Maintaining proper freshwater and marine inputs is essential for estuarine function. Alteration of freshwater flows into small tributaries that traverse the uplandestuarine margin may be especially problematic, e.g., by impacting the nursery areas for juvenile finfish and shellfish. We used stomach contents and stable isotope analysis (δ 13 C, δ 15 N) to examine effects of freshwater flow alterations on the trophic ecology of juvenile common snook (Centropomus undecimalis) in four mangrove creeks with different freshwater flow regimes. Diet diversity in less degraded creeks was greater than in more degraded creeks, and the importance (by % mass) of the top three preys was disproportionately higher in the more degraded creeks. Stable isotope measures of trophic diversity corroborate these trends, suggesting higher intraspecific trophic diversity in less degraded creeks. The difference in diet diversity of juvenile snook may be an indicator of an overall change in ecosystem function and these shifts in food web structure may affect the rate that juveniles of this and other species with similar habitat requirements successfully join the adult population.

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