Habitat utilization patterns determine the physiological condition of Cynoscion regalis during estuarine residency

Abstract

For many species, quantifying nursery function of estuarine habitats, including tidal salt marshes, for early life stages is complicated by multiple habitat shifts over their period of estu- arine residency. Our study relates the physiological condition of young of the year (YOY) of a mar- ine transient species (weakfish Cynoscion regalis) to the quality of habitats frequented during their period of estuarine residency by examining their physiological condition (energetic reserves in the form of triacylglycerol, normalized to the expected changes with length) as a function of habitat use patterns and corresponding stable isotope signatures. In addition, for C. regalis preparing to emi- grate offshore to wintering grounds, we evaluated the benefit of energetic reserves towards miti- gating over-winter starvation in the context of individual metabolic rate. We found significant spa- tial distribution in the physiological condition of YOY C. regalis over their period of estuarine residency, with those utilizing polyhaline salt marshes consistently having comparable or higher condition across all years of the study. For C. regalis preparing to emigrate to offshore, we found inter-annual variability both in the relative utilization of marsh versus open bay regions and in their associated energetic reserves. However, variability in reserves was not reflected in the potential benefit of reserves in mitigating over-winter starvation, suggesting plasticity in energy allocation for YOY C. regalis. These results demonstrate that both the habitats utilized over the period of estu- arine residency and larger-scale inter-annual variability can affect the condition and preparedness of YOY marine transients for the rigors of migration and over-wintering.