Nekton utilization of tidally restricted, restoring, and reference New England salt marshes

Salt marshes provide important habitat for estuarine nekton (fishes and decapod crustaceans), yet tidal flow to New England marshes is often restricted due to roads, causeways, and culverts. The objectives of this study were to determine the most effective method for sampling salt marsh nekton and use this method to quantify nekton use of tidally restricted, restoring, and reference New England salt marshes. Throw traps are often used for sampling nekton in specific salt marsh microhabitats. When compared to seines, another common sampling gear, throw traps were more efficient, quantitative, and easier to use. Throw traps were used to sample multiple habitats within a tidally restricted and unrestricted salt marsh at Hatches Harbor, Provincetown, MA over a one-year period. Nekton use of tidal creeks and the salt marsh surface was similar in both marshes, but utilization of pools differed substantially on either side of the tide-restricting dike. In the same Cape Cod marsh, restricted salt marsh pools provided overwintering habitat for the mummichog, Fundulus heteroclitus. Unrestricted pools were not utilized by this species during the winter. Nekton responded rapidly to restoration of the tidally restricted Galilee salt marsh in Narragansett, RI. After two years of tidal restoration, densities of F. heteroclitus, Fundulus majalis , and Callinectes sapidus were higher than under restricted conditions. Species richness and densities of Lucania parva and Cyprinodon variegatus decreased after restoration. Changes were continuing after two years and studies of longer duration are needed to assess the long-term responses by nekton to restoration. In a meta-analysis, nekton use was related to the degree of tidal restriction at three sites. Nekton density and richness were similar between the restricted and unrestricted sides of the two moderately restricted marshes, but both were lower on the restricted side of the severely restricted marsh. Density and richness each increased by approximately 150% with restoration of the severely restricted marsh; smaller changes were observed with restoration of the other two marshes. These patterns suggest that severe tidal restrictions result in degraded nekton communities and the most dramatic shifts towards more natural assemblages will occur with restoration of severely restricted salt marshes