Submerged aquatic vegetation, topography and flow characteristics in the upper, tidal Hudson River: Progress toward a predictive habitat model

Submerged aquatic vegetation (SAV) plays a critical role in biogeochemical cycling, primary productivity, sediment dynamics and current flow within the systems they inhabit. SAV communities in the Upper Hudson River Estuary are comprised of species assemblages dominated by two very morphologically distinct species: the native Vallisneria americana, which has wide-strap shaped leaves that are completely submerged underwater, and the invasive Trapa natans, which produces leaf rosettes that float at the water's surface. Using characteristics of modeled tidal/riverine flow, we examined the distribution and composition of the predominant SAV in the estuary. SAV habitat space was, on average, well described by depth and flow. From a hydrodynamic standpoint however, the two species occupied very similar niche spaces. Species-specific distribution patterns and co-occurrence rates did not appear to be strongly controlled by physical tolerances of topography or flow. Other ecological drivers such as disturbance regimes, dispersal strategies, plant-animal interactions, and sediment chemistry and composition might explain distribution patterns and T. natans expansion more accurately, rather than hydrodynamics alone. Sixty years after reaching the Hudson River Estuary, T. natans appears unable to fully displace V. americana, despite significant overlap in habitat space and spatial distribution. Future management of the exotic T. natans should consider its role as an ecosystem engineer, adding to overall habitat diversity, rather than the current focus on its perceived invasibilty.