Considering ecosystem modeling by examining the creation of microcosms for Daphnia coexistence using an inorganic medium

Abstract To conserve natural ecosystems, we require suitable experimental methods with which to investigate them. Ecosystem models, called microcosms, have the potential to predict and improve our understanding of the phenomena in natural ecosystems. However, it is known that there are discrepancies between microcosms and natural ecosystems, such as different phosphorus circulation depending on the scale of the microcosm. Therefore, it is necessary to understand why the differences appear and to consider the coexistence of species, the medium composition, and the internal structure of microcosms in order to reproduce more of the phenomena that occur in natural ecosystems. To address this, in this investigation a microcosm (DMC) was constructed in which a variety of organisms could coexist by circulating the necessary nutrients which had been biosynthesized from essential elements (31 elements) inserted into the medium as inorganic substances. The growth of Daphnia, which requires vitamins (B12, B1, B7), was then observed by changing the sediment inside the microcosm with the inorganic medium containing all the essential elements. Using quartz sand with a particle size of 0.3–0.6 mm as the sediment, resulted in the stable growth of Daphnia, from 3 to approximately 26 individuals over 35 days, due to the growth of algae such as diatoms, which are feed for Daphnia. This suggests that 0.5 mm particle spaces are suitable for anaerobic bacteria, and that the nutrients necessary for the organisms, such as vitamins, were biosynthesized from the essential elements in the space. These results indicate that the DMC, which can duplicate the cycles that occur in natural ecosystems, such as the production of nutrients from inorganic substances, and the diversification of organisms in the microcosm, will be a useful tool for understanding natural ecosystems and factors that impact them, such as the effects of chemicals.