Responses of salt marsh ecosystems to mosquito control management practices along the Atlantic Coast (U.S.A.)

Open marsh water management (OMWM) of salt marshes modifies grid-ditched marshes by creating permanent ponds and radial ditches in the high marsh that reduce mosquito production and enhance fish predation on mosquitoes. It is preferable to using pesticides to control salt marsh mosquito production and is commonly presented as a restoration or habitat enhancement tool for grid-ditched salt marshes. Monitoring of nekton, vegetation, groundwater level, soil salinity, and bird communities before and after OMWM at 11 (six treatment and five reference sites) Atlantic Coast (U.S.A.) salt marshes revealed high variability within and among differing OMWM techniques (ditch-plugging, reengineering of sill ditches, and the creation of ponds and radial ditches). At three marshes, the dominant nekton shifted from fish (primarily Fundulidae species) to shrimp (Palaemonidae species) after manipulations and shrimp density increased at other treatment sites. Vegetation changed at only two sites, one with construction equipment impacts (not desired) and one with a decrease in woody vegetation along existing ditches (desired). One marsh had lower groundwater level and soil salinity, and bird use, although variable, was often unrelated to OMWM manipulations. The potential effects of OMWM manipulations on non-target salt marsh resources need to be carefully considered by resource planners when managing marshes for mosquito control.