To evaluate the dietary effect of heterotrophic flagellates on production of cladocerans, we assessed survival, somatic growth and reproduction of Daphnia pulicaria fed heterotrophic flagellate Kinetoplastid. In addition, for comparison to Kinetoplastid, bacteria and Chlorella vulgaris were used as food sources for D. pulicaria. In the food treatment with Kinetoplastid, D. pulicaria did not mature and died within 8 days. The same result was found in the treatment with pure bacterial diet （bacteria 100%）. To compare the somatic growth of D. pulicaria among the food treatments, we calculated increment rate （mm ind.－1 day－1） of body length of D. pulicaria from 0 age （day） to maturation or death （the treatments other than pure Chlorella diet, Chlorella 100%）. The increment rate （mm ind.－1 day－1） was low in the food treatments with Kinetoplastid as compared with that in the pure Chlorella diet. Our findings have suggested that Kinetoplastid are not necessarily sufficient food source for production of D. pulicaria. The results might be valuable in plankton ecology because information about dietary effect of heterotrophic flagellates on cladocerans has been lacking. The present study indicates that it might be necessary to consider what kind of cladocerans are useful for target reservoirs of biomanipulation to improve water transparency because the genus Daphnia, which is often used in biomanipulation, sometimes decline in the environments with abundant microbial diets （bacteria and heterotrophic flagellates）.
This study focused on the effect of leaf litter of different tree species on the water quality of ponds. Differences in the effects of substances eluted from dry leaves from a broad-leaved deciduous tree （Kunugi, Quercus acutissima） and an evergreen coniferous tree （Japanese cedar, Cryptomeria japonica） were examined using four outdoor experimental ponds. Each pond shape has a length 2.5 m, width 2.5 m and depth 1.0 m. Dry leaves were added to three of the ponds in ratios of 100% Kunugi, 100% Japanese cedar, and 50% of each species. The fourth pond was used as a control pond. The concentrations of CODMn, TP, TN, and potassium ions due to water－soluble substances from the dry Kunugi leaves were higher than those from Japanese cedar leaves; the elution rate was also faster for Kunugi leaves. Additionally, the concentration of chlorophyll-a （an indicator of phytoplankton） was greater in the “Kunugi pond” than in the “Japanese cedar pond.” Therefore, the influence of dry Kunugi leaves on water quality was greater than that of Japanese cedar leaves. However, dissolved oxygen, which is important in habitats for aquatic organisms, was observed in poor oxygen （dissolved oxygen: ＜2mg・L－1） inappropriate habitats in ponds treated with both Kunugi and Japanese cedar leaves, and these conditions continued for more than one week. In managing the water quality of ponds, it is possible to reduce the amount of elution by immediately removing fallen leaves from the water.
This study focused on the effect of temperature on biological removal of petroleum hydrocarbons. Seawater samples were collected from two stations in Tokyo Bay seasonally, and were made into petroleum-polluted seawater by adding mixture of n－alkanes in a fixed concentration in laboratory. A 28 days of bioremediation incubation experiment was carried out with and without additional nutrients supplement in each season, and the remained hydrocarbons during incubations were measured by GC－MS. alkB gene, the functional gene responsible for alkane degradation, was also recorded throughout the incubation. Our results showed that bioremediation efficiency of petroleum hydrocarbon was highest in summer, followed by spring, autumn, and winter respectively. Alkanes with as much as 34 carbon atoms can be significantly degraded within 28 days of incubation in summer, and in contrast, no obvious degradation can be recognized in winter regardless of the number of carbon atoms. N－alkanes degradation efficiency was generally associated with, but not necessarily correlated to the copy number of alkB gene.