American manatees adjust their diet composition and trophic niche breadth across different coastal regions

Marine mammals can exhibit high plasticity in foraging strategies, but how such plasticity is driven by environmental conditions is poorly understood. The American manatee ( Trichechus manatus ), a large, endangered herbivore, inhabits marine, estuarine, and freshwater environments. To better understand their resource use, we analyzed dietary differences across three large Brazilian regions—the Northern Coast (NC), Dry‐Northeastern Coast (Dry‐NEC), and Humid‐Northeastern Coast (Humid‐NEC). The δ 13 C and δ 15 N values of manatee tissues increased from the NC to the Northeastern Coast. Stable isotope mixing models revealed that manatees from the Dry‐NEC feed almost exclusively on seagrasses, while those from the NC rely predominantly on saltmarsh vegetation. In the Humid‐NEC, manatees had a notable contribution from macroalgae, and exhibited the greatest dietary and habitat use diversity among the regions. These spatial patterns advance our understanding of large‐scale habitat use, guiding the establishment of marine protected areas to safeguard manatees and their habitats.