Ontogenetic environmental reconfiguration in Sphyrna lewini: Estuarine nursery dependence, offshore recruitment, and ecological connectivity across the marine-estuarine continuum

The scalloped hammerhead shark, Sphyrna lewini, exhibits pronounced ontogenetic changes in habitat use across the marine–estuarine continuum. Neonates and young juveniles repeatedly occupy shallow coastal and estuarine environments that function as developmental nursery habitats, whereas larger juveniles progressively expand their movements toward continental-shelf and oceanic environments. However, this transition is not strictly unidirectional, as trophic evidence indicates renewed use of coastal resources during later ontogenetic stages. Across its geographic range, nursery habitats show recurrent recruitment, seasonal use, and juvenile residency, while telemetry studies demonstrate extensive horizontal and vertical movements in larger individuals. These habitat transitions are accompanied by changes in trophic position and resource use, indicating that ontogenetic movements represent ecological reorganization rather than simple geographic displacement. Population-genetic studies further reveal geographically heterogeneous connectivity, demonstrating that extensive individual mobility can coexist with spatially structured populations. Together, these patterns indicate that S. lewini organizes its life history through repeated redistribution among complementary environmental compartments, with the functional importance of particular habitats changing across ontogeny. This case supports the Dynamic Environmental Reconfiguration Hypothesis by demonstrating that substantial environmental reconfiguration does not require freshwater dependence or extreme euryhalinity. Instead, ecological plasticity can emerge through ontogenetic redistribution of habitat, trophic resources, and movement among estuarine, coastal, shelf, and oceanic environments.