Climate-Driven Oceanographic Changes Shape Larval Dispersal Success in the Southern Ocean

Although climate-driven changes in ocean circulation are increasingly recognized as key drivers of marine ecosystem structure and dynamics, their consequences for the early life stages of deep-sea fishes remain difficult to quantify. In the Southern Ocean, variability in frontal systems such as the Polar Front (PF) may influence larval dispersal and retention, with direct implications for recruitment. We investigated how interannual variability in ocean circulation and egg production shapes larval dispersal and retention in suitable recruitment areas of a large body size deep-sea fish species, Patagonian toothfish (Dissostichus eleginoides), around the Kerguelen Plateau. We developed an integrated modeling framework which combined spatially explicit models of egg production with 24 years (2000-2023) of Lagrangian dispersal simulations driven by satellite-derived geostrophic currents to quantify successful larval retention. Ontogenetic changes in distribution and fecundity were accounted for to model egg production, allowing retention metrics to reflect spatial heterogeneity in reproductive output. Larval retention rate in suitable recruitment areas varied from 9% to 28% over the study period. PF-associated jet intensity was significantly associated with larval retention variability: years characterized by stronger PF-associated circulation showed lower larval retention, with more larvae advected away from the shelf toward the eastern part of the plateau. The latter part of the time series, particularly after 2010, was characterized by stronger year-to-year fluctuations, a higher contribution of the North-West recruitment area, and more frequent low-retention years. Building on new findings on toothfish spawning dynamics and long-term altimetry data, we showed for the first time that there is the potential for self-recruitment in the northern part of the Kerguelen Plateau (French EEZ). We also discussed the implications for fishery management since PF-associated indices may help interpret past recruitment trends and offer useful early-warning for future recruitment anomalies.