Iori Mizukami

Aim: Poleward range extensions of marine fishes under climate change are increasingly being reported around the world, but tracking northern latitudinal limits of fish species remains challenging. Occurrence data accumulated from eDNA surveys in Japan could be utilized to detect out‐of‐range occurrences and track cool leading range edges as fish species shift in response to climate change and other anthropogenic impacts into the future. Location: Japan EEZ coastlines. Methods: We analysed a large environmental DNA (eDNA) dataset (2904 marine eDNA samples; 36,247 occurrences for 1290 fish species; 2017–2024) from across Japan, obtained from sampling surveys we conducted along the Eastern Pacific coastlines of Japan and the sequencing datasets on the All Nippon eDNA Monitoring Network (ANEMONE) database, and assessed the latitudinal novelty of the northernmost eDNA occurrence records of species in comparison to existing biogeographical data from three data infrastructures: (1) GBIF/OBIS occurrence records, (2) Aquamaps modelled core habitats, and (3) IUCN expert range maps. Results: Our analysis identified 126 fish species with eDNA northern limits significantly beyond what is reported by the three reference datasets, including subtropical vagrants potentially overwintering, commercially important species, and small cryptic species. eDNA detected high annual numbers of out‐of‐range occurrences (maximum 511 vs. IUCN, 1069 vs. Aquamaps) across sampling‐intensive years (2020–2022), greater than what is available on GBIF‐OBIS, thus complementing traditional methods with improved scalability for distribution range characterization and tracking range edges. Main Conclusions: This work underscores eDNA's long‐term utility in tracking species redistributions. eDNA occurrence data can fill in the gaps in biogeographical knowledge with its improved scalability for distribution range characterization and tracking range edges. Discrepancies across reference data sources highlight the need for their harmonization and cross‐referencing to literature prior to their use as baselines.

Three genera of the family Onchidiidae, Peronia, Wallaconchis and Onchidella, are known to inhabit intertidal coral reef environments in the Ryukyu Islands, however, there have been only limited studies on their diversity. This study conducted surveys around 11 islands and 40 intertidal areas of the Ryukyus, elucidating species diversity utilizing DNA barcoding of specimens. Molecular data indicated that intertidal coral reef areas of the Ryukyu Islands harbor at least eight Onchidiidae species from three genera. The highest species cohabitation in the same intertidal areas was observed around Okinawa-jima Island; five species from three genera. Peronia spp. were found from all sites investigated in this study and the distribution ranges of four species of Peronia in the Ryukyu Islands were updated from past research. Three species of Wallaconchis; W. ater, W. nangkauriensis, and Wallaconchis sp., were found in intertidal coral reef environments, mostly in flat areas with small rubble and rocks. Onchidella sp. inhabited intertidal areas and was found on many more islands of the Ryukyus than previously had been documented. All Onchidella sp. specimens collected from the Ryukyus were genetically distinct from described species. This study enhances the understanding of Onchidiidae diversity in intertidal coral reef environments of the Ryukyu Islands, providing a baseline dataset for better conservation of this understudied group.

The association between two hydrozoans, Stylaster sp. and Millepora spp., has been described as a case of pseudo-auto-epizoism, and has only been reported from the Caribbean region of the Atlantic Ocean. Here, we report on the occurrence of this association in the Pacific Ocean on coral reefs around Iriomote-jima Island, Japan, suggesting the association to be more widespread than had previously been thought. Moreover, Stylaster sp. colonies were observed living healthily on bleached and dead branches of Millepora spp., indicating that this interaction is facultative. The interaction reported here differs from the relationship between the Caribbean Stylaster roseus and Millepora alcicornis by the connection points between the two partners, which is made evident by the whitening of the Millepora counterpart in Iriomote-jima Island, while being seamless in the Caribbean association. Further research is necessary to fully understand the nature of these relationships, comprehending under what conditions it occurs, and establishing which species are involved in the interactions.

Species of the genus Peronia Fleming, 1822, are air-breathing onchidiid sea slugs that inhabit intertidal reef flats of temperate to tropical zones. In the Ryukyu Islands of southern subtropical Japan, Peronia species are a traditional food source for local people. To date, there have been three species recorded around Okinawajima Island; P. verruculata and P. peronii, along with recently described P. okinawensis, which was described as possibly endemic to Okinawajima Island. This study aimed to map the distribution ranges of these three Peronia species within the Ryukyu Islands using molecular analyses in order to understand the specific distribution of each species. Since Peronia species are generally indistinguishable by gross external morphology, a DNA barcoding approach was employed to identify specimens. The molecular data showed that there are four species present in the Ryukyu Islands. P. verruculata (unit #1 sensu Dayrat et al., 2020) was dominant at almost all locations, while P. peronii was present in much lower numbers than P. verruculata, but found across a relatively wide range in the Ryukyu Islands. We newly record P. okinawensis and P. setoensis from Amami Oshima Island and from several places around Okinawajima Island, and also identified high levels of genetic variation within P. setoensis. Peronia okinawensis and P. setoensis have been thought to be endemic to Okinawajima Island and to Honshu, mainland Japan, respectively. However, as both species were observed around Okinawajima and Amami Oshima islands, other islands of the Ryukyus are also likely to harbor these species, and their distribution ranges are wider than previously thought. Based on the results from molecular analyses, we provide general descriptions of each species. Sizes of specimens were consistently smaller for P. setoensis and relatively larger for P. peronii specimens. On the other hand, P. verruculata and P. okinawensis had similar size ranges, but P. okinawensis had comparatively much more distinct papillae. This study revealed that the Ryukyu Islands are the only region currently known with four sympatric Peronia species, and this work provides a basis for future research on these Peronia species throughout the northwest Pacific Ocean, representing the first step in more effective management of the local Peronia fisheries in the Ryukyu Islands.