In summer of 1997, submerged macrophytes were investigated in 6, 354 quadrats (10 m × 2 m) along 104 transects covering the whole littoral zone of Lake Biwa by SCUBA diving to obtain a quantitative view of species composition and horizontal and vertical distributions of respective species. Twenty three species were found in this survey. The species with a high frequency were Potamogeton maackianus, Hydrilla verticillata and Elodea nuttallii. The vegetation was classified into four types by cluster analysis using values of similarity index among all transects. Four types were as follows: west and north (N1), north-east (N2), south-east (N3) in Northern Basin, and Southern Basin (S). N2 type had the largest vegetational cover, cover layer, number of species and diversity index, and N1 type the smallest number of species. Applying the principal component analysis for Northern and Southern Basins, the richness of vegetation could be reasonably ordinated by the first principal component. The groups of species growing in different environmental conditions (wave energy, water depth, transparency and grain size) were also interpreted by the second and third principal components.
Scatter diagrams for water depth and grain size of submerged macrophyte species showed the characteristic of habitat conditions in each basin, indicating higher habitat diversity in Northern Basin than in Southern Basin. Differences in vertical distubution patterns of some species between the basins were discussed in relation to the growth form, interspecific competition and environmental change (eutrophication, etc.). Influence of water level fluctuation on submerged macrophyte species was also discussed in the context of a possible low-water level (B.S.L. -1.5 m) in the Lake Biwa Development Project.

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Upstream migration in the Japanese mitten crab Eriocheir japonica was investigated in the lower region of the Saigo River and the adjacent seas in Fukuoka Prefecture, Japan. Megalopa larvae settled and metamorphosed to the crab stage in the upper tidal area in the river. The youngest crabs were nearly 2 mm in carapace width (CW). After attaining a minimum of 3.6 mm CW, the crabs began to migrate upstream and reached the freshwater area. Settlement of megalopa larvae occurred mainly in mid autumn (October) and late spring (May to June), while small numbers also settled in November and January - February. However, the majority of larvae that settled in winter did not survive and metamorphose to the crab stage due to low water temperatures (< 10°C). The young crabs that metamorphosed in autumn and winter remained in the tidal area and did not grow throughout winter. Upstream migration of the autumn settlers to the freshwater area was observed from March until June. They started to grow in March, and reached nearly 10 mm CW by June (about 8 - 9 months after settlement). In contrast, the larvae that settled in May to June grew very fast, reaching nearly 10 mm CW in September (about 4 months after settlement). Their upstream migration to the freshwater area began in July and ended by August. Thus, the growth and upstream migration of E. japonica seemed to be strongly influenced by water temperature in the estuary. This mode of settlement with two peaks in autumn and early summer reflected the temporal pattern of reproduction observed in the sea. With respect to engineering works in river estuaries and the release of the crab to rivers, it is recommended that we take into account the processes of settlement and migration of young crabs. We may also require information on the migratory processes of other diadromous crustaceans for their effective conservation and management.

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Occurrence of high algal growth above the rivermouth barrage in the Nagara River was examined during the high flow rate in the river was decreasing, by using the data of the Japanese Ministry of Construction River Bureau and the Water Resource Development Public Corporation. Recent researches in the Nagara River showed that after closing the gate the high algal growth was generally observed above the rivermouth barrage when a low flow rate continued having enough solar radiation, because the river water contains enough nitrogen and phosphorus as the nutrients. However, Murakami et al. (1998) found that when the low flow rate continued a rather long time, the amount of algae decreased probably because of the sedimentation of algae near the gate and the feeding by rotifer. Results of this study based on the continuously recorded data at a station above the barrage showed that high algal growth could be found when the flow rate decreased to the level ranging from 100 to 60 m³ sec^-1. This range of flow rate almost agree with those suggested by Murakami et al.(1998) to maintain a high algal growth.

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