Increases in water temperature due to climate change are expected to lead to cyanobacterial blooms in various freshwater bodies, including reservoirs, posing a major challenge in terms of water quality management. Therefore, a detailed understanding of the dynamics of cyanobacteria in water bodies is required to increase our knowledge of cyanobacteria. In this study, we attempted to determine the spatial distribution of cyanobacteria in a water body by acoustic techniques, and to understand the distribution of cyanobacteria and how it is affected by the water environment. At the same time, the validity of acoustic measurements of cyanobacteria was verified. Comparison of the estimated abundance of cyanobacteria by acoustic measurements and the measured pigment values of cyanobacteria showed a positive correlation between them, suggesting that acoustic measurements of cyanobacteria are effective. The field survey provided us with a large number of data and allowed us to map the spatial distribution of cyanobacteria in the water body. The results suggest that cyanobacteria are propagated or transported by the water quality control facilities of the reservoir and the water environment. In particular, unlike natural environments, reservoirs are expected to undergo severe environmental changes due to artificial facilities such as water quality control measures, and it will be important to continue monitoring cyanobacteria on a detailed scale using acoustic techniques. Continued research in this area is anticipated to lead to more effective strategies for managing water bodies and mitigating cyanobacterial blooms.

Periodic monitoring can provide important information for the protection of endangered fish, sustainable use of fishery resources and management of alien species. Previous studies have attempted to monitor fish using non-invasive environmental DNA (eDNA) technology, generally employing quantitative PCR to quantify the eDNA concentration. However, the throughput was limited. High-throughput metabarcoding technology can detect the DNA of multiple species simultaneously in a single experiment but does not provide sufficient quantification. In this study, we applied a quantitative metabarcoding approach to simultaneously quantify the eDNA concentration of an entire fish assemblage in a small reservoir over two summer seasons. Traditional surveys were also conducted to investigate the individuals of fish. The eDNA concentrations were quantified using quantitative metabarcoding, and the fish species detected using this approach were highly consistent with the results of traditional fish monitoring. A significant positive relationship was observed between the eDNA concentration and fish species abundance. Seasonal changes in fish community structure were estimated using eDNA concentrations, which may reveal the activity seasons of different fish. The eDNA concentrations of different fish species peaked at different water temperatures, reflecting the differential responses of fish species to this environmental factor. Finally, by detecting outlier eDNA concentrations, the spawning activities of 13 fish species were estimated, 12 of which were roughly consistent with the current knowledge of fish spawning periods. These results indicate that quantitative eDNA metabarcoding with dozens of sampling times is useful for the simultaneous ecological monitoring of multiple fish species.

During spawning activity, fish release large amounts of sperm and eggs into the water, which has been assumed to cause an increase in environmental DNA (eDNA) levels and nuclear DNA/mitochondrial DNA ratios. To test whether these assumptions are valid and whether nuclear and mitochondrial eDNA analysis can be used to monitor the spawning activity of freshwater fish, we conducted field eDNA surveys and traditional surveys using common carp (Cyprinus carpio), largemouth bass (Micropterus salmoides) and bluegill sunfish (Lepomis macrochirus) as model species. Fish spawning periods were estimated based on age, as estimated using the body lengths of juveniles collected in the Miharu reservoir in Fukushima, Japan. The results showed that the main spawning periods of largemouth bass and bluegill sunfish were from April to July and from July to August, respectively. Field eDNA surveys were conducted in the Hebisawagawa front reservoir, which is connected to the Miharu reservoir. From March to August 2019 and 2020, weekly eDNA sampling was conducted at three sites, and daily sampling was conducted at six sites from 23 June to 3 July 2020. The eDNA concentrations of the nuclear internal transcribed spacer 1 (ITS1) and mitochondrial cytochrome B (CytB), as well as the ITS1/CytB ratio, were measured for each of the three fish in each water sample. Water temperature had a statistically significant effect on eDNA concentration, probably reflecting the relationship between water temperature and spawning. We created generalised additive mixed models to estimate spawning activity periods based on weekly eDNA data. The estimated periods of spawning activity for common carp, largemouth bass and bluegill sunfish were March to May, May to July, and May to August, respectively. The estimated spawning periods coincided with known fish ecology or the results of traditional methods. This method also has been applied to daily eDNA samples, showing the feasibility of high-resolution estimation of spawning activity. For common carp and bluegill sunfish, we were able to estimate the spawning period using this method. Although the method is affected by biomass and the diffusion and degradation of eDNA, it has the potential to accurately estimating spawning activities. These then can be estimated without conducting laborious traditional surveys, facilitating the monitoring of reproduction by rare, invasive or important fishery species. Further research on the diffusion distance and degradation time of the eDNA concentration peak caused by fish spawning activity may improve the accuracy of monitoring.

仙台湾南部海岸の深沼地区では，東日本大震災後の海岸堤防の復旧工事において，海岸堤防の法線を堤内地側へ移動する（セットバック）を含む環境保全対策が行われた．応用生態工学会仙台では，砂浜生態系および生物群集に対する環境保全対策の効果を評価するために，2018 年度（平成 30 年度）に「仙台海岸環境モニタリングプロジェクト」を立ち上げ，2019 年度（令和元年度）から深沼地区における砂浜生態系の状況の追跡調査を開始した．2019 年は 8 月に，物理環境調査，植物調査（コドラート調査，注目種調査），陸上昆虫類等（昆虫類以外の節足動物も含む）調査を実施した．調査の結果，生物（植物および陸上昆虫類等）の生息・生育要因については汀線からの距離，地盤高との関係性を確認した．また，環境保全対策の一つとして堤防のセットバックを実施した A エリア（海浜性生物の回復が顕著で，物理環境面から海浜性生物にとって潜在的に良好な生息域）では，堤防工事から 10 年経過した現在も，海浜性生物にとって潜在的に良好な生息域が維持されていることが明らかとなった．一方で，再生の核と位置付けた A エリアからの生物の広がりを期待した C エリアは，A エリアほどの潜在的に良好な生息域には至っていなかった．応用生態工学会仙台では 2020 年度以降も毎年，追跡調査を実施している．今後は，海岸堤防が植物の種子の移動分散や陸上昆虫類等の徘徊，飛翔に及ぼす影響，飛砂や波浪に及ぼす影響をより詳細に調査し，堤内地に影響が及ぶメカニズムの解明を進めたい．

Abstract Dam‐mediated biological invasions are a serious problem all over the world. Once established in reservoirs, the invasive species have catastrophic impacts on the river ecosystems downstream, and thus, rapid monitoring of invasive species is an urgent issue for the effective removal of them and the conservation management of native ecosystems. Here, we verified the utility of environmental DNA (eDNA) analysis as a tool to effectively monitor three invasive fish species (bluegill, largemouth bass, and smallmouth bass) in reservoirs using multiplex real‐time PCR. First, to determine the optimal sampling location and season to detect eDNA from these species, we analyzed the eDNA in water samples from shore and offshore sites in three reservoirs all year around. We found that eDNA detection rates either did not differ between sampling locations or were higher for shore than offshore sites. In addition, eDNA detection rates were higher in spring (breeding season of target species) and/or summer than winter. Second, we extensively surveyed the distribution of the three species in 30 reservoirs in Japan using eDNA analysis. Consequently, a single eDNA‐based surveillance in summer allowed to match approximately 90% of the presence/absence of the invasive fish species known from 27 yr of administrative capture‐based surveillances. Given these results, we recommend collecting the replicated water samples from shore sites in summer or the breeding season for the effective detection of invasive fish eDNA in reservoirs. Our eDNA assays with multiplex real‐time PCR enable the rapid and sensitive monitoring of invasive fish distribution in reservoirs.

Abstract Environmental DNA (eDNA) analysis has seen rapid development in the last decade, as a novel biodiversity monitoring method. Previous studies have evaluated optimal strategies, at several experimental steps of eDNA metabarcoding, for the simultaneous detection of fish species. However, optimal sampling strategies, especially the season and the location of water sampling, have not been evaluated thoroughly. To identify optimal sampling seasons and locations, we performed sampling monthly or at two‐monthly intervals throughout the year in three dam reservoirs. Water samples were collected from 15 and nine locations in the Miharu and Okawa dam reservoirs in Fukushima Prefecture, respectively, and five locations in the Sugo dam reservoir in Hyogo Prefecture, Japan. One liter of water was filtered with glass‐fiber filters, and eDNA was extracted. By performing MiFish metabarcoding, we successfully detected a total of 21, 24, and 22 fish species in Miharu, Okawa, and Sugo reservoirs, respectively. From these results, the eDNA metabarcoding method had a similar level of performance compared to conventional long‐term data. Furthermore, it was found to be effective in evaluating entire fish communities. The number of species detected by eDNA survey peaked in May in Miharu and Okawa reservoirs, and in March and June in Sugo reservoir, which corresponds with the breeding seasons of many of fish species inhabiting the reservoirs. In addition, the number of detected species was significantly higher in shore, compared to offshore samples in the Miharu reservoir, and a similar tendency was found in the other two reservoirs. Based on these results, we can conclude that the efficiency of species detection by eDNA metabarcoding could be maximized by collecting water from shore locations during the breeding seasons of the inhabiting fish. These results will contribute in the determination of sampling seasons and locations for fish fauna survey via eDNA metabarcoding, in the future.

In Japan, farm ponds retain water throughout the year while rice fields are continuously inundated for no more than 2 months, usually from spring to early summer. Although the zooplankton fauna in artificial water bodies would be expected to vary according to differences in inundation periods, scientific confirmation of this relation is largely lacking. Due to its ubiquity, the cladoceran Moina is a suitable target for studying habitat-related differences in the planktonic fauna, but its taxonomy remains unresolved, making morphological identifications potentially uncertain. We thus applied integrative taxonomy with both morphological and genetic evaluations for reliable species delimitation to Moina samples collected primarily in Japan (with smaller collections from Taiwan). This approach increased the alpha diversity of Moina species in Japan from three (in previous studies) to seven. It also revealed different habitat preferences among Moina species, with the smaller species being distributed mostly in farm ponds (followed by natural lakes), and the larger species mostly in rice fields. We argue that the phenological match/mismatch with inundation period of rice fields was a major factor for this strong trend of spatial species turnover, with differing degrees of fish predation pressure among the habitat types being another factor.

福島県阿武隈川水系三春ダムでは,制限水位方式のダム運用を行っており,通常,洪水期の開始直前に貯水位を低下させる.ちょうどこの時期は,外来魚の繁殖期と重複し,オオクチバスの産卵開始の目安とされる 15~16℃に表面水温が達する時期が含まれる.このため,ダム湖に特有の計画的な水位操作パターンに工夫を施し,外来魚の繁殖抑制を試みた.通常のダム操作は,貯水位を一定の割合で低下させていくが,三春ダムでは,途中で 2 ~ 4 日程度,水位を一定に保持してオオクチバスの産卵床形成を促進させ,その後,貯水位を低下させて産卵床を干出した.その結果,貯水位を一定に保った水深から 0.5 ~ 2 m 下に産卵床が多く観察され,段階式水位操作により,多くの産卵床を干出できることを確認した.繁殖に成功した稚魚を捕獲し,個体サイズ,耳石から産卵日を推定すると,水位低下中の繁殖成功は少ない結果となった.また,4 段式水位操作と 3 段式水位操作では,前者で繁殖成功数は少なく,より効率的に繁殖を抑制させる結果となった.個体群数の将来予測では,4 段式水位操作の場合,個体数は横ばいで,増加は抑制されると推定された.これらのことから,4 段式の水位操作により,貯水池内のオオクチバスの繁殖抑制は可能と考えられた.

三春ダムでは，河床礫に付着した古い付着藻類を定期的に更新することなどを目的に，2000 年から 10～20 m3/s のフラッシュ放流を実施している．本事例研究では，ダム下流河川の平瀬のデータから付着藻類の剥離に効果的なフラッシュ放流のタイミングを検討した． フラッシュ放流の付着藻類量に対する効果は，直前の付着藻類量によって異なり，クロロフィル a 量が15 μg/cm2 以上だった場合には効果があると考えられた．クロロフィル a 量が 15 μg/cm2 以上だったのは，10 m3/s 以上の出水が 7 日間以上無かった場合だった．したがって，フラッシュ放流予定日前の 7 日間の流況が安定している場合には，付着藻類量が多くなり，フラッシュ放流による剥離効果が大きいと考えられた．

北上川ダム統合管理事務所が管理する四十四田ダム，御所ダムおよび田瀬ダムで，1992 年から行っている計5 回の河川水辺の国勢調査に加え，2010-2014 年に電気ショッカー船による魚類調査を行った．

福島県阿武隈川水系大滝根川に建設された三春ダムでは, 貯水予定区域内にフクジュソウが自生しており, 冠水の影響を受けることが明らかであった. そのため, 冠水前に, 一部を自生地に残し, 残りを保全措置として冠水しない 4 地点に分けて移植した. 本研究では, 試験湛水前の 1996 年から 2009 年までの 14 年間, フクジュソウの個体群を追跡した. 自生地では試験湛水後, 個体数は増加傾向にあり, 開花個体 (F), 結実個体, 芽生え (S), 幼植物 (J1～J4) も存在していた. 移植地 4 地点のうち造成地は, 移植後, 大幅に個体数が増加し, 生育している面積も拡大傾向であった. 残り 3 地点のうち自生地と同様の落葉樹林下の 2 地点は, 移植後 14 年を経た 2009 年段階で, 開花個体 (F), 結実個体, 芽生え (S), 幼植物 (J1～J4) も生育していたが, 開花個体 (F) 数に着目すると減少傾向であった. 自生地とは立地環境が異なり, 生育に不適と考えられた 1 地点では, 個体数は減少し, 2006 年以降開花が見られない状態であった. 生活史ステージごとに収集したデータを元に, 50 年間のフクジュソウ個体群存続確率を予測した. その結果, 自生地および造成地は長期的に個体群が維持されると予測された. 自生地と同様の落葉樹林下の 2 地点は 15～17 年は維持され, 生育に不適な地点は約 6 年で消失すると算出された. 2009 年のフクジュソウ開花・結実個体数は, 移植時より多い個体数までに回復し, 生育している面積も湛水前の自生地より広くなっている. 今後も少なくとも 2 地点では長期にわたり存続が可能であり, 移植により個体群は維持できると考えられる.