Ecological Thresholds for Salt Marsh Nekton and Vegetation Communities

摘要: Salt marsh vegetation and nekton respond to stressors in estuarine systems, providing ideal indicators of change. Here we characterize the structure these communities along a gradient anthropogenic stress (e.g., human population size watersheds, degree hydrological alteration marshes), identify ecological thresholds that are linked community condition, provide potential decision for land managers based on an evaluation condition. data (species composition abundance) were compiled from over 180 discrete sets marshes Atlantic coast Maine Virginia. Using multivariate techniques Principal Component Analysis, Canonical Correspondence Analysis Similarities), patterns change hydrologic impact watershed development elucidated. Several levels complexity, individual species’ abundances, relative abundances life history-based groups used metrics thresholds. The displayed shifts gradient) surrounding resident fish-dominated at watersheds with low populations shrimp-dominated (Palaemonidae species) high populations. Vegetation reference (relatively hydrologically undisturbed) dominated by obligate halophytes salt meadow grasses) proportions invasive plants. Impacted tidally restricted) had fewer halophytic wetland plants, more facultative plant species, higher species. Shifts characteristics toward impacted state can be as upon which based. For example, detection declining killifish transient fish increasing Palaemonidae shrimp (the threshold metrics), would indicate changing moderate poor condition threshold), thereby triggering management actions. Ecological presented both context desired resource goal (good, moderate, condition) evaluate responses restoration activities or overall community. Findings this study most directly relevant northeastern US marshes, but methods derive applied other regions.