts of the phytoplankton community (the dominance of diatoms vs. microflagellates) in the inner bay.