Feasibility of a passive tidal floating upweller system for the nursery culture of bivalve spat

High losses of juvenile bivalves, such as oysters, clams, and mussels, during nursery culture reduce the overall efficiency of aquaculture production of many species. These losses can be mitigated through effective contained nursery culture systems, which provide sufficient flow of water containing suspended food particles to facilitate the growth of juveniles, usually in an upwelling arrangement. Raw seawater can be used to provision upwelling nursery systems with flowing water containing particulate food, but it requires substantial energy input to pump large volumes. This study sought to eliminate the energy inputs for nursery culture by conducting a feasibility study on a tidally driven floating upweller system (FLUPSY) using a comprehensive simulation and experimental study approach. A passive tidal FLUPSY was designed based on established designs, followed by comprehensive computational fluid dynamics simulations in flume and ocean fluid domains. The results from laboratory flow visualisation experiments showed good agreement with the simulations. Field experiments further validated the simulation results, and the observed flow velocities mirrored those obtained from simulations. However, the results of both the simulations and experiments revealed that despite an upward trend along the inclined intake ramp, the flow near the spat location in the passive tidal FLUPSY was relatively low. As such, an optimisation study was carried out to increase the FLUPSY's outlet velocity, which showed that a three times increase in inlet area resulted in 62 % of the incoming tidal flow being conveyed through the passive tidal FLUPSY. Nevertheless, the disproportion between the FLUPSY's inlet and outlet areas presents challenges to commercial viability. These results provide valuable insight into the feasibility of a passive tidal FLUPSY for bivalve aquaculture and underscore the need to further explore alternative active tidal FLUPSY designs to address these limitations.