Physical habitat characteristics of freshwater crayfish Cambaroides similis (Koelbel, 1892) (Arthropoda, Decapoda) in South Korea (original) (raw)

Jin-Young Kim1 , Yong Ju Kwon2 , Ye Ji Kim2 , Yeong-Deok Han1 , Jung Soo Han1 , Chae Hui An1 , Yong Su Park1 and Dongsoo Kong2*

1Research Center for Endangered Species, National Institute of Ecology, Yeongyang 36531, Republic of Korea
2Department of Life Science, Kyonggi University, Suwon 16227, Republic of Korea

Correspondence to: Dongsoo Kong
E-mail dskong@kyonggi.ac.kr

Received: August 7, 2023; Revised: October 13, 2023; Accepted: November 14, 2023

This article is licensed under a Creative Commons Attribution (CC BY) 4.0 International License, which permits use, sharing, adaptation, distribution and reproduction in any medium or format, as long as you give appropriate credit to the original author(s) and the source, provide a link to the Creative Commons license, and indicate if changes were made. The images or other third party material in this article are included in the article’s Creative Commons license, unless indicated otherwise in a credit line to the material. If material is not included in the article’s Creative Commons license and your intended use is not permitted by statutory regulation or exceeds the permitted use, you will need to obtain permission directly from the copyright holder. To view a copy of this license, visit http://creativecommons.org/licenses/by/4.0/ The publisher of this article is The Ecological Society of Korea in collaboration with The Korean Society of Limnology

Abstract

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• Abstract
• Introduction
• Materials and Methods
• Results
• Discussion
• Conclusions
• Acknowledgements
• Abbreviations
• Authors’ contributions
• Funding
• Availability of data|materials
• Ethics approval and consent to participate
• Consent for publication
• Competing interests
• References

Background: Cambaroides similis is an endangered candidate species living in the stream of South Korea. Freshwater crayfish is known to decline rapidly not only domestically, but also internationally. Its decline is projected to be further exacerbated due to climate change. Understanding physical characteristics of the habitat is crucial for the conservation of an organism. However, comprehensive data regarding the distribution and physical habitat characteristics of C. similis are currently unavailable in South Korea. Thus, the objective of this study was to ascertain preferred ranges for water depth, current velocity, and streambed substrate of C. similis using Weibull model.
Results: In this study, C. similis was found at 59 sites across 12 regions in South Korea. Its optimal water depth preferences ranged from 11.9 cm to 30.1 cm. Its current velocity preferences ranged from 9.8 cm s–1 to 29.1 cm s–1. Its substrate preferences ranged from –5.1 Φm to –2.5 Φm. Median values of central tendency were determined as follows: water depth of 21.4 cm, current velocity of 21.2 cm s–1, and substrate of –4.1 Φm. Mean values of central tendency were determined as follows: water depth of 21.8 cm, current velocity of 22.0 cm s–1, and substrate of –4.4 Φm. Mode values of central tendency were determined as follows: water depth of 21.7 cm, current velocity of 20.1 cm s–1, and substrate of –3.7 Φm.
Conclusions: Based on habitat suitability analysis, physical microhabitat characteristics of C. similis within a stream were identified as Run section with coarse particle substrate, low water depth, and slow current velocity. Due to high sensitivity of these habitats to environmental changes, prioritized selection and assessment of threats should be carried out as a primary step.

Keywords: Cambaroides similis, current velocity, endangered candidate species, streambed substrate, water depth, Weibull model

Introduction

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• Abstract
• Introduction
• Materials and Methods
• Results
• Discussion
• Conclusions
• Acknowledgements
• Abbreviations
• Authors’ contributions
• Funding
• Availability of data|materials
• Ethics approval and consent to participate
• Consent for publication
• Competing interests
• References

The freshwater crayfish, Cambaroides similis, is known to inhabit certain regions including the Korean Peninsula and parts of China (Lianshanguan, Qian Shan, Gai Xian, and Wanjialing) (Kawai and Min 2005). It is primarily found in slow-flowing sections of small streams or valley pools. It is often found between rocks and leaf litter. In South Korea, the population of C. similis has decreased to the point where it is designated as an endangererd candidate species. It is necessary to conduct regular monitoring to protect and manage this species due to habitat development, climate change, and competition with invasive species. While research has been conducted on the morphology (Kawai and Min 2005), life history (Jung et al. 2009; Ko and Kawai 2001), genetics (Ahn et al. 2011; Kim et al. 2012), and parasites (Song et al. 2017) associated with C. similis, comprehensive studies on its ecological characteristics related to its physical habitat have not been reported yet.

To preserve the habitat of wildlife, it is important to understand physical characteristics of target species habitats. Streams, in particular, undergo changes in physical environments such as slope, light, and flow as they progress from upstream to downstream, which can influence compositions of biological communities (Vannote et al. 1980). In the case of benthic macroinvertebrates inhabiting streams, current velocity, water depth, and substrate composition are among the most important factors (Kim 2014; Kong and Kim 2017; Orth and Maughan 1983; Pan et al. 2015). Substrates such as rocks and gravel dominate in high-velocity streams (Church 2002) while sediment particles like sand are more prevalent in low-velocity streams (Colby 1964).

We estimated habitat suitability index (HSI) for C. similis in terms of water depth, current velocity, and substrate using the Weibull model (Weibull 1951). HSI is a quantitative means of interpreting the preference of aquatic organisms for different environmental conditions (Vadas and Orth 2001; Vismara et al. 2001). Typical method for calculating HSI involves dividing the number of individuals presenced at a specific environmental factor value by the maximum number of individuals observed at any value (Ahmadi-Nedushan et al. 2006). This typical approach requires interpolation for calculating HSI values, which can be cumbersome and difficult in terms of recording. In contrast, using a continuous function allows us to directly obtain HSI values corresponding to specific environmental factor values with advantages of easy record-keeping and consistent reproducibility (Kong and Kim 2017).

Mathematical models have long been used to interpret the relationship between a survey area or population size and the number of species (Arrhenius 1921; Gleason 1922; Kylin 1926; Preston 1948, 1962; Weibull 1951). Flather (1996) has applied nine mathematical models to interpret the relationship between the number of bird species and survey area, confirming the Weibull model as the most suitable model. Kong and Kim (2015) have analyzed the relationship between the number of benthic macroinvertebrate species and survey area in riffle sections of Gapyeongcheon and Osancheon using five mathematical models and found that, the Weibull model is the most suitable one. Recently, studies have been conducted using the Weibull model to calculate physical HSI for fish and benthic macroinvertebrates (Kim and Kong 2018; Kim et al. 2022; Kong and Kim 2017; Kong et al. 2017). Based on these research studies, the adequacy of the Weibull model has been sufficiently validated.

Due to increasing occurrence of strong rainfall caused by climate change, there has been a significant fluctuation in water levels and exposure to artificial habitat disturbances such as stream channel modifications, resulting in physical habitat degradation (Kong and Kim 2016). Additionally, there is a growing concern over the expansion of the habitat range of invasive species such as the red swamp crayfish, leading to competition for habitat and the potential spread of crayfish plague (Aphanomyces astaci) among C. similis populations. For these reasons, the purpose of this study was to analyze physical habitat characteristics of C. similis to provide essential information for habitat conservation.

Collection of Cambaroides similis survey data

In this study, a total of 169 sites nationwide were directly sampled for habitat presence and C. similis density (individuals m–2) from April 2023 to June 2023. These survey sites were selected using results from “National Ecosystem Survey ('14–'19),” “Ecosystem Survey in Baekdudaegan Protected Area ('14–'17),” “Intensive Survey on Special Area ('15–'17)” conducted by the National Institute of Ecology, the “Stream/River Ecosystem Survey and Health Assessment ('16–'21)” conducted by the Ministry of Environment and the National Institute of Environmental Research, and Specimen Information of Nakdonggang National Institute of Biological Resources ('13–'22). The sampling method followed guidelines for surveying and assessing benthic macroinvertebrates as stated in the announcement No. 2016-372 by the National Institute of Environmental Research.

Measurement of environmental factors

Data measured and utilized for analyzing physical habitat characteristics of C. similis included water depth (D, cm), current velocity (U, cm s–1), and streambed substrate particle size (Φm). Water depth (D) was measured using a 100 cm steel rulrer, from the substrate surface where C. similis was found to the water surface. Current velocity (U) was calculated using the Craig method (Craig 1987), which applies the difference in water depths measured parallel and perpendicular to the streams’s current direction, following guidelines for surveying benthic macroinvertebrates (Eq. 1).

Eq. (1)U=2g(D2−D1)

D1: water depth (cm) in the direction parallel to the water flow

D2: water depth (cm) in the direction perpendicular to the water flow

g: gravitational acceleration (981 cm s–2)

Streambed substrate particle size (Φm) was classified into five categories based on the area ratio of the substrate surface following the criteria proposed by Cummins (1962) (Table 1). While the surface area ratio of substrate particle size maight have less precision than the weight composition ratio, it ensures that no organisms are lost during the measurement process (Kong and Kim 2017). Additionally, it provides an easy evaluation of the arrangement of substrate materials (Bovee 1986), making it more suitable for analyzing ecological characteristics of C. similis that inhabit underneath the substrate. Following Kong and Kim (2016), the average particle size was calculated using the area ratio of the substrate surface (Eq. 2).

Table 1 . Terminology and classifications for substrate particle size.

Revised from the article of Cummins (Am Midl Nat. 1962;67(2):477-504).

Eq. (2)Φm= ∑riΦi

Φm: the mean Φ value of grain size in streambed

ri: the areal ratio of grain size i interval

Φi: the median Φ value of grain size i interval

Analysis of physical habitat characteristics of Cambaroides similis using mathematical models

The total number of individuals within each range of physical environmental factors was divided by the number of presences to calculate individual density. Ranges were subdivided based on characteristics of each factor (D: 10 cm, U: 10 cm s–1, Φm: 1.5). The suitable habitat range for C. similis based on each environmental factor was analyzed using the HSI, applying a modified Weibull model (Eq. 3), which has been previously used in studies on fish and benthic macroinvertebrates (Kim et al. 2022; Kong and Kim 2017). The cumulative density function (CDF) (Eq. 4), probability density function (PDF) (Eq. 5), and parameters (κ, λ, c) could minimize normalized root mean squared error (NRMSE) between cumulative mass function (CMF) and CDF (Eq. 6) were extracted following Kong and Kang (2023) and utilized in the analysis of habitat suitability. κ represents the shape parameter. λ represents the scale parameter and c represents the location parameter or threshold parameter. Current velocity (x) cannot have negative values (0 ≤ x ≤ ∞), while factor values (x) of Φm (–∞ ≤ x ≤ ∞) and c value of water depth (–c ≤ x ≤ ∞) can have negative values (Kong et al. 2017). Therefore, following Kong and Kim (2017), calculations were performed for mean, median, mode, standard deviation, and values corresponding to specific probabilities using the range of factor values (x) as a reference. HSI numerically ranged from 0 to 1. Finally, following the criteria of Bovee (1986), threshold values (50%, 75%, 90%, 95%) for water depth, current velocity, and substrate particle size were derived, and the suitable habitat range was based on the 50% threshold value. Parameters κ, λ, and c were analyzed using CurveExpert professional Ver. 2.7.3 (Hyams Development) while CDF, PDF, NRMSE, and adjusted HSI were analyzed using Excel from Microsoft Office Standard 2016, including its functions and solver feature.

Eq. (3)HSI= k−1k1−kkx+cλk−1ek−1k−x+cλk

κ = shape parameter

λ = scale parameter

c = location parameter or threshold parameter

Eq. (4)fx= 1−1αe−x+cλk
α= e−cλk
Eq. (5)fx= 1αkλx+cλ k−1e−x+cλ k

α = cummulative probability except dummy range below zero value of environmental variables (1 for mean diameter of sediment grain as phi value)

Eq. (6)NRMSE %=1k∑i=1kCMFi−CDFi21k∑i=1kCMFi×100

Results

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• Abstract
• Introduction
• Materials and Methods
• Results
• Discussion
• Conclusions
• Acknowledgements
• Abbreviations
• Authors’ contributions
• Funding
• Availability of data|materials
• Ethics approval and consent to participate
• Consent for publication
• Competing interests
• References

Habitat distribution of Cambaroides similis

A total of 169 sites were surveyed and C. similis was found at 59 sites across 12 regions (Fig. 1, Table 2). Among these regions, Jeollanam-do exhibited the highest occurrence frequency with 13 sites, followed by Chungcheongbuk- do with 9 sites, Gyeonggi-do with 7 sites, Gyeongsangnam- do with 6 sites, Incheon, Busan, and Chungcheongnam-do with 5 sites each, Gangwon-do with 4 sites, Gyeongsangbuk-do with 2 sites, and Seoul, Daejeon, and Jeollabuk-do with 1 site each. The highest individual density was observed in Gyeonggi-do with 25 individuals m–2, followed by Incheon with 21 inds m–2, Gangwon-do with 16 inds m–2, Gyeongsangnam-do with 14 inds m–2, Chungcheongnam-do with 13 inds m–2, Jeollanam-do with 12 inds m–2, Chungcheongbuk-do with 11 inds m–2, Busan with 10 inds m–2, Daejeon, Gyeongsangbuk-do and Jeollabuk-do with 7 inds m–2 each, and Seoul with 4 inds m–2.

Table 2 . Number of habitat regions, survey and presence sties, individual density of Cambaroides similis.

Figure 1. Map of South Korea, the southern half of the Korean Peninsula bordering the East Sea and Yellow Sea, Northeast Asia; and habitats of Cambaroides similis (presence: 59 red circles, absence: 110 grey triangle).

Water depth

Based on characteristics of occurrence within different water depth intervals, the Weibull model was derived and parameters (κ, λ, c) along with central values (mean, median, mode), standard deviation, and NRMSE were calculated. The NRMSE between the CDF and the CMF showed a high level of accuracy at 3.09%. Parameters κ, λ, and c were determined as follows: κ = 19.4, λ = 314.6, c = 292.0. Central values were found to be as follows: mean value of 21.8 cm, median value of 21.4 cm, and mode value of 21.7 cm. The standard deviation was 12.0 cm. It was observed that mode and median values were slightly smaller than the mean value, indicating a positively skewed distribution (Table 3). Cambaroides similis showed the highest occurrence rate in shallow depths of 10–20 cm (Fig. 2A, B). Based on the analysis of habitat suitability for water depth, the adjusted HSI for C. similis was calculated using Instream Flow and Aquatic Systems Group’s (IFASG’s) criteria (Bovee 1986). Suitable depth range for species was determined to be 11.9 cm to 30.1 cm (Fig. 2C).

Table 3 . Values of Weibull distribution function, NRMSE, and HSI of water depth.

Values of Weibull distribution function parameters, central tendency, standard deviation, normalized root mean squared error (NRMSE) of water depth and critical values of water depth preference range at adjusted habitat suitability index (HSI) of Cambaroides similis, which were transformed based on the Bovee (1986) guideline.

Figure 2. Water depth (A) probability mass function (PMF) and probability density function (PDF), (B) habitat suitability index (HSI), and (C) adjusted HSI according to the guideline of Bovee (1986) for Cambaroides similis.

Current velocity

Using characteristics of occurrence within current velocity intervals, the Weibull model was formulated and parameters (κ, λ, c) were determined along with central values (mean, median, mode), standard deviation and NRMSE. The NRMSE between the CDF and the CMF showed a high level of accuracy at 3.31%. Prameters κ, λ, and c were determined as follows: κ = 15.0, λ = 275.5, and c = 254.1. Central values were found to be as follows: mean value of 22.0 cm s–1, median value of 21.2 cm s–1, and mode value of 20.1 cm s–1. The standard deviation was 12.8 cm s–1. It was evident that both mode and median values were lower than the mean value, implying a positively skewed distribution (Table 4). Cambaroides similis primarily occurred in slow current velocity intervals of 10–20 cm s–1 (Fig. 3A, B). Using the analysis of habitat suitability for current velocity, the adjusted HSI for C. similis was calculated following the criteria of the IFASG’s criteria (Bovee 1986). The suitable range of current velocity for the species was found to be between 9.8 and 29.1 cm s–1 (Fig. 3C).

Table 4 . Values of Weibull distribution function, NRMSE, and HSI of current velocity.

Values of Weibull distribution function parameters, central tendency, standard deviation, normalized root mean squared error (NRMSE) of current velocity and critical values of current velocity preference range at adjusted habitat suitability index (HSI) of Cambaroides similis, which were transformed based on the Bovee (1986) guideline.

Figure 3. Current velocity (A) probability mass function (PMF) and probability density function (PDF), (B) habitat suitability index (HSI), and (C) adjusted HSI according to the guideline of Bovee (1986) for Cambaroides similis.

Streambed substrate

The Weibull model was constructed based on characteristics of occurrence within streambed substrate intervals, resulting in the determination of parameters (κ, λ, c) along with central values (mean, median, mode), standard deviation and NRMSE. The NRMSE between the CDF and the CMF showed a high level of accuracy at 2.52%. Parameters κ, λ, and c were determined as follows: κ = 9.0, λ = 15.9, and c = 19.4. Central values were found to be as follows: mean value of –4.4, median value of –4.1, and mode value of –3.7. The standard deviation was 2.0. It was observed that mode and median values were larger than the mean value, indicating a negatively skewed distribution (Table 5). The C. similis primarily occurred in the substrate with a coarse particle diameter (–Log2Dm: –5.5 to –4.0) (Fig. 4A, B). Based on the analysis of streambed substrate habitat suitability, the adjusted HSI for C. similis was calculated using guidelines provided by the IFASG’s criteria (Bovee 1986). The species was found to have a suitable range of streambed substrate between –5.1 and –2.5 (Fig. 4C).

Table 5 . Values of Weibull distribution function, NRMSE, and HSI of streambed substrate.

Values of Weibull distribution function parameters, central tendency, standard deviation, normalized root mean squared error (NRMSE) of substrate and critical values of substrate preference range at adjusted habitat suitability index (HSI) of Cambaroides similis, which were transformed based on the Bovee (1986) guideline.

Figure 4. Substrate (A) probability mass function (PMF) and probability density function (PDF), (B) habitat suitability index (HSI), and (C) adjusted HSI according to the guideline of Bovee (1986) for Cambaroides similis.

Discussion

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• Abstract
• Introduction
• Materials and Methods
• Results
• Discussion
• Conclusions
• Acknowledgements
• Abbreviations
• Authors’ contributions
• Funding
• Availability of data|materials
• Ethics approval and consent to participate
• Consent for publication
• Competing interests
• References

C. similis was found not only in the middle and southern regions of the Korean Peninsula but also throughout islands of Yellow Sea (such as Ganghwa-do, Yeongjong-do, Deokjeok-do, Baengnyeong-do, etc.) (Kawai and Min 2005). Although the presence of C. similis was not surveyed in all inland or islands, the present study still confirmed various locations inhibited by C. similis throughout inland regions of South Korea. However, since there were no prior quantitative studies on nationwide distribution or population density of C. similis, comparative analysis of population size with results of this study could not be perforemed. Therefore, C. similis distribution and quantitative population density found in this study could be used as essential foundational data for assessing future changes in the population size of C. similis.

Kawai and Min (2005) have suggested habitat characteristics of C. similis as follows: (1) C. similis appears to exhibit habitat restriction to lentic environments, primarily small brooks with depths typically less than 10 cm and puddles formed along edges of mountain valleys; (2) its habitats have relatively slow current velocities without exceeding 10.0 cm s–1; and (3) within brooks, bottom sediments typically consist of gravel (diameter 1–2 cm) and sand (diameter less than 2 mm), with this species predominantly found underneath rocks usually of diameter 10–30 cm. There is a method for investigating physical habitat characteristics of C. similis. It involves conducting experiments by manipulating only physical environmental conditions while keeping the water quality constant in a single stream. However, this approach presents challenges in obtaining a sufficient sample size for statistical analysis. It has limitations in obtaining meaningful statistical results for natural populations (Kong and Kim 2016). Therefore, in this study, physical habitat environmental factors measured at 58 survey sites where C. similis was present were used for HSI. Analysis results of HSI, mode values of C. similis habitat characteristics analyzed using the Weibull function were found to be 14.34 cm for water depth, 17.64 cm s–1 for current velocity, and –4.05 for substrate particle size (cobbly pebble). These results did not exhibit significant differences from habitat environment of C. similis previously described in the literature (Kawai and Min 2005). However, the main difference in this research was that the habitat of C. similis included both slow-flowing lotic environment and lentic habitats. This can be regarded as a mathematical validation of physical characteristics of habitats preferred by C. similis.

Shepard (1954) has classified sediments into 10 types using a triangular diagram based on composition ratios of sand, silt, and clay. Kong and Kim (2016) have applied this method and categorized streambed compositions into 10 levels. They proposed five substrate preferences for benthic habitats based on the average particle size: lithophilous (favoring large stones), psephophilous (favoring gravel), moderate, psammophilous (favoring sand), and pelophilous (favoring mud) types. After applying streambed characteristics of C. similis habitats measured in this study, results showed that the overall mean substrate was “cobbly pebble,” indicating a coarse particle-dominated characteristic for all 59 samples (Fig. 5, Table 6). In terms of streambed substate types, Psephophilous was the most dominant, accounting for 44.8% of the total, followed by Lithophilous at 36.8%, and Moderate at 18.4% in the assemblage composition. Kim et al. (2017) have classified microhabitats into nine types based on distribution characteristics of benthic macroinvertebrates according to water depth, current velocity, and substrate type in streams (Table 7). In this study, using the Weibull model, the median (depth of 19.58 cm, current velocity of 22.28 cm s–1, and substrate of –4.14) and mean (depth of 21.70 cm, current velocity of 24.22 cm s–1, and substrate of –4.17) values of environmental factors for C. similis were applied. As a result, all habitat types were classified as Run (VII) areas. Therefore, the stream current type of C. similis can be defined as a Run section with abundant coarse particle substate, low water depth, and slow water flow.

Table 6 . Number and percentage of sampling units, average of mean particle diameter and scheme of lithophilic series according to substrate types.

Revised from the article of Kong and Kim (J Korean Soc Water Environ. 2016;32(1):1-14).

Table 7 . Categorization of microhabitats based on composition rates of Habitat Orientation Groups according to habitat factors such as current velocity, water depth, and mean diameter of substrate.

Revised from the article of Kim et al. (J Korean Soc Water Environ. 2017;33(6):728-35).

Figure 5. Textural classification (A) and composition (B) of stream substrates in 58 sampling units of Cambaroides similis.

C. similis is designated as an endangered candiate species in South Korea. It is a species that requires continuous monitoring of population fluctuations for future decisions on whether to classify it as an endangered species. Opinions about the decline in the population size of C. similis have been raised since the 1970s (Jung et al. 2009). However, there is insufficient scientific evidence to support them. The decrease in freshwater crayfish population is not only a domestic issue but also a rapidly progressing problem worldwide, including Europe, North America, and Japan. It is known that this decline, coupled with global warming, is predicted to accelerate further (Nakata et al. 2002; Meyer et al. 2007). Factors threatening the survival of freshwater crayfish are known to be acidification (Appelberg 1986; France and Collins 1993), light pollution, water temperature (Reynolds 2002), hydrological changes (Contreras-Balderas and de Lourdes Lozano-Vilano 1996), habitat competition by invasive species, and the spread of fatal crayfish plague (A. astaci) infection (Jung et al. 2009). The pH range of most benthic macroinvertebrates habitats in streams is 6.5 to 8.5 (Dajoz 1975). According to study by Jung et al. (2009), the pH of C. similis habitat is around 6.4 on average, indicating that they can survive in slightly acidic environments. There is an opinion that the introduction of electricity near C. similis habitats can lead to disappearance of nocturnal C. similis. However, electricity might not be a direct cause of the decline in C. similis populations (Jung et al. 2009). Cambaroides similis is known to be a cold-water species. Nevertheless, it actually exhibits a faster growth in higher water temperatures (Jung et al. 2009). However, considering that mating behavior begins in September to October when water temperatures start to decrease, detailed studies on factors such as egg-laying rates related to the increase in water temperature would be necessary. Due to frequent droughts during the winter and early spring, C. similis populations may have drastically decreased or even disappeared (Ahn et al. 2011). Therefore, to conserve C. similis habitats, it is necessary to conduct research on ecological streamflow for C. similis habitats and develop management strategies accordingly. As a result, efforts are needed to maintain the minimum ecological flow required for the survival of C. similis in its habitats. The red swamp crayfish (Procambarus clarkii), an invasive species, is known to cause decline of C. similis populations through competition for habitat and food resources (Hernandez-Suarez and Nejadhashemi 2018) and by transmitting fungal disease A. astaci and white spot syndrome virus that can lead to extinction of competing species (Loureiro et al. 2015). The American crayfish (P. clarkii) is mainly distributed in the southern regions of South Korea, such as Jeollabuk-do, Chungcheongnam-do, and Gyeongsangnam-do. It is predicted that by 2050, its habitat range will expand even further to include Gyeongsangbuk-do and Incheon (Lee and Park 2019). To assess the impact of red swamp crayfish on the decline of C. similis populations, it is necessary to track long-term distribution changes of both species. Based on these threats, it is necessary to establish conservation strategies for protecting the population and habitat of C. similis by identifying and prioritizing threats through threat assessment.

Conclusions

Go to

• Abstract
• Introduction
• Materials and Methods
• Results
• Discussion
• Conclusions
• Acknowledgements
• Abbreviations
• Authors’ contributions
• Funding
• Availability of data|materials
• Ethics approval and consent to participate
• Consent for publication
• Competing interests
• References

Analysis of physical habitat characteristics of the designated endangered candidate species C. similis (Arthropoda, Decapoda) by the Ministry of Environment resulted in the following conclusions. This study identified physical microhabitat characteristics of C. similis as a Run section with coarse particle streambed substrate, low water depth, and slow current velocity in the stream. These results are significant as the first study to statistically validate physical habitat characteristics of C. similis. Furthermore, this study serves as the first nationwide investigation of C. similis habitats. Results of this study are expected to be utilized as fundamental data for future assessments of C. similis population fluctuations. Further research is needed to study impacts of identified threats, such as acidification, light pollution, water temperature, hydrology, habitat competition by invasive species, and spread of fatal crayfish plague (A. astaci) infection.

Acknowledgements

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• Abstract
• Introduction
• Materials and Methods
• Results
• Discussion
• Conclusions
• Acknowledgements
• Abbreviations
• Authors’ contributions
• Funding
• Availability of data|materials
• Ethics approval and consent to participate
• Consent for publication
• Competing interests
• References

Abbreviations

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• Abstract
• Introduction
• Materials and Methods
• Results
• Discussion
• Conclusions
• Acknowledgements
• Abbreviations
• Authors’ contributions
• Funding
• Availability of data|materials
• Ethics approval and consent to participate
• Consent for publication
• Competing interests
• References

CDF: Cumulative density function

CMF: Cumulative mass function

PDF: Probability density function

PMF: Probability mass function

HSI: Habitat suitability index

IFASG: Instream Flow and Aquatic Systems Group

NRMSE: Normalized root mean squared error

JYK did formal analysis, visualization and writing-original draft. YJK (Yong Ju Kwon), YJK (Ye Ji Kim), YDH, JSH, and CHA did data curation, and writing-review and editing. YSP did funding acquisition, project administration, resources, and writing-review and editing. DK did conceptualization, supervision, formal analysis, and writing-review and editing. All authors read and approved the final manuscript.

Funding

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• Abstract
• Introduction
• Materials and Methods
• Results
• Discussion
• Conclusions
• Acknowledgements
• Abbreviations
• Authors’ contributions
• Funding
• Availability of data|materials
• Ethics approval and consent to participate
• Consent for publication
• Competing interests
• References

This study was supported by ‘survey on endangered candidate species (NIE-Outsourced Research-2023-103)’ funded by the Ministry of Environment.

The datasets used and/or analyzed during the current study are available from the corresponding author on reasonable request.

References

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• Abstract
• Introduction
• Materials and Methods
• Results
• Discussion
• Conclusions
• Acknowledgements
• Abbreviations
• Authors’ contributions
• Funding
• Availability of data|materials
• Ethics approval and consent to participate
• Consent for publication
• Competing interests
• References

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