Development of stable-isotope studies in production ecology of bivalvia.

双壳类是封闭海湾的主要渔业资源，但在其生产生态中有许多模糊之处。利用天然碳、氮稳定同位素丰度比分析了哈马纳-科湾牡蛎的生产机理，并对该技术的应用前景和存在的问题进行了探讨。哈马纳-科湾口区颗粒有机质主要由碎屑组成，L3δC<-21。在内区，当观察到水华时，牡蛎甘纳达尔消化部(GD)的13δC和15δN与POM的变化是同步的，但POM和13δC的状态与口区相同，没有发生特定的水华。通过对微体和中体藻类POM的培养实验，发现藻类POM的稳定同位素比值除了受藻类种类的影响外，还受藻类的营养类型、光合作用、生长阶段等因素的影响。此外，对牡蛎代谢状态的影响实验表明，无论是成熟、升温还是生长，都会使牡蛎的同位素周转变得迟钝。总之，对作为牡蛎主要食物来源的碎屑的定量研究将比初级生产力更重要。天然13δC和15δN的稳定同位素比值是在藻类POM或牡蛎养殖实验中指出波动因素后的有效工具。

Bivalves have many obscurity In their production ecology, though they are majour fishiery resorces of a closed bay. We analysed production mechanism of the oyster Crassostrea gigas in Hamana-ko bay using natural abundance ratios of C and N stable isotopes, in addition to the discussion on the prospects and problems of the technic.In a mouth area of Hamana-ko bay, particulated organic matter (POM) was mainly composed of detritus, and l3δC was lower than -21. In inner areas, both 13δC and 15δN of a ganadal-digestional part (GD) of the oyster changed synchronously with those of POM when algal bloom was observed, but the satates of both POM and 13δC were the same as in a mouth area when any particular blooming didn't occur. We made clear that oyster production in the lake depends on detrirus fundamentally and additional growth are supported by primary production.From culturing experiments on algal POM both in microcosms and mesocosms, stable isotope ratios of POM were revealed to be affected either with nutritiona1 type, photo-synthesis activity or growth phase of algae, in addition to algal species.Another culturing experiments on the effects of metabolic states of the oyster showed that either maturation, increasing temperature or growth makes the turnover of isotopes dull.In conclusion, quantitative investigations on detritus would be more inportant than on primary production which was thought to be main food source of the oyster. And, stable isotope ratios of natural 13δC and 15δN will be "effective tools" after fluctuation factors pointed out in culturing experiments on algal POM or the oyster.