Shin-Ichi Ito

Marine ecosystems exhibit high spatiotemporal heterogeneity, making it crucial to understand the mechanisms sustaining biological hotspots. Ocean fronts shape local biogeochemical processes and have long been recognized as biological hotspots aggregating organisms from phytoplankton to top predators and attracting fisheries (hotspot effects). However, fronts also exhibit pronounced environmental differences between their two sides (barrier effects), and how species and fishery distributions respond to these effects remains poorly understood. By integrating satellite-based front detection with commercial catch records, fishery-independent surveys, and global fishing datasets, we show that fishery distributions across diverse regions and major commercial stocks worldwide respond strongly to barrier effects, exhibiting 15–70% differences in distribution between the frontal warm and cold zones, driven by species-specific local thermal preferences. In contrast, responses to hotspot effects are generally sporadic with only 5–20% differences between frontal and non-frontal zones, and they emerge only when aggregations on one side of fronts offset avoidance on the other. This offset has led earlier studies to conservatively underestimate front-induced fishery variations by 55–75%. Our findings complement the traditional front-induced hotspot paradigm by clarifying the importance of barrier effects and underscore the need to reassess the role of ocean fronts in marine ecosystems.

Global oceans have warmed markedly and will continue to do so. Superimposed on this trend are abrupt, persistent decadal regime shifts between warm and cold phases that alter ocean–atmosphere dynamics and reshape ecosystem composition and function. Despite recognition of the increasing risk of irreversible climate tipping points, the past and future evolution of these decadal warm–cold shifts remains unclear. Here, combining observations and simulations, we show a widespread 130–140% increase in the frequency and amplitude of sea surface temperature regime shifts across global Large Marine Ecosystems over the past 150 years, with asymmetries stronger in the Northern Hemisphere. Climate models attribute these trends to anthropogenic warming, which suppresses cold-regime transitions and reinforces warm regimes. Without mitigation, these shifts are projected to rise 130–180% by the late-21st century relative to recent levels, whereas only the lowest-emission scenario could constrain their intensification—except in the Arctic oceans. Further analyses reveal close links between intensified temperature regime shifts and abrupt ecological and fishery changes, showing 21–46% synchrony that is rising, potentially amplifying decadal ecosystem instability and socio economic challenges. From a marine perspective, these findings underscore the urgency of achieving the Paris Agreement’s target and the Arctic’s marked vulnerability.

Marine environmental DNA (eDNA) metabarcoding data are beginning to accumulate, even for remote and poorly studied areas, such as marine environments. These data enable us to identify distributions of target organisms and then to compare biological compositions between different marine areas. However, there is no platform to effectively utilise and accumulate these data. In this study, we developed eDNAmap, a web‐based platform designed to analyse and store marine eDNA metabarcoding data. By uploading species or sequence composition data with location information, eDNAmap users can automatically (1) plot sampling locations on a map, (2) generate a heatmap to evaluate potential batch effects arising from methodological differences and (3) perform nonmetric multidimensional scaling and cluster analyses using similarity indices. Furthermore, users can specify scientific names to display species distributions and upload species lists to assess species compositions of the target sea area. As an example, fish sequence composition data obtained from 55 stations around the Watase line—believed to exist along a geographic canyon known as the Tokara Gap—were used to verify its existence using eDNAmap. The platform includes a database primarily consisting of teleost fish data from the Northwestern Pacific, which users can analyse similarly to their own uploads. Although originally designed for fish, eDNAmap is flexible enough to handle data from other marine organisms. Analysing multiple taxa enables the detection of concordant biogeographic patterns across different groups, which can strengthen ecological interpretations and lay the groundwork for identifying environmental drivers shaping community structures. eDNAmap is available at https://github.com/jun‐inoue/eDNAmap .

Understanding marine surface fish diversity is crucial for ecosystem management. However, the traditional sampling methods are often invasive, costly, or unsuitable for certain species or locations. Environmental DNA (eDNA) metabarcoding provides a non-invasive and relatively cheap alternative to explore patterns of diversity. It is important to recognize that, eDNA-based inference can vary across sampling methods, potentially impacting the validity of biodiversity assessments. To evaluate and compare the effectiveness of three eDNA sampling methods—ship-bottom intake (4.5 m), Niskin bottles (5 or 10 m), and bucket (0 m)—for assessing fish diversity and fish community composition in the western North Pacific near Japan, we analyzed fish communities from 83 stations sampled during nine research cruises. Taxonomic analysis revealed that each method detected over 324 taxa, contributing to a total of 465 taxa. Hierarchical clustering generally identified similar species composition across methods at a station. The exception was when intake samples, collected at different times, diverged from bucket and Niskin samples at the same station. Hill’s number rarefaction and extrapolation curves across all clusters showed similar results among methods, with exceptions in a few clusters where bucket samples exhibited higher biodiversity indices than intake and Niskin samples. Non-metric multidimensional scaling indicated significant relationships between cluster composition and environmental factors like temperature, salinity, and chlorophyll-a. Some clusters were also controlled by integrated seasonal factors. Overall, fish community composition was convincingly similar among methods. This finding suggests that any of these eDNA sampling methods can be effective and may be prioritized based on logistical considerations.