Mitigation project of the endangered brackish water , hirosei

Mamoru Watanabe Graduate School of Life and Environmental Sciences, University of Tsukuba, Japan

Abstract

In 1998, a tiny habitat of the brackish water damselfly, , which is an endan- gered species in Japan was discovered in Ise, Mie Pref. It was a dense reed community on the brack- ish water, from which had be reclaimed under the construction of sewage plant. The local govern- ment of Mie Prefecture decided to preserve the local population of the damselfly. Then the mitiga- tion project was started, because the habitat seemed to be too small to maintain the local population, and because surroundings of the habitat would become unavailable vegetation for the damselfly due to the sewage plant development. In those days, however, there were few reports on the biology and ecology of the species. Therefore, we had to begin to clarify quantitatively the population parameters of larvae and adults, life history, behaviour, flight characteristics, body colour change for adults with age after emergence, saline tolerance of larvae as well as to measure abiotic environment, such as saline concentration, water depth, water temperature and relative light intensity in the original habi- tat, a reed community. According to the accumulation of information on the quantitative environ- mental factors, the design for a newly established habitat next to the original habitat was proposed. Then, in early spring of 2003, huge number of reed rhizomes were collected from the abandoned rice paddy fields near the original habitat, and transplanted for establishing the new habitat. Artificial brackish water was continuously supplied throughout the year. The reed community has developed year after year and nearly completed to the dense community, overcoming a lot of problems ap- peared. Techniques for estimating the number of adults and larvae in the dense reed community, and for evaluating the habitat availability, were developed. Mark-and-recapture method and line census method were adopted. Saline concentration and water supply in the artificially established habitat were monitored every week. Consequently, the adult population has increased in both the original and the established habitat. The mitigation project has now proved successful. Introduction

Loss and degradation of wetlands, particularly in estuarine areas, has been a serious issue in biodiversity conservation. In estuarine landscapes, the brackish water habitat is characterized by a subtle changing mixture of fresh water and sea tides and by mud flats of fine sedimentary material carried into the habitat from rivers and sea tides (McLusky & Elliott, 2004), and the estuarine land- scapes provide a unique habitat for species in Japan. Ponds, rice paddy fields, channels and sewage drains are the major components of these landscapes and contain varying degrees of saline water, though such water environment seems to be disadvantageous for the survival of odonate lar- vae (Corbet, 1999). Mortonagrion hirosei (Zygoptera: ) inhabits the understory of dense reed communities. It is a solitary endemic species of Japan as a brackish water damselfly, which was just discovered at Hinuma, Ibaraki, Japan in 1971, and now it is classified as an endangered species by the IUCN, principally due to habitat loss caused by practices such as river improvement and the fill- ing of wetlands (Watanabe & Mimura, 2003). Larvae of M. hirosei have a relatively high survival rate in brackish water with saline concentration of 15‰ (Iwata & Watanabe, 2004). Corbet (1999) reviewed the dragonfly's tolerance of high conductivity environments, and a few species have been found in brackish water habitats, probably because of their high saline tolerance during larval stages. Around 30 local populations of M. hirosei have been discovered, mainly on Honshu Island, Japan, and all of them are located in estuaries (Matsuda et al. 2002), and now the habitats of M. hiro- sei are declining (Hirose, 1985; Hara, 2000). Intensive conservation projects are thus essential for preventing the local extinction of the species. In Mie Prefecture, Japan, M. hirosei populations are found in a few reed communities lo- cated far apart from each other, where they form closed local populations within the habitat (Watan- abe & Iwata, 2007). Most habitats are pure dense communities of the reed, Phragmites communis, which produces a shady understory that results in low adult flight activities and subsequently a local discrete population (Watanabe & Mimura, 2004). At initial phases of the conservation planning, de- tailed information on species abundance and the habitats is lacking. Therefore, the quantitative data that can predict and evaluate the population parameters of the species are important in impact as- sessments on the artificially established habitat. In 1998, an isolated small habitat of M. hirosei was discovered in the estuarine near Miya- gawa River, Mie Prefecture, Japan, in an area where a construction project for a sewage plant was going to be undertaken (Watanabe & Mimura, 2004). Brackish water conditions in the community had been maintained by the supply of freshwater from upstream and seawater from downstream. When the sewage plant is functional, it will interfere with the supply of fresh water, resulting in the extinction of this damselfly population due to increased salinity and/or increased sediment and litter deposition in the community. Therefore, the local government of Mie Prefecture decided not only to preserve the original habitat of M. hirosei, but also to establish a new habitat to aid in the conserva- tion of this population. In order to preserve the local population of M. hirosei, a reed community was artificially established on the abandoned rice paddy fields adjacent to the original habitat by trans- planting reed rhizomes in January 2003 (Watanabe & Matsu'ura, 2006). Mitigation plans have recently become more common for conserving species in developed areas. However, an analysis of 43 habitat conservation plans in the United States found that most included little information about habitat quantity and quality (Harding et al., 2001). In the present project, we investigated the growth and microenvironment of the newly established community to evaluate its development relative to the original community, as well as the population parameter of M. hirosei. This allowed us to evaluate the mitigation project for the newly established community as M. hirosei habitat.

Species and Habitat

The endangered damselfly, M. hirosei does not perform a maiden flight (Watanabe & Mimura, 2003). Throughout their life span, adults stay among the reeds, where they show reproduc- tive behavior when sexually mature (Hirose & Kosuge, 1973; Someya, 1998; Fukui & Kato, 1999). A number of odonate studies have revealed that the sexually immature period of adults is normally the principal period of odonate dispersal (e.g. Michiels & Dhondt, 1991), and many odonate species fly a considerable distance away from water (Corbet, 1999). The immature adults of M. hirosei, however, do not leave their emergence sites. Each M. hirosei local population seems to be a relatively closed population, since its suit- able habitats are isolated from each other (Someya, 1998). The absence of detectable dispersal in immature M. hirosei makes the population structure of this species ideal for intensive study. How- ever, little attention has been paid to the population ecology of M. hirosei in Japan, probably in part due to their cryptic habits. In 1998, the discovered tiny habitat (50 m long, 10 m wide) in the city of Ise, Mie Prefec- ture, Japan, consists mainly of very slow-flowing streams with muddy bottoms flowing into fresh water from sewage and saline water from the sea, as shown in Fig. 1. The water depth was less than 10 cm in pure dense communities of the reed which produces a shady understory for the community, a relative light intensity of about 10% (Watanabe et al., 2002). The mean density of 440 live and withered reed stems per square metre corresponds to a mean distance of approximately 5 cm be- tween reed stems. No reeds were trimmed until 2001, and the community was about 2-2.5 m tall. No pesticide was used on the paddy fields during the flight season. To the east, the stream continues to Ise-Bay and the sea. Adults of M. hirosei perch mainly on live and dead shoots of reeds, preferring the tips of broken stems or the dead blades of reeds 20 cm above the water surface. Further, they show little flight activity (Watanabe & Mimura, 2004). In the area for mitigation project, four damselfly species, M. hirosei, M. selenion, Ischmura senegalensis and I. asiatica, are common in estuaries in which reed communities are dominant (Mat- su'ura & Watanabe, 2004). Iwata & Watanabe (2004) showed that young larvae of I. senegalensis have saline tolerance similar to that of M. hirosei. The two Ischnura species are regarded as being predators of M. hirosei (Hirose & Kosuge, 1973), though the two Ischnura species and M. selenion prefer open habitats, that is, along the margins of the dense reed community inhabited by M. hirosei. Therefore, as a strategy for conserving M. hirosei, these three coexisting species should be excluded.

Population Parameters in the Original Habitat

The mark-and-recapture method was used to study the population dynamics of M. hirosei adults in the original habitat from late May to early August. Adults were captured with a net and were anaesthetised by CO2. Then, each adult was marked with its own number on the undersurface of the left hind wing using a black felt-tip pen. They were released at the same site immediately after recording the date, sex and age. The marking was considered to have only minor effects on flight activities (and the probability of mating), since most of them began to fly normally and then to perch soon after recovering from the anaesthetic. Individuals injured during marking were treated as dead in the calculations. On the basis of the recapture data, seven classes were identified, mainly by wing condition and body colours, as in the case of other zygopteran species (e.g. Robertson, 1985; Watanabe & Ad- achi, 1987). As shown in Fig. 2 (Watanabe & Mimura, 2003), the categories for males were as fol- lows - T: newly emerged with soft gray bodies and soft wings; I: sexually immature with pale green thorax and gray eyes; II: older immature with green eyes; P: premature with light green thorax; M: mature with four bright green spots on the pronotum and a bright green ring on the eighth segment of the abdomen and wings with no visible damage; MM: older adult with yellow-green thorax and tat- tered wings; MMM: the oldest adults with discolored abdomen and very tattered brownish wings. For females, the same seven categories could be identified as follows. The body color and the wing condition of newly emerged females (T) were similar to those of males of the age T. Thereafter, the female body color became yellowish (I and II), but reddish-brown on the thorax (II). In addition, we identified females of age II, in which the first segment of the abdomen is red. The color of the female thorax then gradually turned to moss-green after the female matured. Females of age MMM could also be identified by a soiled abdominal tip due to oviposition. For estimating the duration of each age class, only individuals appearing in the respective age class between the first and last captures were counted. The sexually immature stage could last about 5 d. The duration of the stage MMM was not calculated according to the above definition, but we assumed that the duration was roughly equal to that of the other mature stages, M and MM, giv- ing a total mature stage duration of about 30 d. Therefore, the maximum longevity was considered to be about 35 d, assuming none was captured by a predator. Weather conditions at the study site changed dramatically during the flying season of M. hirosei. The weather was fine for both the onset of emergence and the late flying season, while the middle of the flying season coincided with the monsoon rainy season of Mie Prefecture. Anholt et al. (2001) pointed out that zygopteran species seem to survive very well in protected places on rainy days. In the microhabitat of M. hirosei, strong winds and heavy rain do not inhibit their normal be- havior, such as perching postures, cruising flight or reproductive behavior. The available space for M. hirosei activity in the reed habitat must be comparable to that of the dense forest floor. Conse- quently, the inclement weather might not have affected the population, but simply decreased the number of favorable sampling times. A single peak can be detected for each sex in late June to early July (Fig. 3). Around 150 ovarioles were found in a M. hirosei female, and the number of immature eggs per ovariole was relatively stable, being approximately 15 (Watanabe & Matsu'ura, 2006). Then, approximately 2,000 immature eggs were contained in a female. During the 3 days spent in the petri dishes for the artificial oviposition experiment, there were few submature eggs in any females. Most of the mature egg masses were laid, and others remained in the ovaries. Each female of M. hirosei had contained a total of 200 mature eggs. Assuming that there was no peculiar egg-laying pattern during 3 days, 40 eggs were laid daily.

Diurnal Behaviour of Adults Perching behaviour in relation to the sit-and-wait tactic for feeding, mating, and so on has been documented for many odonate species termed "perchers" by Corbet (1999). Shifts between perching sites, the flying behaviour as well as reproductive behaviour of M. hirosei adults were ob- served (Watanabe & Mimura, 2004). All marked individuals inhabiting the dense reed community floor were followed from sunrise to sunset. Simultaneous observation was carried out by approxi- mately 20 researchers. Every adult, sexually immature and mature, perched at 20 cm above the water surface within the reed community. For immature adults, about 120 flight activities were performed per day. When 15 feeding flights in a day were added, total flight duration must be less than 3 min per day, since each flight lasted less than 1 sec, strongly indicating that M. hirosei is a true percher. The accumulated length of the movement was 9 m per day. The low height of the perching site of M. hirosei must increase predation risk, because of the presence of frogs and spiders inside the reed community. We observed that M. hirosei adults were killed by frogs and I. senegalensis along the margins of the reed community, which is open. However, little increase in predation risk may be caused by exposure to more predators at the perch- ing sites of M. hirosei, under low light intensity among dense reed stems. Birds are not able to enter the dense reed community floor. The discovery and capture of cryptically coloured adults by poten- tial predators also seems less likely. Oviposition alone and no tandem flight might also decrease the adult mortality, because tandem pairs generally present a bigger target of predators than single indi- viduals. For sexually mature adults of M. hirosei, the number of shift flights in a day was about 90, and the number of interrupted flights and encounters were 40 and 40, respectively. Then, mature adults showed about 170 flight activities with 6 min of total flight duration per day. About 30 cm of each shift flight distance showed that their accumulated length was 27 m per day, for a total of 810 m during the mature stages. Therefore, the accumulated length of shift flights was 855 m during a maximum life span within the reed community. Because this habitat is isolated and 50 m in length and 10 m in width, however, each adult must show about 9 round trips in the reed community, sug- gesting that many encounters must take place when the population density reaches its peak. Many encounters between and/or among adults occurred resulting in fighting behaviours, such as face-to- face hovering, and no male territorial behaviour was seen in the understory of the reed community.

Mitigation Project

Because of the world wide decline of wetland areas, the construction of artificial aquatic habitats have been conducted as compensation for ecologically degraded regions (Moore, 1991; Chovanec & Raab, 1997). Bang (2001) reported the odonate species composition in a constructed wetland and the relationship between odonate communities and environmental factors which deter- mine their species richness. However, there have been few studies focusing on the conservation of a single odonate species. Although there are several projects for the habitat conservation of M. hirosei in Japan (Yamane et al., 2004), planning and monitoring based on quantitative data has not yet been reported. The artificial reed community was established on the brackish water supplied from the three outfalls as shown in Fig. 1 (ca. 10‰ salinity) with a 5-10 cm water depth. The reed rhizomes were densely transplanted in January 2003. Low depth of the brackish water with several patchy areas dried up seemed unsuitable for fishes that affect larval mortality. Before the transplantation, the abandoned rice paddy fields had been kept as a shallow open water environment, with I. senegalensis, I. asiatica, M. selenion and several anisopteran species in- habiting them (Watanabe & Matsu'ura, 2006). Because these odonate species are predators or com- petitors for M. hirosei both in the larval and adult stages (Hirose & Kosuge, 1973; Nishu, 1997; Inoue & Tani, 1999), allowing their invasion to the established habitat might affect the local popula- tion dynamics of M. hirosei. Pollard & Berrill (1992) stated that species-specific odonate larval dis- tributions are correlated with water quality. In order to prevent odonate species except for M. hirosei from immigrating to the established habitat, the water environment had to be managed and the saline water supplied at a concentration about the same as that of the brackish water in the original habitat (Matsu'ura & Watanabe, 2004). The saline concentration of brackish water has been kept at 5 to 15‰ in order to exclude I. asiatica and M. selenion from the established habitat because they had little tolerance against 15‰ salinity (Iwata & Watanabe, 2004). However, I. senegalensis seemed to have a certain saline toler- ance and to be able to inhabit a brackish water environment. There have been many reports showing that Ischnura species have as high a saline tolerance for brackish water as M. hirosei (Fox & Cham, 1994). Kefford et al. (2006) reported that I. heterosticta accelerates their larval development more under a certain concentration of saline water than in fresh water. Iwata & Watanabe (2004) also showed that both M. hirosei and I. senegalensis have almost the same saline tolerance of up to 15‰. Therefore, excluding I. senegalensis from the established reed community is critical for maintaining the local population of M. hirosei.

Reed Community as a Habitat

Shoot growth of reed began in March in the original community. The reed height was ca. 73 cm in late April, 2003, increased gradually to ca. 100 cm by mid-July, and then decreased in Sep- tember because of shoot tip breakage, as reported by Morimoto et al. (2010). Most of the reed shoots were standing dead in October. In the established community, on the other hand, shoot growth was delayed and reed height was only ca. 18 cm in late April, 2003. In late May, when adult M. hirosei emerge, reed height was 40 cm, and then increased gradually to 60 cm by mid-September. Reed height in the established community was significantly lower than in the original community throughout the 2003 growing season. Shoot density in the original community in 2003 was ca. 176 m2 in late April, and averaged 244 m2 during the flight season of M. hirosei. Shoot density in the established community in late April was 126 m2 in late April. Then, the shoot density averaged 284 m2 during the flight season of M. hirosei and increased until mid September. Therefore, shoot density did not differ between the two communities during the growing season. This growth pattern is thought to be a response to stress that occurs when reeds are damaged (Clevering, 1999; Armstrong et al., 1996a, b), suggesting that the transplantation process damaged the reed growth. The canopy of the reed communities created shade in the understory. In 2003, relative light intensity 20 cm above the water level in the original community was about 40% in late April and decreased to 10% by late June. On the other hand, relative light intensity in the established commu- nity was about 90% in late April and gradually decreased until the end of growing season. Matsu'ura & Watanabe (2004) found that adults of Orthetrum albistylum speciosum, Anax parthenope julius and Sympetrum spp. oviposited in such an open established community. Many adults of I. senegalen- sis, I. asiatica, and M. selenion were also observed in the community during the first year. Conse- quently, the established community seemed to be an unsuitable habitat for adult M. hirosei during the first year because it provided other odonate species with the open space they need for flight. In the third year after transplantation (2005), the reeds in the established community were still shorter than those in the original community during the flight season of M. hirosei. However, low relative light intensidy in the understory (less than 10%) was maintained during the flight season of M. hirosei, as was a high shoot density. Consequently, the established community was a more suitable habitat for adult M. hirosei in 2005 than in 2003. After 2006, reeds had been getting higher and crowded. The reed height increased more than 1 m and the density also increased, thus supply- ing a sufficient number of perching sites and an available light environment and becoming a suitable habitat for M. hirosei adults.

Larval Population in the Artificially Established Habitat

In the original habitat, M. hirosei larvae were only found in the spring sampling from 2004 to 2011, indicating that no other species entered the original habitat because of their low saline toler- ance and because dense reed shoots (Matsu'ura & Watanabe, 2004). Consequently, the odonate larval community was simple, as it was dominated by M. hirosei. In the established habitat, in contrast, I. senegalensis was the dominant species in the spring larval community of 2004, while a few M. hirosei larvae found suggested that a few adults immi- grated from the original habitat in 2003. In the spring sample of 2005, the number of M. hirosei lar- vae increased and then M. hirosei represented a dominant species in the larval community. M. hirosei larvae had expanded their distribution to the entire area, while the distribution of I. senegalensis had been restricted to several patchy areas with a decrease in their population. After 2006, however, small I. senegalensis populations remained with the coexistence of Sympetrum spp., in each year (Iwata & Watanabe, 2009). This result was consistent with other reports pertaining to the habitats of M. hirosei which showed that only M. hirosei larvae are collected from the reed community bed (Nishu, 1997). Therefore, from the viewpoint of the long-term population maintenance of M. hirosei, the absolute exclusion of other species, as in the original habitat, from the established habitat might be necessary as in the original habitat.

Adult Population Growth in the Artificially Established Habitat

Although using the mark-and-recapture method involves many assumptions, there was a tremendous amount of effort and skill of researchers who must place individual numbers on this or- ganism's vulnerable thin wings, as well as handle their small body when captured. Anaesthetizing such a small immediately after capturing is needed to stay still for a few minutes to write numbers, to measure the body size, and to identify the age, and also for the insects to show their normal behaviour after release. In addition, several days of good weather during the flying season are required; unfortunately, this is the rainy season in Japan. The high density of tough reed stems also inhibits sweeping a particular area with a net in order to capture successfully adults perching in the understory of the community without disturbance of other perching individuals. Furthermore, the impact of repeated recapturing might present an increased risk of injury to the adult . There- fore, census counts using the line transect method might provide a good alternative method of ob- taining a population estimate, due to the lack of direct physical contact with the organism. The line transect method also requires fewer person-days of effort than does the mark-and-recapture method, and is appreciably more cost effective in terms of assessing damselfly numbers. However, it is not so easy to determine the relationship between the line transect method and the mark-and-recapture methods in terms of the estimated numbers of odonate species. Various line transect methods are widely used for estimating abundance (Southwood & Henderson, 2000). Generally, an observer travels along a line, recording any detected. However, there have been no reports that examine any relationships between resules from the mark- and-recapture method and the line transect method to population estimations. We compared the estimate of M. hirosei abundance obtained by the line transect method and by the mark-and-recapture method. Since M hirosei adults are perchers, and are distributed across the floor of reed communities (Watanabe et al., 2002), the census count was deemed effective for assessing the abundance of this species. The results presented here pave the way for a discussion of approaches to monitoring population for conservation of this species (Watanabe & Iwata, 2007). Census counts of M. hirosei using the line transect method were carried out weekly in the original reed community from July to August of 2003 (total: 4 counts), and from May to July of 2004 (total: 12 counts). In order to exclude the effect of adult distribution in the community due to disturbance caused by the mark-and-recapture sampling, each census count in the line transect method was conducted at least three days after the mark-and-recapture sampling. We counted all perching adults of both sexes (lone individuals and tandem pairs) detected by walking a 89 m line, with 0.5 m on both sides of the line (Watanabe & Iwata, 2007). This line winded large its way across the reed community. Because the walking itself might disturb the perching behaviour of adults re- sulting in the decline in the numbers of adults along the line, the census count was once for about 1 hour in the reed community around noon. We marked 2,961 males (740 recaptured at least once) and 2,212 females (465 recaptured) throughout the flying season of 2003. Using both Jolly's model and the Manly and Parr model (as described in Southwood & Henderson, 2000), the daily change in the estimated number was similar between the models. On the other hand, 1,560 males and 1,845 females were marked from late June to mid July of 2004. In accordance with Watanabe & Iwata (2007), the estimated daily number of adults per m2 (N) could be calculated from the following relations: for males, log N = -0.29+0.64 log D for females log N = -0.28+0.71 log D, where D signifies the number of males or females along a 10 m line. In 2003, the first year of the artificially established reed community, a few adults were de- tected in early June the nearest to the original habitat, and the number of adults counted increased slightly in July. Only one female was found in July, and no tenerals (one day old adults just after emergence) were observed throughout the flying season. Therefore, about 1,000 adults were esti- mated in the established reed community, and all the adults were immigrants from the original habi- tat. In 2004, about 800 males and 800 females were estimated as the daily density in late June, indicating the presence of more than 1600 adults daily, which is about 0.8 individuals per m2. In late June in 2005 and 2006, therefore, the estimated daily numbers of each sex were around 2,000 and 5,000. Each change in the daily estimated number of adults in the census line for four years fit an approximate quadratic regression curve with a single peak, i.e., a parabola. In order to estimate the total number of males in the population, each positive area of the parabola was calculated, and the sum of the daily numbers were divided by the mean longevity of males, 7.5 days, a value that was based on either the daily estimated survival rate or the daily estimated number of emergences calcu- lated by mark-and-recapture survey in 2003 (Watanabe and Iwata, 2007). The total number of males was obtained by doubling the number of males. The total number of adults in the population in the established habitat was about 10,000 in 2004 and 23,000 in 2005. In 2006, the number of adults grew to 45,000. The estimated density in the established habitat was increased year by year, and in 2006, it was almost equivalent to that in the original habitat (Fig. 4).

Discussion

Since the 1971 discovery of M. hirosei in Japan, the species had undergone an alarming de- cline, and 9 out of the 26 populations originally found were thought to be at risk of extinction (Som- eya 1998). Later, more than 6 new habitats were discovered. The decline recorded in most of the local populations could have been caused by habitat degradation (Nishu 1997), though little informa- tion on the ecology of the species was available. M. hirosei adults have low dispersion ability, and no emigrants have been observed in the reed community, suggesting that such high site fidelity has serious implications for conservation (Watanabe & Mimura, 2004). Intensive management on the artificially established reed community has played a substantial role in the expansion of this damselfly species. The dense reed community has continued to develop 3 years after the reed rhizomes transplanted (Matsu'ura & Watanabe, 2006), thus counteracting the loss of the rice paddy fields. Yamane et al. (2004) tried to establish a reed community as a M. hirosei habitat and has succeeded in developing the reed community through careful management, though the insect population has unfortunately declined. Over nine years (2003 - 2011), the total population in the original habitat was stable at 15,000 to 20,000 individuals, and the estimated daily number in the peak flying season was more than 3,000, or about more than 3.5 individuals per m2. In the established habitat, on the other hand, the estimated number of total adults throughout the flying season of 2003 was 1000, indicating that 6.7% of the original population immigrated. In 2004, the adult population included both the immi- grants and the insects that emerged from the established habitat, and the estimated total population increased to 10,000. In 2005, an estimated 23,000 individuals were found all over the established habitat. In 2006, the number of adults was estimated to be more than 45,000 and reached 20 per m2 (Fig. 4), which was equal to that of the original habitat. Therefore, we can conclude that the damsel- fly has successfully settled in the established habitat (Watanabe et al., 2008). Habitat loss and fragmentation were the major contributing factors in the decline of M. hiro- sei (Someya, 1998). Plant succession of the reed community eventually becomes an unsuitable habi- tat due to the drying up of the reed bed. Factors in the biotic environment such as predation pressure also contribute to the population decline when the habitat is semi-shade. This implies that further deliberate efforts to conserve the species should concentrate on attempting to maintain the dense reed community with high saline water. Therefore, this research highlights an important approach to the protection of an endangered species. The maintenance of the M. hirosei population in the estab- lished reed community may require an actual dense reed community that supports both the larval and adult stages. In conclusion, it is clear that artificially maintaining a dense reed community and keeping a brackish water environment resulted in an increase in the M. hirosei population. This study demon- strated that low species richness at a newly constructed habitat was optimal for conservation of a particular species which can adapt to a severe abiotic environment.

Acknowledgements

I would like to thank the Ise Branch of the Mie Prefectural Government for their hospitality at the study site and for giving me research permission. Tamano Consultants Co., Ltd. also assisted me. I would also like to thank Y. Mimura, T. Higashi, R. Watanabe, S. Matsu'ura, K. Susa, Y. Tera- moto, and M. Morimoto for their assistance in the field. This study was partially supported by The Foundation for the Zoshinkai Fund for the Protection of Endangered Animals, the Foundation of River and Watershed Environment Management (FOREM), Japan, Espec Foundation For Earth En- vironmental Research and Technologies (Charitable Trust), the Pro Natura Foundation and AEON Environmental Foundation.

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Map of the study area including the original habitat and the artificial established habitat. Each dot shows a quadrate for sampling Odonata larvae. Three open squares indicate the outfalls which sup- plied brackish water to the established habitat. Striped rectangles indicate residences. Figure 2. Seven age class for both sexes, estimated by wing condition and body colours after emergence. Figure 3. Changes in the estimated daily number of adult M. hirosei in the original habitat in 2003. Figure 4. Yearly changes in the estimated size of adult population (per 100 m2) of M. hirosei in the original and established habitat.