Roles of vertical behavior in the open-ocean migration of teleplanic larvae: a modeling approach to the larval transport of Japanese spiny lobster

The vertical behavior of planktonic larvae has been increasingly recognized as an important factor in their transport. However, little is known about the roles of this behavior in openocean migration of teleplanic larvae. Using Japanese spiny lobster Panulirus japonicus in the western North Pacific and adjacent waters as a model species, we aimed to clarify (1) the effect of vertical behavior of larvae on transport success, (2) migration pathways of larvae, and (3) mechanisms that enable larvae to approach adult habitats before metamorphosing into competent swimmers (pueruli). Larval transport was simulated using an individual-based model with 10 different vertical behavior types (VBTs) and mortality caused by exposure to water temperatures outside the range (19–30°C) at which wild larvae appear. The VBTs that started transport at a shallow depth (1 m) had significantly higher transport success than those that started at greater depths (≥25 m). Of the successful VBTs, those with ontogenetic vertical migration (OVM) showed greater detrainment of particles from the Kuroshio Extension (KE) and facilitated southwestward transport of particles in the re cir culation region. Furthermore, the results indicate that phyllosoma larvae are transported by the Kuroshio, KE, and Kuroshio Countercurrent. Our study suggested that (1) detrainment of phyllosoma larvae from the KE to the recirculation region is facilitated by OVM and cross-frontal exchange at the meander trough, and (2) southwestward transport to adult habitats and avoidance of the low-temperature water shifting southward in winter are facilitated by OVM and the beta spiral. These findings highlight the importance of vertical behavior in open-ocean migration of teleplanic larvae.