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Q.2-07: Assessing the Consequence of Invasive Phragmites australis on Dabbling Duck Carrying Capacity

Presented by Chris Williams - Email: ckwillia@udel.edu

Phragmites australis, a non-native perennial grass, is considered a nuisance species and a form of biological pollution. Phragmites thrives in areas with reduced soil salinities and increased nitrogen availability, which is caused when woody vegetation bordering salt marshes is removed often connected with anthropogenic shoreline development. The expansion of non-native Phragmites australis into tidal wetlands of North America detrimentally affects native wildlife by altering resource utilization, modifying trophic structures, and changing disturbance regimes. Thus, it also has the potential to drastically impact dabbling duck energetic carrying capacity in salt marsh ecosystems. This research determined the impact of invasive Phragmites on dabbling duck (mallard, American black duck, green-winged teal, northern shoveler, northern pintail) preferred food (invertebrate and seed) availability by comparing energy values in non-Phragmites invaded saltmarshes (mudflat, low marsh, high marsh, and impoundments) to energy values in Phragmites dominated areas, from two locations within Forsythe National Wildlife Refuge, New Jersey, 201516. To estimate habitat specific energy supply, we collected sediment core samples, fixed with formalin, washed, dried, sorted and weighed for seeds/invertebrates. We multiplied biomass (g) by True Metabolizable Energy (TME) values to estimate species-specific dabbling duck preferred food energy availability. We further estimated habitat specific energetic carrying capacity by predicted duck-use days based on known species-specific energetic demand. For all dabbling duck species, Phragmites invaded salt marsh contain an increased amount of consumable seed energy yet reduced amount of consumable invertebrate food energy to non-Phragmites invaded habitat types. Thus, combining food types, Phragmites had equal or greater energy food than non-Phragmites habitat types and greatly increased the duck use days. However, we caution that while sufficient food energy may exist in a Phragmites invaded area, it is likely that Phragmites grass is too dense for dabbling ducks to efficiently forage and extract the energy source thus potentially lowering landscape level availability. However increased seed availability in soil strata may aid in restoration efforts.
Session: Poster Session 2 (Wednesday, August 28, 19:00 to 21:00)