Contrasting Trophic Niche and Resource Use Dynamics Across Multiple American Horseshoe Crab (Limulus polyphemus) Populations and Age Groups

Abstract Horseshoe crabs ( Limulus polyphemus ) exhibit ontogenetic and geographic variability in migratory patterns, yet the implications of movement on their resource use dynamics remain poorly understood. Here, we evaluate horseshoe crab across ontogeny (instars 14–18 adults), sex, seasons, between two spatially distinct populations that different patterns. Multi-tissue stable isotope analyses carbon, nitrogen, sulfur were used to examine (1) sex-specific reliance pools; (2) variation isotopic niche breadth within among populations; (3) seasonal juvenile life stages. We found evidence for subtle shifts use, with increased contributions phytoplankton ontogeny, but all age groups predominantly relied sedimentary organic matter (SOM) pools. Sex-specific differences observed SOM serving as predominant source assimilated males, while females exhibited a higher dependence pools, indicating foraging or spatial preferences may be sexes. Low trophic overlap adult was evident, likely arising from patterns size constraints. Within juveniles, no observed, dietary static temporal scales, consistent limited dispersal stage. Spatial were, however, reflecting strategies populations. Our results are previous generalists provide novel insights into linkages