Shifting Seas, Changing Diets: Evidence of Temporal Dietary Shifts in Marine Megafauna in Southern Brazil (2017–2023)

ABSTRACT Understanding the dietary dynamics of marine megafauna is essential for interpreting ecological interactions and assessing environmental changes in marine ecosystems. We analysed temporal trends in the diets of eight megafaunal species, comprising marine mammals, seabirds, and sea turtles. The study was based on gut content data from stranded individuals along the Paraná coastline (southern Brazil) between 2017 and 2023. Using a combination of species richness estimators and Canonical Analysis of Principal Coordinates (CAP), we assessed changes in prey diversity and composition over time. A total of 50 prey items were identified, including teleost fishes, cephalopods, macroalgae, and vascular plants. While all species showed evidence of dietary variation, significant temporal shifts were detected for green sea turtles ( Chelonia mydas ), Guiana dolphins ( Sotalia guianensis ), Magellanic penguins ( Spheniscus magellanicus ), and brown boobies ( Sula leucogaster ). Diets generally reflected opportunistic feeding behaviour and were likely influenced by fishing discards and changing prey availability. Although temporal factors explained only a small proportion of the overall dietary variation, our findings might indicate potential food‐web restructuring and increased reliance on lower‐value prey. Such trends may signal broader ecological shifts driven by cumulative anthropogenic and climatic pressures. The dietary changes documented here highlight the urgent need for long‐term monitoring and adaptive management strategies to mitigate ecosystem degradation and biodiversity loss.