Spatio-temporal variability in medusa biomass linked to oceanographic conditions in a productive shelf ecosystem of the Southwestern Atlantic

This study presents the first large-scale, long-term ecological assessment of a large pelagic cnidarian (Aequorea forskalea) within a highly productive and economically significant marine area of the Southwestern Atlantic. Using nearly three decades of summer fishery survey data (1995–2024), we evaluated the spatial and temporal variability of Aequorea biomass and its relationship with oceanographic conditions. Biomass distribution was spatially structured, concentrating in the San Jorge Gulf, a temporally persistent hotspot of biomass. A major shift in biomass occurred in 2011, marking a transition from a high-biomass phase (1995–2010) to a period of low biomass (2011–2024), coinciding with rising bottom temperatures and decreasing salinity in hotspot areas. Given the spatio-temporal overlap with early life stages of key fisheries species (Argentine hake and Patagonian red shrimp), Aequorea may influence recruitment dynamics through predation and competition. These findings underscore the importance of integrating biological and physical data to understand gelatinous zooplankton dynamics. Long-term fisheries surveys are shown to be valuable sources of baseline data, essential for predicting ecosystem responses to environmental change.