STABLE ISOTOPE ANALYSIS OF FUNDULUS HETEROCLITUS AND THE EFFECTIVENESS OF DITCH-PLUG RESTORATION AT THE SPRAGUE RIVER SALT MARSH, PHIPPSBURG, MAINE

The Sprague River Salt Marsh is a back-barrier salt marsh adjacent to Seawall Beach in Phippsburg, Maine. The Sprague River Salt Marsh has undergone significant modification by humans over the past 300 years with evidence of three different episodes of ditching documented. In an effort to restore sections of the marsh by creating pool habitats, the U.S. Wildlife and Fisheries Service plugged several of the ditches in the southern end of the marsh between 2002 and 2006. The purpose of this study is to evaluate the efficacy of the restoration method by studying differences in food web dynamics and water quality in ditch plugs versus natural pools. Stable carbon and nitrogen isotopes from muscle tissue and liver from Fundulus heteroclitus, vegetation from biomass cores, sediment from surface cores, and salt marsh vegetation were examined in one ditch-plugged pool, two pools that had been natural but were enlarged in order to obtain salt marsh peat to plug preexisting ditches, and three natural pools. Water quality parameters including pH, temperature, dissolved oxygen, and specific conductivity were measured in 215 pools throughout the marsh to identify pools for more detailed analysis. Our results show that livers are consistently depleted in ¹³C relative to muscle tissue likely reflecting the presence of more lipids in liver relative to muscle. Additionally, the C and N isotopic composition of F. heteroclitus tissues indicate that significant differences exist between fish sampled from several of ditch-plugged pools verses fish collected from the natural pools, likely reflecting differences in the source of dominant primary production. Additional analyses are currently underway to evaluate our preliminary interpretations.