Mitigating the impacts of oligotrophication and thermal stress on Pacific oyster Magallana gigas aquaculture through solar-powered artificial upwelling

Abstract Recent oligotrophication and rising water temperatures in the Seto Inland Sea of Japan have led to a decline in oyster production in Hiroshima Prefecture. This study developed and evaluated the “Seawater Pump-up Apparatus for Localized Oceanic Warming-mitigation” (SPALOW), a device designed to supply cool and nutrient-rich bottom water and diatom resting cells from the sediment to the surface layer. Field trials conducted in Mitsu Bay, Hiroshima in 2023 revealed that the experimental raft equipped with SPALOW exhibited lower surface water temperatures during summer and increased dissolved inorganic nitrogen (DIN) concentrations. Chlorophyll- a concentrations were consistently higher throughout the year, resulting in a 32.7–75.6% increase in the wet weight of oyster soft body compared with the control raft. By simultaneously enhancing phytoplankton availability and mitigating thermal stress, SPALOW represents a promising tool for establishing sustainable and efficient oyster aquaculture systems in the future.