Hydrodynamic effects of large-scale suspended mussel farms: Field observations and numerical simulations

Abstract

The hydrodynamic effects of the largest suspended mussel farms in the East China Sea near Gouqi Island, was investigated using a high-resolution 3D ocean model and field observations. To capture the 3D farm effects on hydrodynamics, an additional depth dependent momentum sink term was introduced in the model. The model results compared well with the field observations. The present model and observational results indicate that the presence of farms reduces the flow by more than 79%, 55%, and 34% in the upper, middle, and bottom layers at the farm center, respectively. According to the harmonic analysis of predicted current, mussel farms reduce the magnitude of the semidiurnal tidal current and also alter the magnitude and direction of the diurnal tidal current. The blockage by the farm weakens the Eulerian residual tidal current within the farm in the NE-SW direction, while strengthens that at the edge of the farm in the SE-NW direction. Cross sections, Sec1 and Sec2 are perpendicular to these two major residual currents and intercept with the center of the farm from SE to NW and from NE to SW respectively. The farm effect on the total water flux over a month through the Sec2 displays a semi-lunar periodic oscillation and is one order of magnitude smaller than that at Sec1. An asymmetry tidal current was observed in the farm north of Gouqi Island. The field observation of vertical profiles of current suggests that the thickness of surface canopy boundary layer can reach 5 m upstream from the farm during flood tide, increases gradually downstream up to 10 m under the cumulative influences of the farm. And a wake zone was observed downstream from the farm during flood tide. Better understanding of farm-induced hydrodynamic effects provides insight into how to optimize farm layouts based on local hydrodynamics, to maximize farm productivity and minimize environmental impacts.

Mussel Culture Activities Facilitate the Export and Burial of Particulate Organic Carbon

“…Hydrodynamic conditions are pivotal in influencing sediment resuspension. Field observation and numerical simulation revealed that the current velocities at the surface, middle, and bottom layers in the mussel farms decreased by 80%, 55%, and 45%, respectively, attributable to the presence of culture rafts and ropes [25,54]. Therefore, a mussel farm with stable hydrodynamic conditions inhibits the resuspension of surface sediments, leading to lower SPM levels and high organic matter preservation within the mussel farm.…”

“…Gouqi Island, located in the northeastern part of the islands in Zhoushan City, Zhejiang Province, China, is a typical region for shellfish mariculture. This island is at the heart of the Zhoushan Fishery, boasting a mussel farming area exceeding 12 km 2 and annual production of over 180,000 tons [25]. The dominant species, Mytilus coruscus, is cultivated using raft culture techniques that do not require additional feed.…”

Risk level assessment of typhoon-induced wave fields around a large-scale suspended mussel farm

“…Suspended longline form was adopted to culture mussels in Gouqi Island, which is consist of a buoy, mussel ropes, longline, mooring line and anchor block (Lin et al, 2016b;Zhong et al, 2022). Suspended culture can keep the shellfish on the surface of the ocean with plenty of natural food and protect it from predators (Mascorda Cabre et al, 2021).…”

“…Many scholars have conducted studies on the hydrodynamic characteristics of the suspended aquaculture farm. Field observations and large-scale numerical simulations have previously demonstrated that aquaculture farms can influence tidal flow at the scale of bays and the open ocean (Stevens et al, 2007;Plew, 2011a, b;Lin et al, 2016b;Liu and Huguenard, 2020;Zhong et al, 2022). Suspended shellfish farms induce current reduction of surface water layer (He et al, 2022), generate turbulence (Stevens and Petersen, 2011) and increase water exchange time (Liu and Zhang, 2022).…”