Nekton use of a Phragmites australis marsh on the Hudson River, New York, USA

Recently, Phragmites australis (common reed) in North American wetlands has changed from a species with limited distribution to an invasive species producing dense monospecific stands. This expansion has forced out other wetland vegetation, potentially changing the functions of these ecosystems. Little research has focused on whether P. australis stands serve as valuable wetland habitat and foraging areas for terrestrial animals and resident marsh nekton. This study addressed the effect of different hydrologic and geomorphic conditions among P. australis stands on abundance of resident nekton in Piermont Marsh, located on the lower Hudson River Estuary. Three P. australis-dominated sites (erosional creekbank, depositional creekbank, interior) were sampled for nekton using bottomless lift nets during day and night spring high tides during the months of July, August, and September, 1998. Hydrology data were collected for ten continuous days during each sampling period and included mean flooding depth, duration, and frequency for the three sites. Species captured on the marsh surface included Fundulus heteroclitus (common mummichog), Palaemonetes pugio (dagger-blade grass shrimp), Callinectes sapidus (blue crab), and Uca minax (brackish water fiddler crab). Results indicate that nekton and macrobenthos are using all areas sampled, and measured densities are comparable to those measured in some non-P. australis dominant wetlands elsewhere on the Hudson River. Although no strong correlation was made between nekton densities and hydrology, definite patterns were observed in the data. The results indicated that additional variables, such as geomorphology, might interact with hydrology to influence nekton use of the marsh surface. Although exact mechanisms controlling spatial variation of nekton use within P. australis stands still need to be elucidated, P. australis does seem to serve as nekton habitat.