Monitoring food web changes in tide-restored salt marshes: A carbon stable isotope approach

Primary producer (angiosperms, macroalgae, submerged aquatic vegetation), suspended participate matter, and Fundulus heteroclitus isotope values (δ13C, δ15N, δ34S) were examined to assess their use as indicators for changes in food web support functions in tidally-restored salt marshes. Study sites, located throughout the southern New England region (USA), ranged from Spartina alterniflora-dominated reference marshes, marshes under various regimes and histories of tide restoration, and a severely tide-restricted Phragmites australis marsh. Fundulus δ13C values were greater for fish from reference Spartina marshes than for fish from adjacent tide-restricted or tide-restored marshes where higher percent cover of C3 plants, lower water column salinities, and more negative dissolved inorganic δ13C values were observed. The difference in Fundulus δ13C values between a tide-restricted Phragmites marsh and an adjacent reference Spartina marsh was great compared to the difference between marshes at various stages of tide restoration and their respective reference marshes, suggesting that food web support functions are restored as the degree of tidal restriction is lessened. While a multiple isotopic approach can provide valuable information for determining specific food sources to consumers, this study demonstrates that monitoring Fundulus δ13C values alone may be useful to evaluate the trajectory of ecological change for marshes undergoing tidal restoration. © 2006 Estuarine Research Federation