Jpn. J. Environ. Entomol. Zool. 31（1）：1－12（2020） 環動昆 第 31 巻 第 1 号：1－12（2020） Original Article Species diversity of Odonata in Nakaikemi Marsh, Fukui Prefecture, Japan Norio Hirai＊, Takashi Morioka and Minoru Ishii Graduate School of Life and Environmental Sciences, Osaka Prefecture University, 1-1 Gakuen-cho, Nakaku, Sakai, Osaka 599-8531 Japan （Received: June 5, 2018; Accepted: February16, 2020） Abstract Nakaikemi Marsh was designated as a wetland of international importance under the Ramsar Convention on Wetlands in 2012 because of its rich species diversity and the presence of threatened and endangered animal and plant species. Although the marsh had been maintained using traditional methods for centuries as rice paddy fields, land use has changed since the abandonment of cultivation in the 1990s. In this study, species diversity of Odonata in the marsh was investigated once a month between April and November 2012 using line-transect and point-census methods for adults and a netting method for larvae. We recorded adults and larvae of 50 Odonata species; a total of 2093 adults from 47 species and 503 larvae from 27 species were observed in the eight surveys. Most of the species found in this study were those recorded in the past, but Aeschnophlebia longistigma, Aeschnophlebia anisoptera, and Nannophya pygmaea, which had been continuously observed in the early 1990s, were not recorded. In contrast, we found increased numbers of Rhyothemis fuliginosa, Ischnura senegalensis, and Sympetrum croceolum around the newly formed Sasahana Pond. A population analysis using Kimoto’s similarity index (Cπ) revealed that the odonatan assemblage around the pond differs from those in other areas in Nakaikemi Marsh. It is possible that the Sasahana Pond has become one of the most important odonatan habitats in the marsh. We found several endangered species and the second highest species richness and diversity in the Ushirodani Valley adjoining the marsh, where traditional methods are used to maintain paddy fields. Invasive alien plant and animal species such as Solidago altissima and Procambarus clarkii were widespread across the whole area and are considered to harm native vegetation and aquatic animals in the marsh. Our findings indicate that P. clarkii density has a significant negative effect on the species diversity of Odonata larvae in the marsh. Keywords: aquatic insects, community ecology, damselfly, dragonfly, Procambarus clarkii Introduction designated as a wetland of international importance under the Ramsar Convention on Wetlands in 2012 (The Ramsar Nakaikemi Marsh, located at an elevation of 47 m a.s.l. in Convention on Wetlands, 2012). Tsuruga City, Fukui Prefecture, Japan, is a 25-ha basin In 1990, a bypass highway was built, and excavated soil surrounded by hills (Saito, 2008). The central part of the site is from its construction was deposited in the marsh. As a result, composed of peat sediment that is approximately 40 m in depth several ponds formed by heavy soil were connected and and represents a record of climate and vegetation changes became a large pond (Nakamoto et al., 2003; Shimoda and during the past 100,000 years (Sakamaki, 2003; Ramsar Nakamoto, 2003), which is called Sasahana Pond. The Tsuruga Convention on Wetlands, 2012). This marsh is also considered City government invited a gas company to build liquified a biodiversity hotspot with more than 2000 species of animals natural gas tanks on the marsh in 1992, and cultivation of the and plants (Watanabe and Kawano, 2003; Ramsar Convention paddy fields was abandoned after the company took possession on Wetlands, 2012). For this reason, the Nakaikemi Marsh was of the marsh (Shimoda and Nakamoto, 2003). However, *Corresponding author: [email protected] - 1 - Hirai et al Fig. 1 Location of the study site, Nakaikemi Marsh, Tsuruga City, Fukui Prefecture, Japan, and the transect route for Odonata survey. Adult survey sections are A to J; Aeshnidae observation points are K & L; and larvae survey points are Q to Z. construction of the liquified natural gas tanks was canceled in was newly recorded in 2011 (Fujino and Wada, 2011) and 2002 (Sasaji et al., 2003), and the gas company donated the Gynacantha japonica was found in 2013 (M. Uenoyama, property to Tsuruga City in 2005 (Sasaki, 2006). Prior to the personal communication), bringing the total number of abandonment of the paddy fields in Nakaikemi, the marsh recorded species to 72. However, the populations of some consisted of various aquatic and semi-aquatic environments: Odonata species declined remarkably between 1995 and 2003 cultivated paddy fields, fallow fields, abandoned fields, ponds, due to deterioration of their habitats in the marsh (Tsubaki and and channels (Wada, 2000). Since rice farming ceased, Kawano, 2003), and a comprehensive survey of Odonata however, vegetative succession has progressed, water levels species has not been carried out since Wada (2003) and have declined due to lack of management, and stagnation and Nakamoto et al. (2003) performed them. After 2003, plant deterioration of water quality have occurred as pathways have succession advanced; a large deep pond was expanded; and been constructed in the marsh (Shimoda and Nakamoto, 2003; alien species, such as Solidago altissima and P. clarkii, invaded Hoshina et al., 2007). The population of the invasive alien red more of the marsh. Therefore, we expected to find that the swamp crayfish, Procambarus clarkii, has exploded, Odonata assemblage, which previously consisted of destroying populations of native aquatic animals and plants shallow-marsh species, had shifted to that of deep-pond species. (Wada, 2001; Shimoda, 2003; Hoshina et al., 2007). To clarify whether this habitat shift was accompanied by a shift Odonata species are an important and widespread biological in the Odonata assemblage, research on the different water indicator of the condition and biodiversity of freshwater types and effects of alien species was needed. In 2012, we ecosystems (Corbet, 1962; Steytler and Samways, 1995; Wada, measured the species diversity of Odonata in Nakaikemi Marsh 2000; Inoue, 2010a). Habitat preference also varies among and analyzed recent changes in the assemblage structure as species, with some Japanese species preferring lotic water and compared with past records. others deep lentic or shallow lentic waters (e.g., Kadoya and Washitani, 2007; Kadoya et al., 2009; Inoue, 2010b). In Materials and Methods Nakaikemi Marsh, 70 species of Odonata in 11 families were recorded prior to 2002 (Nakaikemi Wetland Trust, 2002; Study sites and methods Nakamoto et al., 2003; Wada, 2003). Sympetrum croceolum The field surveys were carried out once a month from April - 2 - Cocoon color morphs of Monema flavescens Table 1 Description of Odonata survey location sections, landscape, and vegetation components of the study area, Nakaikemi Marsh, Tsuruga City, Fukui Prefecture, Japan in 2012. Survey place Landscape component Vegetation Section AB Gravel path between Sasahana Pond and deciduous forest Tall herbaceous plants such as the common reed Phragmites [Points Q, R and S] communisand reedmace, Typha spp., were growing in the deep Transect length: 456 m ponds. Section BC Gravel path along the western edge of the marsh Tall herbaceous plants such as the common reed, Phragmites [Point T] communis, and the invasive introduced goldenrod, Solidago Transect length: 341 m canadensis, were growing in shallow mud. Section CD&EG Soil path along the northeastern edge of the marsh. Northern side Tall herbaceous plants such as the common reed, Phragmites [Points U and W] was deciduous forest and southern side was wet mud flats. communis, and the invasive goldenrod, Solidago canadensis, Transect length: 686 m were growing in the shallow mud. Section DE Soil path between a shallow small pond and the marsh. Short herbaceous plants such as cogongrass, Imperata [Point V] cylindrica, were growing along edge of the small pond. Transect length: 46 m Section EF Slope behind the small pond with water exudation from forest. Shrubs and short herbaceous grass. Transect length: 111 m Section GH Ushirodani Valley, comprising branched waterways and paddy Almost all areas were abandoned paddy fields traces covered [Points X, Y and Z] fields. with tall herbaceous plants, but the most eastern area had always Transect length: 859 m had water and tall and low herbaceous plants. Section IA&AJ One-meter wide waterways with bottoms covered with slime. Short herbaceous grass. Transect length: 299 m to November 2012 in Nakaikemi Marsh, Tsuruga City, Fukui basin. Physical details of the adult survey transect sections are Prefecture, Japan (35°39’N, 136°05’E; Fig. 1). given in Table 1. To assess the relationship between environmental factors To identify whether Odonata species are breeding in the and the Odonata assemblage, Odonata adults were recorded marsh, Odonata larvae were captured by sweeping a D-frame along seven line transects and at two point-census locations. In aquatic insect net (40 cm wide; 1-mm mesh) through the water the transect-census method, the study area was divided into at 10 locations (points Q to Z) in the study area on the same two landscapes: basin and valley. In the basin landscape, a days as the adult surveys were conducted (Fig. 1). The insect 1.8-km route that circled through major landscape components net was then moved 1 m, and this sampling was repeated 10 was fixed and divided into six sections according to times per point as a rule. When the water depth was reduced, surrounding landforms. In the narrow 0.8-km-long valley we decreased the number of sweeps. The density of larvae landscape (Ushirodani Valley), we fixed a single transect. (number / 10 netting sample) was calculated by dividing the Water flows out from the basin area into Ushirodani Valley, total number observed by the total number of sweeps at each which is separated from the rest of the marsh and contains point (for the total number of sweeps conducted in each survey, cultivated and fallow paddy fields surrounded by deciduous see Table 4).