Differences in juvenile trophic niche for two coastal fish species that use marine and estuarine nursery habitats

In coastal regions, age-0 juveniles of many fish species are capable of recruiting to either marine or estuarine nursery habitats, yet the ecological consequences for cohorts that use marine versus estuarine nurseries is poorly understood. In the present study, stable isotope (δ13C, δ15N) and stomach contents data were used to compare trophic ecology associated with differential habitat use for age-0 bluefish Pomatomus saltatrix and bay anchovy Anchoa mitchilli from 2 habitats: Maryland’s (USA) inner continental shelf (shelf) and lower Chesapeake Bay (estuary). Bluefish occupied equivalent trophic positions (approx. 4.0 to 4.2; δ15Nand diet-based estimates) as tertiary consumers in the shelf and estuary. In contrast, bay anchovy were secondary-tertiary consumers with trophic position estimates of 3.5 to 3.8 in the shelf and 3.5 in the estuary. A C:N ratio proxy for lipid content was higher in the shelf cohorts for both species, and weight-at-length was also higher for shelf bay anchovy than estuarine bay anchovy. Estuarine cohorts of both species occupied a larger isotopic niche (i.e. convex hull area), yet 2-source mixing model results indicated that estuarine cohorts derived >80% of their biomass from pelagic food webs alone. Conversely, shelf cohorts more equitably integrated pelagic (bluefish: 45 ± 7% [SD], bay anchovy: 46 ± 12%) and benthic food webs. The present study indicates that the juvenile trophic niche of these species can vary significantly across habitats and provides initial evidence that cohorts recruiting to Maryland’s shelf can realize more diverse (i.e. utilization of multiple food webs) or superior (i.e. increased condition — bay anchovy only) foraging conditions than cohorts recruiting to proximal estuaries.