Habitat Suitability for a Unique, Fully Marine American Manatee ( Trichechus manatus ) Population Primarily Depends on Presence of Submarine Freshwater Springs

Abstract

The American manatee ( Trichechus manatus ) requires freshwater mainly from rivers and springs to maintain osmoregulatory balance in saline environments. However, in Brazil's semi‐arid Potiguar Basin, manatees now rely solely on submarine freshwater springs because hypersaline estuaries have become unsuitable sources of freshwater. We applied MaxEnt modeling to presence‐only data (sightings and filtered telemetry records) to produce habitat suitability maps and identify the environmental conditions driving habitat use. Telemetry locations were spatially and temporally thinned and subsampled to balance individual contributions, and alternative thinning scenarios were evaluated—while the model with the lowest level of spatial filtering showing the most stable performance was retained for inference. Model performance and fit were high (AUC = 0.979; CBI = 0.943, training gain = 2.76), and model suitability was strongly structured by proximity to submarine springs, with predicted probability declining sharply beyond 4–8 km. Seagrass presence contributed secondarily to suitability, whereas the other variables showed limited independent explanatory power at the regional scale. Suitable habitat was highly localized, comprising approximately 4% (301 km 2 ) of the modeled coastal area and concentrated near Icapuí (Ceará) and Areia Branca (Rio Grande do Norte). These findings reveal the strong ecological constraints shaping this fully marine manatee population and highlight the critical role of submarine freshwater springs and seagrass meadows in sustaining manatee presence in hypersaline coastal systems. Protecting these key resources is essential for conservation planning in a region facing increasing freshwater limitation and expanding offshore development.

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