The Eastern Pacific Barrier (EPB), a vast expanse of deep ocean between the central and eastern Pacific, has been considered an almost insurmountable obstacle to larval dispersal since the time of Darwin and Ekman. The central Pacific west of the barrier is rich in coral species (more than 100), while the eastern tropical Pacific to its east is poor (only three dominant reef-building species). Genetic analysis of the reef-building coral Porites lobata shows very weak gene flow across the barrier, but Clipperton Atoll on the eastern side is an exception: its samples are genetically linked to the Line Islands in the west. This contradicts the prevailing westward circulation of equatorial currents, where the only eastward transport mechanism is the surface North Equatorial Countercurrent (NECC). This work stands apart: the closest neighbor in the archive is the Hubbard model, but direct observational studies linking circulation to coral genetics across the EPB have been lacking.
The authors used 26,624 trajectories from satellite-tracked drifting buoys of the Global Drifter Program (GDP) from 1979 to 2025, selecting only periods when the underwater drogue was attached, ensuring the motion reflects passive larval transport. Trajectories were discretized into a Markov chain with a 5-day time step on a grid of 103 Voronoi cells obtained by k-means clustering of buoy coordinates. They applied transition path theory (TPT), which identifies reactive trajectories: paths from a source (islands west of the EPB) to a target (islands to the east) with minimal deviations, and Bayesian inversion to estimate the likely origin of larvae reaching Clipperton. Seasonal and interannual variability were tested by building separate chains for summer–autumn and winter–spring months, as well as for El Niño and La Niña phases based on the ONI index.
Reactive currents revealed a distinct pathway from the Line Islands (LN cells) to Clipperton Atoll (CL cell), which sharply decays near the target. The time to reach the target (the remaining duration of reactive trajectories) for this pathway does not exceed 5 months, matching the upper limit of P. lobata larval survival, and the Bayesian inversion gives a local maximum transfer probability at about 2.5 months. The connection to the Hawaiian Islands proved biologically unfeasible: travel times are substantially longer than 5 months due to delays in the Great Pacific Garbage Patch region. Seasonal analysis showed that the reactive current between the Line Islands and Clipperton exists in summer and autumn but disappears in winter and spring, consistent with the seasonal strengthening of the NECC. The influence of ENSO phases was weak: the current during El Niño is comparable to neutral conditions, while during La Niña the connection to Hawaii is an order of magnitude weaker.
This work is the first to link observed circulation with genetic data through a rigorous probabilistic framework, unlike neighboring studies that either relied on numerical models or examined individual trajectories. It shows that the EPB is not a static barrier: it should be defined through the statistics of remaining reactive trajectory duration, not as a fixed geographic line. This shifts the focus from biological assumptions to physical dynamics and provides a quantitative tool for assessing rare but evolutionarily significant transport events.
The proposed method can be extended to other species with different larval durations and to other regions with hypothesized biogeographic barriers. Refining the TPT-based definition of the EPB can be tested with new genetic samples, especially in areas with short travel times. Incorporating vertical current structure and larval behavior (vertical migrations) will improve the realism of transport models.
The results are important for marine biogeography, management of protected areas, and assessing coral population connectivity under climate change. The role of Clipperton Atoll as a sink for trajectories has direct relevance to the planned deep-sea mining of polymetallic nodules in the Clarion-Clipperton Zone.
Test TPT predictions with new genetic data from locations with short travel times, such as near Clipperton Atoll. Investigate the influence of larval vertical behavior on transport pathways by adding data on deep circulation.
This work directly addresses the unresolved problem of quantifying marine population connectivity across oceanic barriers, where classical views of impermeability conflict with genetic observations. It offers a dynamic barrier definition applicable to other species and regions, but the question remains how universal such pathways are for different taxa with varying larval biology.
Clipperton Atoll, an uninhabited coral island in the eastern Pacific, turns out to be a genetic bridge between the central and eastern Pacific, despite being thousands of kilometers from other reefs.