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

为了在三陆近海沃茨建立可持续的海藻和贝类综合养殖，对大槌湾的环境承载力进行了调查。本研究主要围绕虾夷扇贝的摄食生态学、养殖筏下的氧分布以及物理-生态耦合的三维物质循环模型进行了研究，在实验室和自然条件下，虾夷扇贝对小型浮游动物、桡足类和浮游植物的有效利用。扇贝的生态重要性被证实是浮游动物对浮游植物的竞争者和超级浮游动物的间接消费者，它们不是直接进食，而是通过微型浮游动物的摄食。将耦合模型应用于牡蛎和扇贝的生长。随着养殖密度的增加，这两种贝类的生长速度都变慢，表明密度对食物供应的影响。这种趋势在牡蛎中比扇贝更明显。海湾目前的贝类密度可能符合环境承载力。超过这个密度，贝类的生长会减少很多，但低于这个密度，生长不会增强。海湾中部扇贝的生长速度比内部更快，这是由于活跃的水流有利于向养殖筏提供食物，因此中部食物的可用性更好。因此，更高的生产可以预期的文化区转移到海湾的中部。

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.