To evaluate the physicochemical environment（nutrients and light）at high and low tide in the inner western part of Ariake Bay during winter, observations were made from estuarine to offshore areas. Diatom blooms, dominated by the genus Skeletonema, and low dissolved inorganic nitrogen（DIN）concentrations were observed in the offshore area on December 5, 2017. As a result of the diatom blooms, DIN concentrations in the estuary at high tide on December26, 2017were low, except in the upper estuary. Although DIN concentrations in the upper estuary were high, euphotic depth to water depth ratios（zeu/z） were low（＜0．6）due to high turbidity. Tidal movement of the water mass from the upper estuary to the offshore area resulted in high-nutrient areas offshore during low tide on December 27, 2017, and zeu/z increased due to the decreased depth. This suggests that the light environment of a water mass with high nutrient concentrations improves from high tide to low tide, benefiting diatom growth, which may influence diatom population growth in this area.

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The Fisheries Research Center, Ehime Research Institute of Agriculture, Forestry and Fisheries, has 28 fixed observation points in the Bungo Channel and conducts hydrographic observation at these points every month. Current data observed by a ship-mounted ADCP（acoustic Doppler current profiler）are recorded at these points. The ADCP data have limited application because instantaneous current data indicate the tidal current component in the Bungo Channel where the tidal current is dominant. If the tidal current can be eliminated from the instantaneous ADCP data, the residual current distribution in the Bungo Channel can be clarified, which will aid in understanding physical phenomena. In the present study, we examined how accurately the tidal current can be estimated from monthly ADCP data for 27 years using quasi-observed data made from numerical model outputs. The accuracy of tidal current estimation in the southern part of the Bungo Channel was low because of a smaller tidal current and larger residual current. On the other hand, we were able to estimate8tidal constituents with a total error of1cm s－1－3cm s－1 in the middle and northern parts of the Bungo Channel. We averaged27years of residual currents at depths of10m and50m in January, April, July, and October, which were derived from de-tide ADCP data of the Fisheries Research Center in Ehime. Seasonal variation in residual current patterns in the Bungo Channel is not large because tide-induced residual currents are dominant.

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Nomi Bay in Susaki, Kochi Prefecture, has experienced numerous earthquakes in the past. The oral tradition of Kurodagori, a coastal village submerged under seawater due to the Hakuho Earthquake in684AD, is well known in this area. Since no scientific evidence of Kuroda-gori has been presented to date, a seafloor survey of Nomi Bay was undertaken to locate the footprint of the submerged village. The results revealed the existence of a plateau at a depth of6m to7m measuring 0．09km2 that sloped gently toward deeper water in the northeastern part of Heshima Island. The site was previously reported to contain the ruins of a freshwater well. The seafloor in the platform was mainly covered with a thin sand layer, with the amount of gravelly substrates increasing toward the shore. The sand layer is considered to overlie hard basement rocks. These topographic and geological features are consistent with a wave-cut platform. Based on relative sea level changes and vertical coseismic movements, the former platform was probably submerged by the Nankai earthquake. This submarine platform may have been

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有明海における環境問題・漁業問題が全国的に知られるようになって20年になる．しかし，二枚貝類（タイラギ・サル ボウ・アサリ等）の漁獲量減少，マクロベントスの減少，貧酸素水塊の発生，赤潮の発生など，様々な問題が起きている にもかかわらず未だに原因は不明な点が多く，根本的対策は見つかっていない．本稿では有明海における環境問題・漁業 問題を概観し，潮汐・潮流，貧酸素，赤潮，漁獲量等，長期的な環境変化に関する研究をレビューする．その上で，最後 に今後の再生方策について論じる．

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When large-scale constructions or big projects are planned in a coastal region, environmental assessment that includes predictions with numerical experiments is performed. Scientific understanding of phenomena in the coastal ocean is frequently based on numerical experiments. Their reliability depends on their reproducibility with the observed evidences ; however, quantitative evaluation is insufficient. Herein, we discuss the reproducibility of tidal currents that were analyzed with numerical models. At first, temporal variations in the tidal harmonic constants that were calculated with a time series of current velocity observed at fixed stations revealed the uncertainty of the harmonic constants that are analyzed in typical environmental assessments. In the observations, the uncertainty of the M2 tidal current was about 10%. The harmonic constants were calculated with the results from four numerical models. Even for the cases with models that were reproducible, we found a10－ 20% difference of the M2 amplitude between the models. In the actual numerical experiments, performance of the numerical models could be often tuned with observation data. However, since it would be not easy to be tuned exactly everywhere in the domain, we recommend that a difference within20% from the observations should be allowed in numerical experiments.

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Using the concept of “yutakasa”（rich in everything）with the definition and measurement of affluence or bountifulness based on related papers, we analyze environmental and fisheries administrations in Japan and contrast them with the concept of ecosystem services in conservation ecology.

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Following the previous contribution, we examine the complicated interactions of sea stakeholders such as the evaluation and the measurement of the sea as related to marine ecosystems, social position of fisheries, and“satoumi”.

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