A research project assessing the state of freshwater biodiversity in East and Southeast Asia was conducted from 2011-2015 to underpin the biodiversity conservation policy of the Convention on Biological Diversity. We constructed a database on the distribution of aquatic organisms and their environments, selected priority sites for conservation, and determined the anthropogenic drivers of biodiversity loss in the freshwaters of Japan. This special issue shows a portion of our findings. For lakes, more than two-thirds of selected priority sites were located in areas that were already protected; however, our assessment revealed that the species richness of both freshwater fishes and aquatic plants decreased markedly after 2001 compared with previous years. The total area of protected rivers and ponds was far beyond that proposed by the Aichi target. There were large gaps between selected sites and protected areas with rivers and wetlands. The major drivers of biodiversity loss were exotic piscivorous fishes and eutrophication in lakes and ponds, and habitat fragmentation in rivers. We found that the distribution data of indicator species were insufficient for proper assessment, and were particularly lacking in static waters (lakes, ponds, and wetlands) for the past 10-20 years.

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Approximately 86% of the wetlands in Japan are in Hokkaido. To conserve wetland ecosystems in Japan, it is important to understand the conditions and degradation of wetland ecosystems in Hokkaido. However, the information on the plant distribution in wetland ecosystems in Hokkaido is limited to studies of individual wetlands. This study created a comprehensive plant database for the wetlands in Hokkaido and evaluated the conservation priorities of wetlands, and gaps in current conservation areas. Information on plant distributions obtained after 1990 and for more than two sampling times was available for only 55 and 32 of the 155 wetlands in Hokkaido, respectively. The results indicated that few studies have evaluated the condition of wetland ecosystems in Hokkaido and more information must be compiled. Furthermore, we evaluated conservation prioritized wetlands (CPWs) using hotspot (richness and Red List species) analysis and complementarity analysis, and gaps in current conservation areas (Ramsar Convention and natural parks) using gap analysis. From the 55 wetlands, 28 CPWs were selected and only 4 of the 28 CPWs were designated as special protection zones. These findings show that more CPWs and more diverse CPWs should be selected to conserve the plant diversity of wetland ecosystems in Hokkaido.

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We prioritized Japanese lakes for aquatic macrophyte conservation using both scoring- and complementarity-based approaches employing recent (2001 and onwards) flora data. Focal lakes were scored in terms of species richness, the number of red-list species, and the extent of species persistence in and after 2001. In all, 14 lakes ranked in the top 20 on all indices, while 26 ranked in the top 20 on at least one index, suggesting that species-rich lakes tended both to host many endangered species and sustain numerous other species. Complementarity-based prioritization required 20 lakes to represent 85 species. These included both species-rich and species-poor lakes with unique species. We further prioritized lakes that had not been surveyed since 2001; future re-surveillance was planned. We identified 31 lakes that ranked in the top 20 in terms of either or both species richness and the number of red-list species. In addition, we identified another 30 lakes containing species that have not been found in other Japanese lakes since 2001. The lakes prioritized for conservation are widely distributed in Japan and are diverse in size. Attention must be paid to lakes with diverse characteristics throughout the country to conserve macrophytes.

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Lake sediments containing propagule banks are recognised as key materials to regenerate aquatic plants that have disappeared from above-ground vegetation. However, the propagules in sediments are lost over time, likely reducing the potential of plant recovery from propagule banks. This study explored the relationship between the recovery of vegetation from lake sediments and the time after disappearance from above-ground vegetation at Lake Kasumigaura (Nishiura) and Lake Inbanuma, Japan. The possibility of restoration from sediments decreases exponentially over time, and restoration becomes particularly difficult 40-50 years after disappearance from above-ground vegetation. Therefore, conservation of propagule banks should be a priority when restoring lake ecosystems.

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There is an urgent need to measure trends in biodiversity. This has not been quantified in Japanese lakes because the distribution data for freshwater species is sporadic and has not been digitized. No nationwide monitoring has been conducted since the mid-1990s. In this study, we developed a research network with regional environmental research organizations, including prefectural research institutes and museums, and assessed the biodiversity in lakes. We reviewed the literature on the distributions of strictly freshwater fish and aquatic macrophytes in 19 lakes. We also newly surveyed the presence/absence of fish in seven lakes and macrophytes in 12 lakes. Overall, the richness of native species of fish and macrophytes had declined from pre-1999 to post-2000. On average, 25% of the fish and 48% of the macrophytes species had disappeared. Many exotic fish and macrophyte species were found to have invaded these lakes, even those with high native species richness. Furthermore, the introduction of fish species native to Japan into drainages where they did not occur historically was observed in many lakes, and the numbers of translocated and exotic fish species were similar. The status of biodiversity varied greatly among the five indices we used, highlighting the need to incorporate multiple indices in biodiversity assessments. Finally, we discuss the potential and constraints of our assessment for broad-scale freshwater biodiversity monitoring.

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With rapid declines in global riverine biodiversity, conservation is needed on a nationwide scale. Since 1990, the National Census on River Environments (NCRE) has collected meaningful data on riverine organisms and environments in Japan. However, there are several issues with using the NCRE database for scientific studies. In this study, we summarised issues related to the NCRE database, and used the 3^rd NCRE dataset (2001-2005) to evaluate nationwide trends in species richness and the rarity of fishes (primarily freshwater and diadromous fishes) and taxon richness and the rarity of benthic animals (aquatic insects and shellfishes). First, we summarised data quality (e.g. monitoring sites and season) and data formatting issues (e.g. site name and species name). Second, we mitigated these potential issues as thoroughly as possible and tested the relationships of species (or taxon) richness and rarity with latitude using generalised linear models. We found that species and taxon richness showed different latitudinal distributions between primarily freshwater and diadromous fishes and between aquatic insects and shellfishes. In contrast, rarities showed spatial congruence with species diversity, suggesting that more species and rare species could be conserved in the same regions.

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Small lentic water bodies such as agricultural ponds, mire pools, floodplain pools, oxbow lakes, and lagoons around lakes play important roles in the conservation of biodiversity in terms of providing important habitats to wildlife. A geographical information system (GIS) was applied to infer the spatial distribution and relative abundance of small lentic water bodies throughout Japan using the latest geospatial data sets. We selectively sampled every polygon data for small lentic water bodies by excluding those for natural lakes, dammed lakes, rivers and small bay and those for water bodies defined not preferable to wildlife habitats such as wastewater treatment plants, industrial sites and golf yards from all open water bodies depicted in the topographical maps with the scale size of 1/25,000. These procedures revealed that inferred small lentic water bodies compiled for a unit grid with ca. 10 by 10 km distributed widely throughout Japanese terrestrial areas, and that the greater densities (442-903 polygons per an unit grid) of small lentic water bodies were detected in the coastal region of the Seto Inland Sea, where numerous agricultural ponds exist. Our GIS processed database of small lentic water bodies can provide fundamental and potential resources for assessing regional biodiversity.

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The seasonal and daily occurrence patterns of two adult fireflies, Luciola kuroiwae and Curtos okinawanus, were studied on the main island of Okinawa in 2013 and 2014. L. kuroiwae showed a single peak of seasonal adult occurrence from late April to mid May. Two peaks of adult occurrence were recognized in C. okinawanus, in May-June and September-October. Adults of L. kuroiwae and C. okinawanus were active (i.e., flashing) only immediately after sunset at most study sites. However, L. kuroiwae was observed to be active at midnight at one study site, only in 2013. This site was artificially lit until midnight, and the fireflies started to flash soon after the light was turned off. In 2014, when the light was always off, L. kuroiwae at the same site was active soon after sunset, similar to other sites. These results suggest that midnight flashing of L. kuroiwae in 2013 might have been caused by artificial lighting lasting until midnight.

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We analysed 7,091 Japanese marten (Martes melampus) faecal samples collected at Mt. Momi, Fukuoka, from 2004 to 2014 to show the effects of sika deer on the food habits of the marten. Over the last 11 years, hair of sika deer increased, while brambles (Rubus spp.) and some groups of insects decreased, in the marten droppings. These changes in the droppings seem to reflect the deer population increase. In terms of general food habits, the frequency occurrence (FO) was highest for fruits (75.6%), followed by insects (27.5%) and mammals (12.4%), and FOs of other foods were low. The FO of mammals was ca. 40% in spring and then decreased. The FO of insects was 90% from July to September and ca. 20% in other months, with high values for beetles and cicadas in July, camel crickets in August, and grasshoppers in September. The FO of centipedes increased in May. The FO of fruits (Rubus spp. and Cerasus spp.) peaked (ca. 60%) in May-June. From September on, fruits, including Actinidia arguta, Ficus erecta, and Akebia quinata, accounted for <90% of the diet. Many seeds of fleshy fruits were recovered. The FOs of Actinidia arguta, Stauntonia hexaphylla, Cinnamomum camphora, Rubus spp., Cerasus spp., Aphananthe aspera, and Eurya japonica were high (<5%). Fruits consumed by martens included large, dull-coloured, sweet-smelling species typically eaten by mammals (e.g. Actinidia arguta and Stauntonia hexaphylla), and small, colourful fruits typically eaten by birds (e.g. Rubus spp. and Eurya japonica). Many of these species are forest-edge plants.

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An alien butterfly subspecies, Hestina assimilis assimilis, has been introduced to Kanagawa Prefecture and has been established there since 1998. This species is a potential competitor for two native butterflies, H. persimilis and Sasakia charonda. In the present study, we investigated the distribution and population density of H. a. assimilis larvae from Kanagawa Prefecture to the middle of Yamanashi Prefecture during the years 2012-2014, and examined the possibility that this species might overwinter in Yamanashi Prefecture. We found that the distribution of H. a. assimilis has extended to the middle of Yamanashi Prefecture. We also found that H. a. assimilis is physiologically able to overwinter in this area, but only with difficulty due to non-physiological factors. These results suggest that the alien butterfly H. a. assimilis is invasive in Yamanashi Prefecture and will compete with native butterflies if its population density increases in the near future.

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The relationship between structural differences in irrigated rice fields (with or without open channels) and the aquatic insect fauna (Coleoptera and Hemiptera) was examined in southwestern Ehime Prefecture during the cultivation period to accumulate basic knowledge for conserving aquatic insects. Comparison of the average number of aquatic insects collected from rice fields and from open channels showed that there were more individuals in open channels than in rice fields without open channels. Rhantus suturalis, Hydaticus grammicus, Enochrus simulans, Sternolophus rufipes, and Berosus punctipennis were abundant in paddies, where these five species usually breed. Peltodytes intermedius, Haliplus sharpi, and Noterus japonicus were abundant in open channels. It is thought that P. intermedius and H. sharpi gather in open channels, which are rich in the algae they feed on. N. japonicus breeds in water and is thought to select open channels instead of ponds or marshes in areas where the dry period is short.

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[in Japanese]

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Citizen science is a recent major research approach in conservation ecology. However, citizen science focused on the publication of papers is just one part of this concept. Citizen science has broader significance that includes education, nature experience, and public awareness. To popularize citizen science and make it sustainable, it is important to redefine the concept of citizen science. In this opinion paper, we discuss the essential question “What is citizen science?” from the viewpoints of a curator in a prefectural museum, a junior high school teacher, and a researcher at a national institute. We conclude that as a whole, citizen science is not only a research approach but also serves many other functions, all of which have significance for the citizen scientist who is actively engaged in this endeavor.

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