First record of Macrobrachium australe (Guérin-Méneville, 1838) (Crustacea, Decapoda, Palaemonidae) from Ogasawara (Bonin) Islands, an oceanic island group of Japan

the journal of biodiversity data NOTES ON GEOGRAPHIC DISTRIBUTION 1231 Academic editor: Gianna Innocenti Received: 27 October 2025 Accepted: 8 December 2025 Published: 16 December 2025 Copyright © The authors. This is an open‑access article distributed under terms of the Creative Commons Attribution License (Attribution 4.0 International – CC BY 4.0) Abstract. The Ogasawara (Bonin) Islands are an oceanic island group and World Natural Heritage site in Japan. This study reports the first record of the freshwater prawn Macrobrachium australe (Guérin-Méneville, 1838) on Chichi Island in the Ogasawara Islands. Although this amphidromous species has high dispersal ability, our comprehensive surveys across the islands found only one individual, with no evidence of establishment or reproduction. This case study of the accidental dispersal of amphidromous species to oceanic islands is significant from a biogeographical perspective. Key words. Amphidromous, biogeography, DNA barcoding, mitochondrial DNA Hanai M, Fuke Y (2025) First record of Macrobrachium australe (Guérin-Méneville, 1838) (Crustacea, Decapoda, Palaemonidae) from Ogasawara (Bonin) Islands, an oceanic island group of Japan. Check List 21 (6): 1231–1237. https://doi.org/10.15560/21.6.1231 Introduction Infrequent colonization events and subsequent adaptive evolution have shaped unique ecosystems on oceanic islands that have never been connected to a continent. Consequently, oceanic islands are widely regarded as model systems for investigating the processes and mechanisms of community formation (Whittaker et al. 2008; Shaw and Gillespie 2016). However, most previous studies have focused on terrestrial and marine ecosystems, and our knowledge of freshwater biotic community formation on oceanic islands remains limited (McDowall 2003). Macrobrachium Spence Bate, 1868 is a large genus of freshwater and brackish-water prawns that are widely distributed in temperate and tropical regions worldwide, comprising approximately 280 species (DecaNet Eds. 2025). Eighteen species have been reported in Japan, 17 of which have an amphidromous life history, spending their larval stages in brackish water or seawater (Shokita 2019; Fuke and Maruyama 2023). Such amphidromous species are presumed to possess a high dispersal ability via ocean currents (Iida et al. 2010; Anger 2013). The number of species capable of reaching highly isolated oceanic islands is believed to be limited by the length of their planktonic larval stage (McDowall 2003; Fuke and Sasazuka 2021). The genus Macrobrachium represents a suitable taxon for examining these processes, and its species diversity on oceanic islands needs to be clarified. This study reports the first record of Macrobrachium australe (Guérin-Méneville, 1838) on the Ogasawara (Bonin) Islands, an oceanic island group in Japan. This finding is important for understanding the regional freshwater fauna of the Ogasawara Islands. Study area The Ogasawara Islands are a subtropical archipelago in the Pacific Ocean located approximately 1,000 km south of mainland Japan (Figure 1). Adaptive radiation has repeatedly occurred among the plants and land snails of the Ogasawara Islands (Ito 1998; Chiba and Cowie 2016), making them important 21 (6) · https://doi.org/10.15560/21.6.1231 21 (6): 1231–1237. https://doi.org/10.15560/21.6.1231 First record of Macrobrachium australe (Guérin-Méneville, 1838) (Crustacea, Decapoda, Palaemonidae) from Ogasawara (Bonin) Islands, an oceanic island group of Japan Motoya Hanai1, Yusuke Fuke2 1 Graduate School of Marine Science and Technology, Tokyo University of Marine Science and Technology, Minato, Tokyo, Japan 2 Division of Applied Biological Science, Faculty of Agriculture, Setsunan University, Hirakata, Osaka, Japan The authors have contributed equally to this manuscript. Corresponding author: Yusuke Fuke ([email protected]) Check List 21 (6) · https://doi.org/10.15560/21.6.1231 Hanai and Fuke · Macrobrachium australe from Ogasawara Islands 1232 natural laboratories for studying evolution. Furthermore, rare colonization from various regions and subsequent adaptive evolution have been documented across a wide range of taxa (e.g. Noda et al. 2022; Tomikawa et al. 2022, 2023; Tsujimoto et al. 2023; Nishimura and Takayama 2025; Souma 2025). The value of these ecosystems has been recognized, leading to their designation as a UNESCO World Heritage Site and a national park. The freshwater habitats of the islands also harbour several endemic species (Satake et al. 2019), although research on these habitats remains limited compared to that on terrestrial ecosystems. Eight species of freshwater shrimp have been reported on the Ogasawara Islands (Table 1; Fuke et al. 2025; Fuke and Sasaki 2025). Among these eight species, Palaemon ogasawaraensis Kato & Takeda, 1981 and Paratya boninensis Satake & Cai, 2005 are endemic to the Ogasawara Islands, whereas the remaining six species are widely distributed. Methods Thirty-one surveys in the Ogasawara Islands were conducted between March 2022 and August 2025, covering 11 river systems on the Chichi and Haha islands (Figure 2). Access to national forests was granted after completion of the Ogasawara Islands Forest Ecosystem Conservation Area Usage Figure 1. Distribution maps of Macrobrachium australe. A. World map. The red line indicates the distribution range of this species. B. Detailed map around Japan. Red points and fills represent the occurrence of this species in Japan. 500 km Kuroshio Current Ryukyu Islands Honshu Shikoku Kyushu Ogasawara Islands Chichi Island Haha Island N 2000 km N 30° N 30°S 120°E90°E60°E 150°E 180° 150°W 0° A B B 30° N 130°E120°E 140°E Check List 21 (6) · https://doi.org/10.15560/21.6.1231 Hanai and Fuke · Macrobrachium australe from Ogasawara Islands 1233 course. The collected specimen was preserved in 100% ethanol onsite and deposited at the Zoological Collection of Kyoto University (KUZ). To assess the morphological characteristics of the specimen, the postorbital carapace length (CL) was measured after preservation using digital callipers. Total DNA was extracted from the fifth pleopod using the Monarch Spin gDNA Extraction Kit (New England Biolabs). A partial mitochondrial 16S rRNA gene was amplified using PCR with the primer pairs 16S-F1 (5′-GTA CCT TTT GTA TCA GGG-3′) and 16S-R1 (5′-CGG TYT GAA CTC AAA TCA TG-3′) (Fuke and Maruyama 2023). The composition of the 12 μL PCR reaction mixture was as follows: 6.0 μL of 2×PrimeSTAR GXL Premix Fast (TaKaRa, Japan), 0.7 μL of each 5 μM primer, 0.8 μL of template DNA, and 3.8 μL of ultrapure water. The PCR amplification conditions were as follows: initial denaturation (98°C, 10 s); 30 cycles of denaturation (98°C, 10 s), annealing (55°C, 5 s), and extension (68°C, 5 s); and a single final extension (68°C, 10 s). The PCR product was purified using ExoSAP-IT Express (Applied Biosystems, USA) and outsourced to Macrogen, Japan, for Sanger sequencing. The obtained sequence was checked for quality and was manually edited using Unipro UGENE 51.0 (Okonechnikov et al. 2012). For DNA barcoding, similarity search of the nucleotide sequence was performed using BLAST (Johnson et al. 2008) with default settings. The sequence was deposited in the International Nucleotide Sequence Database via the DDBJ (accession number: LC897214). The maps were created using QGIS 3.40 (QGIS.org 2025). The GIS data were sourced from publicly available datasets provided by MLIT of Japan (2024) and Natural Earth (2024). Results Order Decapoda Family Palaemonidae Rafinesque, 1815 Genus Macrobrachium Spence Bate, 1868 Macrobrachium australe (Guérin-Méneville, 1838) Figure 2C Materials examined. JAPAN — Tokyo • Ogasawara (Bonin) Islands, Chichi Island, Stream of Kopepe Beach; 27°03’54.1”N 142°11’37.5”E; 31 Mar. 2022; Motoya Hanai leg.; DNA accession number: LC897214; 1♀, CL 6.97 mm, KUZ Z6318. Identification. The examined specimen was identified by DNA barcoding, and its morphological characteristics also supported this identification. A similarity search using mtDNA 16S rRNA (970 bp) showed that the individual obtained from the Ogasawara Islands matched M. australe, identified based on morphological traits (Castelin et al. 2017; Fuke and Imai 2018), at 100% (Table 2). Because the examined specimen was female and immature, the morphology of the second pleopod was not examined. The rostrum is slender and upcurved, with its tip extending beyond the end of the scaphocerite. The rostrum tooth formula was 3+6+2/5. The specimen exhibited three red bands on the lateral surface of the carapace in its fresh condition. These characteristics are consistent with those of M. australe (Holthuis 1950; Castelin et al. 2017). Distribution. Macrobrachium australe has been reported to occur from the Indian Ocean to the Central Pacific Ocean (Figure 1A; Holthuis 1950; Ito et al. 2002; Chen et al. 2009; Castelin et al. 2017). In Japan, this species has been recorded in Honshu (Imai et al. 2008; Kitano and Terada 2015; Maruyama 2017, 2018), Shikoku (Imai et al. 2015), Kyushu (Suzuki et al. 1993; Imai and Nakaso 2019; Imai and Oonuki 2023), and the Ryukyu Islands (Shokita 2019; Fuke and Imai 2018) (Figure 1B). Among these, stable Table 1. List of freshwater shrimps in Ogasawara (Bonin) Islands, Japan. Family Species Life history type Note References Palaemonidae Macrobrachium australe (Guérin-Méneville, 1838) Amphidromous This study Palaemonidae Macrobrachium japonicum (De Haan, 1849) Amphidromous Fuke et al. 2025 Palaemonidae Macrobrachium lar (Fabricius, 1798) Amphidromous Yoshigou 2002 Palaemonidae Palaemon ogasawaraensis Kato & Takeda, 1981 Amphidromous Type locality, endemic Kato and Takeda 1981 Atyidae Atyoida pilipes (Newport, 1847) Amphidromous Cai et al. 2006 Atyidae Caridina multidentata Stimpson, 1860 Amphidromous Type locality Cai et al. 2006 Atyidae Caridina serratirostris De Man, 1892 Amphidromous Fuke and Sasaki 2025 Atyidae Caridina typus H. Milne Edwards, 1837 Amphidromous Cai et al. 2006 Atyidae Paratya boninensis Satake & Cai, 2005 Land-locked Type locality, endemic Satake and Cai 2005 Check List 21 (6) · https://doi.org/10.15560/21.6.1231 Hanai and Fuke · Macrobrachium australe from Ogasawara Islands 1234 establishment and reproduction have only been confirmed in a few rivers in Honshu, with year-round high-water temperatures due to warm wastewater and hot springs, and in the Ryukyu Islands. Habitat. Macrobrachium australe was confirmed in a single individual from a small stream draining into Kopepe Beach on Chichi Island (Figure 2A, D). In the Ryukyu Islands, this species typically occurs in stagnant water environments in the lower to middle reaches of small streams (Shokita 1975; Fuke et al. 2024), and in the Ogasawara Islands, the species was likewise found in a similar habitat. Discussion We report the first record of Macrobrachium australe in the Ogasawara Islands. As this species is not commonly available in the Japanese pet trade and no other non-native freshwater crustaceans have been documented in the region, the collected specimen is considered to be of natural origin rather than introduced. The specimen was immature, indicating that recruitment occurred recently. Our study successfully documents accidental dispersal, which is generally difficult to observe despite its importance, and thus provides valuable biogeographical insights on oceanic islands. Accidental dispersal is a crucial initial step in the formation of regional biota and speciation (Heaney 2000; Whittaker et al. 2008, 2017). Despite our comprehensive survey and previous surveys of the Ogasawara Islands, only a single individual was recorded, and no evidence of establishment or reproduction in Figure 2. Survey sites in the Ogasawara Islands with photographs of the specimen and its habitat. Numbers following river names indicate the number of surveys conducted. Dates in gray represent survey dates, and dates in bold indicate when the species was collected. A. Chichi Island. B. Haha Island. C. Macrobrachium australe collected from Chichi Island. D. Habitat, small stream of Kopepe Beach, Chichi Island. Table 2. BLAST search results for Macrobrachium australe collected Ogasawara Islands based on partial mtDNA 16S rRNA. Only the top 10 hits were shown. Query sample Hit species Length (bp) Query cover Identity Accession Reference KUZ Z6318 LC897214 Macrobrachium australe 509 50% 100% KY039501.1 Castelin et al. 2017 Macrobrachium australe 509 50% 100% KY039513.1 Castelin et al. 2017 Macrobrachium australe 509 50% 100% KY039517.1 Castelin et al. 2017 Macrobrachium australe 507 48% 100% LC366024.1 Fuke and Imai 2018 Macrobrachium australe 472 47% 100% LC316193.1 Fuke and Imai 2018 Macrobrachium australe 472 47% 100% LC316195.1 Fuke and Imai 2018 Macrobrachium australe 472 47% 100% LC316196.1 Fuke and Imai 2018 Macrobrachium australe 472 47% 100% LC316197.1 Fuke and Imai 2018 Macrobrachium australe 472 47% 100% LC316201.1 Fuke and Imai 2018 Macrobrachium australe 472 47% 100% LC316203.1 Fuke and Imai 2018 Check List 21 (6) · https://doi.org/10.15560/21.6.1231 Hanai and Fuke · Macrobrachium australe from Ogasawara Islands 1235 the region was obtained (Fuke et al. 2025). Although the complete zoeal stage of this species remains unclear, it is known to have a planktonic larval period of at least 50–147 days (Ito et al. 2002). Given its wide distribution range, this species possesses a high dispersal ability. This suggests that even species with high dispersal ability, such as M. australe, rarely reach the Ogasawara Islands. The processes and mechanisms underlying the community formation of freshwater crustaceans on the Ogasawara Islands remain unresolved. Eight shrimp species, excluding M. australe, are reliably known to occur in this region (Fuke et al. 2025). However, it remains unclear whether the Ogasawara populations of these species are genetically isolated from those of other regions or whether they maintain gene flow. Macrobrachium lar (Fabricius, 1798) have relatively long planktonic larval stages (77–110 days; Lal et al. 2014), suggesting that they may maintain gene flow to other regions, as demonstrated by M. australe in this study. In contrast, whether the Ogasawara populations of other widely distributed species, such as M. japonicum (De Haan, 1849) (42–47 days; Morizane and Minamizawa 1971), Caridina typus H. Milne Edwards, 1837 (22–44 days; Nakahara et al. 2005), C. multidentata Stimpson, 1860 (26–49 days; Hayashi and Hamano 1984), and C. serratirostris De Man, 1892 (34–46 days; Nakahara et al. 2005) are isolated or connected through gene flow requires further examination using phylogeographic approaches. No information is available regarding the complete larval stages of Atyoida pilipes (Newport, 1847), Pal. ogasawaraensis, and Par. boninensis, highlighting the need to accumulate fundamental knowledge of their early life histories. In the future, a detailed examination of the migration patterns and gene flow from other regions may provide important insights into the origin of freshwater biodiversity on oceanic islands. Acknowledgements We are grateful to Tetsuro Sasaki (IBO), Chika Sato (Ministry of the Environment; ME), and Nayuta Yamamoto (ME) for supporting the fieldwork, and members of the Ogasawara Ranger Office, ME and National Forest Section, Forestry Agency, for supporting the approval of the survey permit. Additional information Conflict of interest The authors declare that no competing interests exist. Ethical statement No ethical statement is reported. Funding This study was supported by JSPS KAKENHI (grant number JP23KJ2156). Author contributions Conceptualization: MH. Investigation: MH, YF. Data curation and formal analysis: YF. Writing – original draft: YF. Writing – review and editing: MH, YF. Author ORCID iDs Motoya Hanai https://orcid.org/0009-0000-0379-3438 Yusuke Fuke https://orcid.org/0000-0001-6404-6241 Data availability The collected specimen was deposited in the Zoological Collection of Kyoto University (KUZ Z6318). 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