Resilient Seas: Environmental Drivers of Larval Fish Assemblages in the Gulf of Tortugas, Colombian Pacific.

Nursery habitats sustain fish populations by supporting early life stages and buffering environmental variability, yet their functioning under climate oscillations remains poorly understood in the Eastern Tropical Pacific. We analyzed ichthyoplankton assemblages in the Gulf of Tortugas, Colombia (2010-2020), to assess taxonomic composition, spatiotemporal variability, and environmental drivers. ENSO cycles and local oceanographic conditions were evaluated as determinants of nursery function and resilience using richness estimators, diversity indices, Caswell's neutral model, and multivariate approaches (PERMANOVA, PERMDISP, CAP, BIOENV). Assemblages were dominated by Cetengraulis mysticetus, with recurrent contributions from Sciaenidae, Haemulidae, Gerreidae, and Carangidae-families of artisanal fisheries importance. ENSO phases explained interannual variability: El Niño years reduced diversity and weakened retention, whereas La Niña years supported more balanced assemblages. Spatial heterogeneity revealed central retention zones and peripheral diversity hotspots. Environmental gradients, particularly chlorophyll-a, zooplankton biomass, transparency, and pH, consistently structured larval distribution, reflecting the coupling of productivity, water quality, and circulation. These findings demonstrate that the Gulf of Tortugas functions as a dual nursery system and ecological node of resilience, underscoring the importance of protecting such habitats for ecosystem-based fisheries management and biodiversity conservation in a changing ocean.