Implications for Impoundment
Management and Restoration

      
Recent research at Merritt Island National Wildlife Refuge (MINWR), Florida has found that saltmarsh impoundments reconnected by culverts to the Indian River Lagoon provide habitat to estuarine sport fishes, and also export substantial quantities of fish biomass to adjacent estuarine waters.  Closing water control structures and managing water levels appears to benefit avian wildlife by increasing prey abundance and access to prey, but at the expense of saltmarsh forage-fish export and nursery functions to estuarine predators.  Where mosquito control and wildlife management are not a priority, resource managers at MINWR are increasing saltmarsh access to estuarine fishes by restoring selected impoundments (opening water control structures or completely removing dikes). Comparison among habitats in an open impoundment that would be affected by restoration efforts (i.e. estuary shoreline, perimeter ditches, and shallow creeks) showed that fish use varied among habitats.  Fish abundance and community structure along the estuary shoreline (although fringed with marsh vegetation) were not analogous to marsh creeks and ditches.  Perimeter ditches provided deep-water habitat for large estuarine predators, and shallow creeks served as an alternative habitat for resident fishes when the marsh surface was dry. Regardless of restoration strategy (complete removal of dikes or opening of a sufficient number of culverts), forage-fish export from seasonally flooded marshes at MINWR would be restored.  Restoration of nursery function is probably dependent upon marsh morphology (amount of creeks and embayments reconnected to the estuary relative to loss of perimeter ditch), and marsh location with respect to estuarine spawning sites and larval dispersal patterns.