Aquaculture-induced boundary circulation and its impact on coastal frontal circulation

Abstract

With the development of coastal suspended aquaculture industry, aquaculture facilities have extended into the open sea to depths of up to 30 m. This practice will likely affect the natural ocean circulation in such areas. For a case study in the high-density aquaculture region of the coastal Yellow Sea, an aquaculture-induced boundary circulation (ABC) is identified and its effects on the background frontal circulation and cross-shore nutrient supply are examined. The ABC is composed of a southward along-boundary current and a counterclockwise cross-boundary cell. The southward along-boundary current (∼5 cm s −1 ) along with the natural frontal current (∼5 cm s −1 ) forms a strong coastal current (∼10 cm s −1 ) along 20-30 m isobaths. The counterclockwise cross-boundary cell exhibits the opposite direction to the natural clockwise cross-frontal cell in the frontal area, which reduces the cross-shore nutrient supply by nearly 25%. Our results suggest that aquaculture boundaries and densities should be considered when planning high-density aquaculture activities.

Influence of Suspended Aquaculture on Hydrodynamics and Nutrient Supply in the Coastal Yellow Sea

“…Xuan et al. (2019) found that there is a counterclockwise cross‐boundary cell around the aquaculture boundary, with its magnitude exceeding the clockwise cross‐frontal cell generated by tidal fronts in natural conditions. The weakened onshore currents within lower layers may significantly reduce the nutrient supply for the near‐bottom water at the aquaculture boundary, which carries higher nutrient concentrations.…”

“…A previous study (Xuan et al, 2019) pointed out that tide-induced water convergence is the major forcing in boundary circulation. The sea surface height on the inshore side of the aquaculture boundary is much higher than that on the offshore side because of the strong friction in the aquaculture area, suggesting that water converges on the inshore side of the aquaculture boundary.…”

“…Since it acts as the boundary between two water masses of different thermal, biological, and chemical compositions, the circulation around the fronts has important implications in the mass and energy exchange between the two different water masses. Previous analytical and numerical models (Dong et al., 2004; Loder et al., 1993; Lü et al., 2010; Simpson & Hunter, 1974; Su & Huang, 1995; Van Heijst, 1986; Xuan et al., 2019) have revealed that a clockwise cross‐frontal cell (blue curves with arrows, Figure 1c), which was driven by a vertical pressure gradient, was established with upward vertical velocities on the light (warm) side and downward vertical velocities on the heavy (cold) side. Since the Yellow Sea cold water mass is considered a nutrient‐rich pool, the upwelling component of cross‐frontal cells plays a vital role in nutrient supply and triggers phytoplankton growth in coastal waters (Li et al., 2006; Xin et al., 2015; Zhu et al., 2018).…”

Growth and survival of milkfish (Chanos chanos), tiger prawns (Panaeus monodon), and oysters (Crassostrea sp.) in integrated multi-trophic aquaculture (IMTA) system with varying stocking densities

“…The more food supplies in the water, the faster the growth. In addition, water currents play an important role in the success of culture activities in both water circulation and nutrient transport (Xuan et al, 2019).…”