Abstract A measured reduction in the phosphorus load in Hiroshima Bay, Japan, is suspected to be the root cause of the declining success of oyster spat collections and rates of oyster production over the past 30 years. The lack of phosphorus leads to an inadequate abundance of phytoplankton as food sources which, along with competition among various filter feeders, might have generated the poor culture conditions. To understand how prey-predator interactions, including those of cultured oysters, are functioning, we developed a prey-predator model. Phytoplankton in different size categories were quantified, with a particular focus on phytoplankton smaller than 5 μm, which represent suitable food sources for oyster larvae during the planktonic phase. Filter feeding animals that compete with oysters were also identified and counted. Our numerical model consisted of 25 compartments, including inorganic/organic substances, phytoplankton, zooplankton, oysters, other filter feeding animals, and fish. The model outputs reproduced the observed temporal variation of the various parameters well, including the different size categories of oyster larvae from just spawning to settlement. Sensitivity analyses showed that an increase in the dissolved inorganic phosphorus load to 10 times than present value (0.2 mg P m−3 d−1) enhanced phytoplankton production, including that of small-sized phytoplankton, facilitating an increase of 51% in the successful settlement of oyster spat. In conclusion, the recent low success rates in the settlement of oyster larvae appear to be driven by insufficient quantities of the phytoplankton on which they feed. This lack of phytoplankton stems mainly from the reduction in the nutrient load in addition to competition between oysters and various other filter feeders for these food resources.

中文翻译：

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日本广岛湾牡蛎幼虫低繁殖成功率的自下而上和自上而下控制建模

摘要 日本广岛湾磷负荷的测量减少被怀疑是过去 30 年牡蛎卵收集成功率和牡蛎产量下降的根本原因。磷的缺乏导致浮游植物作为食物来源的丰度不足，再加上各种滤食性动物之间的竞争，可能导致养殖条件差。为了了解包括养殖牡蛎在内的猎物-捕食者相互作用是如何运作的，我们开发了一个猎物-捕食者模型。对不同大小类别的浮游植物进行了量化，特别关注小于 5 μm 的浮游植物，它们代表了浮游阶段牡蛎幼虫的合适食物来源。与牡蛎竞争的滤食动物也被鉴定和计数。我们的数值模型由 25 个隔室组成，包括无机/有机物质、浮游植物、浮游动物、牡蛎、其他滤食动物和鱼类。模型输出很好地再现了观察到的各种参数的时间变化，包括从刚产卵到定居的不同大小类别的牡蛎幼虫。敏感性分析表明，溶解无机磷负荷增加至当前值（0.2 mg P m-3 d-1）的 10 倍可提高浮游植物的产量，包括小型浮游植物的产量，促进成功增加 51%。牡蛎卵的解决。总之，最近牡蛎幼虫定居的低成功率似乎是由于它们赖以生存的浮游植物数量不足所致。