Development of integrated aquaculture in Sanriku coastal waters based on evaluation of environmental carrying capacity

为建立三陆海域海藻贝类可持续综合养殖模式，对大口湾进行了环境承载力调查。采用物理-生态耦合三维模型对扇贝的摄食生态、养殖筏下的氧气分布、物质循环进行了数值分析。在实验室和自然条件下，扇贝都能有效地利用微型浮游动物和桡足类以及浮游植物。扇贝作为浮游动物与浮游植物的竞争对手和超浮游生物的间接消费者，其生态重要性得到了证实。通过对河流入流产生的盐度分层进行精细处理，大大提高了物理模型流场的再现性。将该耦合模型应用于牡蛎和扇贝的生长。随着养殖密度的增加，这两种贝类的生长都变慢了，这表明密度对食物供应有影响。这种趋势在牡蛎中比在扇贝中更为明显。在目前的做法下，湾内贝类的密度可能符合环境承载能力。超过这个密度，贝类的生长减少很多，但低于这个密度，生长不增强。海湾中部的扇贝比内部生长得更快，这是因为由于活跃的水流有利于向养殖筏供应食物，中部的食物供应更好。因此，通过将文化区转移到海湾的中部地区，可以预期更高的产量。

In order to establish sustainable, integrated aquaculture of seaweeds and shellfish in Sanriku coastal waters, environmental carrying capacity of Otsuchi Bay was investigated. The research activities were focused on feeding ecology of the scallop Patinopecten yessoensis, oxygen distribution under culture rafts, and numerical analysis of material cycling using a physical-ecological coupled three dimensional model.The scallop efficiently utilized microzooplankton and copepods as well as phytoplankton under both laboratory and natural conditions. Ecological importance of the scallop was confirmed as a competitor of zooplankton for phytoplankton and an indirect consumer of ultraplankton, which were not fed directly, but through microzooplankton grazing.Reproducibility was much improved in flow field of the physical model by the refinement of salinity stratification which was produced by riverine inflow. The coupled model was applied to growth of oysters and scallops. Both shellfish grow slower with an increase of their culture density, indicating a density effect on food availability. This tendency is more distinct in oysters than scallops.The density of the shellfish at the current practice in the bay likely meets environmental carrying capacity. Beyond this density, growth of the shellfish reduces much, but below this, growth is not enhanced. Higher growth of scallops is obtained in the central part of the bay than the inner part This is explained by better availability of foods in the central part due to active water flow that facilitates food supply to culture rafts. Thus, higher production can be expected by shift of culture areas to the central part of the bay.