Historical food web changes in Lake Michigan inferred from isotopic analysis of archived yellow perch scales

Disturbance in aquatic ecosystems can manifest from natural or anthropogenic changes in ambient chemical-physical conditions and species introductions which can lead to top-down or bottom-up impacts on food webs.  We investigated the long-term trophic dynamics of Lake Michigan inferred from stable carbon and nitrogen isotope analysis of archived (1972-2005) yellow perch (Perca flavescens) scales.  Identifying past changes in the structure and function of the Great Lakes ecosystem is critical for adaptive management of this important resource.  δ¹³C ranged over 4 per mil, with highest values observed following 1996 and coincident with several years of near record low water levels.  Marked changes in δ¹⁵N were observed over the 33 year period, with a general decline in trophic level following 1972 and a second more subtle decline from 2003 through 2005.  These data suggest the trophic dynamics of Lake Michigan have not been static in recent decades, that numerous disturbances are super-imposed on these changes, and analysis of additional year classes of yellow perch and other sentinel species may help resolve the mechanisms leading to variability.  Additionally, this study illustrates the utility of scale archives for better understanding anthropogenic and naturally-driven variability in the structure and function of large lake ecosystems.