HYDROPERIOD AND ITS INFLUENCE ON NEKTON USE OF THE SALT-MARSH - A PULSING ECOSYSTEM

The salt marsh surface is not a homogeneous environment. Rather, it co ntains a mix of different micro-habitats, which vary in elevation, mic rotopography, and location within the estuarine system. These attribut es act in concert with astronomical tides and meteorological and clima tological events and result in pulses of tidal flooding. Marsh hydrope riod, the pattern of flooding events, not only controls nekton access to marsh surface habitats directly but may also mediate habitat exploi tation through its influence on other factors, such as prey abundance or vegetation stem density. The relative importance of factors affecti ng marsh hydroperiod differ between the southeast Atlantic and norther n Gulf of Mexico coasts. Astronomical tidal forcing is the primary det erminant of hydroperiod in Atlantic Coast marshes, whereas predictable tides are often overridden by meteorological events in Gulf Coast mar shes. In addition, other factors influencing coastal water levels have a proportionately greater effect on the Gulf Coast. The relatively un predictable timing of marsh flooding along the Gulf Coast does not see m to limit habitat utilization. Some of the highest densities of nekto n reported from salt marshes are from Gulf Coast marshes that are unde rgoing gradual submergence and fragmentation caused by an accelerated rise in relative sea level. Additional studies of habitat utilization are needed, especially on the Pacific and Atlantic coasts. Investigati ons should include regional comparisons of similar microhabitats using identical quantitative sampling methods. Controlled field experiments are also needed to elucidate the mechanisms that affect the habitat f unction of salt marshes.