The growth processes of the coral assemblages were analyzed using the data of an 8-year study on the coral communities in Naha Port, Okinawa Prefecture, Japan. The data was collected from the coral assemblages distributed on a breakwater at various water depths in the port. It was analyzed using multiple regression and neural network analysis to determine the relationship between the coral growth and the environmental factors. Sensitivity analysis was also conducted to estimate the weight of the environmental factors on the growth of the coral communities. The annual growth rate of coral assemblages evaluated as the change in coral cover showed increase in 6.3 %y^-1 at the depth of 1 m, 4.9 %y^-1 at 3 m, but only 2.5 %y^-1 or less from the depths of 5 m to 12 m. Multiple regression analysis was carried out for the examination of the effects of environmental factors on the coral growth and the result showed that four factors including underwater solar radiation, substrate gradient, current speed on substrates, and the previous coral cover were important factors in determining the coral coverage of the following year. The accuracy of the prediction both for multiple regression analysis and neural network analysis showed a significant accuracy of R²=0.80, n=72, P<0.001, and R²=0.83, n=72, P<0.001, respectively. In the sensitivity analysis using the neural network model, an increase in underwater solar radiation, current speed on substrates and coral cover in the previous year led to a larger coral coverage in the following year, whereas an increased gradient resulted in a smaller coverage.

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Photosynthetic bioreactors using microalgae have been used in the past and are effective in biological oxygen regeneration in the CELSS. However, there is little published data on the utilization of algal biomass. In order to utilize it as food for zooplankton using a Closed Ecological Recirculating Aquaculture System (CERAS), this study examined the optimal food concentration and the algal biomass conversion efficiencies based on dry weight in different feeding levels for water fleas, Moina macrocopa, fed on Chlorella algae, Chlorella vulgaris. In experiment 1, M. macrocopa were cultured for 3 days under five different food concentrations (10^5.0, 10^5.5, 10^6.0, 10^6.5 and 10^7.0 cells/mL) in aerated 2L beakers. Growth rates of M. macrocopa increased with higher concentration of microalgae up to a concentration of 10^6.0 cells/mL. Increasing the concentration above 10^6.5 cells/mL resulted in lower growth rate. The result shows that the growth of M. macrocopa is impeded at the concentration above 10^6.5 cells/mL. In experiment 2, M. macrocopa were fed at a rate of 4 × 10⁵ cells/individual for 1^st day with concentration of cells feed increasing at rates of 1.2, 1.4 and 1.6 times/day up to day 5. The biomass conversion efficiency for the treatments were 0.308 ± 0.039, 0.306 ± 0.015 and 0.287 ± 0.020/day respectively, and the values were not significantly different (p>0.05). The results show that biomass conversion is similar between the different feeding rates. Thus, the population growth of M. macrocopa depends on feeding level and can be controlled by feeding, without changing biomass conversion efficiency.

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Closed Ecology Experiment Facilities (CEEF), an experimental “mini-earth,” is composed of several closed chambers physically separated and sealed from outside except the flows of energy and information. CEEF was designed to house plant, animal, and human ecosystems in the separate chambers and to maintain a constant environment needed to sustain all living organisms in these chambers by circulating CO₂, O₂, water and other necessary elements for living organisms between chambers. Therefore the overall ecosystem planned in CEEF makes it scientifically a mini-earth model. The behavior of ¹⁴CO₂ released from nuclear reprocessing sites into the natural environment can be simulated by tracking ¹⁴C dynamics in the artificial mini-earth. In the nuclear power generation process, ¹⁴C is produced from ¹³C, ¹⁴N, ¹⁵N, ¹⁶O, and ¹⁷O atoms by neutron collision and radioactive decay. Oxygen atoms in uranium oxides and nitrogen atoms contained in the binder used for solidifying fuel rods are changed to ¹⁴C, and ¹⁴CO₂ is also produced during reprocessing and is released. In the natural environment, percentages of carbon isotopes are ¹²C: 98.892%, ¹³C: 1.108% and ¹⁴C: 0.05%. The decay constant (half life) of ¹⁴C radioactive material is about 5570 years. Therefore it is inadvisable to put ¹⁴C in the habitat of CEEF, so instead, the stable isotope ¹³C is used to simulate the accumulation quantities of ¹⁴C in each ecosystem and atmosphere of CEEF. The ability of plant leaves to take in CO₂ seems to change a little because of the mass difference of ¹⁴C and ¹³C carbon isotopes. This discrimination ratio between ¹⁴C and ¹³C can be measured using the radioisotope laboratory facility located near CEEF. The quantity of ¹⁴C taken in by plants is estimated using this discrimination ratio. On the other hand, animals and human eat foods coming from plant biomasses and digest them without any discrimination. And the stored carbon in their bodies can be estimated by analyzing the foods, expiratory gases, and feces and urine excreted. In order to proceed with this radioactive trace experiment, it is necessary to establish the complete circulation system of metabolic materials produced from living organisms including human being. The habitation experiment is on the way to this target and its schedule is presented.

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