REESTABLISHMENT OF MELAMPUS-BIDENTATUS (SAY) AND OTHER MACROINVERTEBRATES ON A RESTORED IMPOUNDED TIDAL MARSH - COMPARISON OF POPULATIONS ABOVE AND BELOW THE IMPOUNDMENT DIKE

Macroinvertebrates were studied on an impounded marsh in Stonington, Connecticut, that has converted from a Typha-dominated system to one with typical tidal marsh vegetation during the 12 yr following the re-introduction of tidal flushing. Regions of marsh above and below the impoundment dike were compared in order to assess the extent to which tidal marsh invertebrates have recolonized the restored region. Marshes below the impoundment dike consist of two types: marshes that are dominated by Spartina patens (Ait) Muhl and have remained relatively stable for several decades and marshes in which large areas have changed form nearly pure stands of S. patens to stunted Spartina alterniflora Loisel. and forbs during the last 40 yr coincident with an increase in sea level relative to the marsh surface. In most of the areas occupied by S. alterniflora, varying amounts of S. patens persist. Melampus bidentatus Say and other tidal marsh invertebrates have become established on the restored impounded marsh and occur at moderate densities on the stable bayfront marshes and in some areas of the bayfront marshes that have exhibited dramatic vegetational change. The mean density of Melampus on the restored marsh was 83 . 0.25 m-2, that on the S. patens-dominated bayfront marshes was 98 . 0.25 m-2 and that on the changing bayfront marshes was 117 . 0.25 m-2. Within each marsh region, snail density varied in relation to plant cover and elevation. The size structure of the Melampus populations in different marsh regions differed. On the restored marsh 83% of the snails exceeded 8 mm in shell length, while on the S. patens-dominated marshes 95% of the snails were less-than-or-equal-to 8 mm. Because of these differences in snail size, the mean shell-free biomass of Melampus was 2 x greater on the restored marsh (1.24 g dry wt . 0.25 m-2) than on the S. patens-dominated marshes (0.63 g dry wt.0.25 m-2). The mean biomass of Melampus on the changing bayfront marshes was 1.01 g dry wt . 0.25 m-2.