Lycosid Density and Species Composition along a Riparian Cobble Gradient on the Susquehanna River

Elaine Langone Center, Terrace Room

Wolf spiders are ecologically important predators, reaching high densities in most temperate ecosystems and occupying the nexus of detrital, terrestrial, and aquatic food chains. Because these spiders can engage in multiple forms of cannibalism and intraguild predation, they have a strong potential to biomagnify mercury and other heavy metals disproportionate to their size. We measured stratification of wolf spiders by mass and species along a cobble gradient at a single site along the Susquehanna River (Isle of Que in Selinsgrove, PA). One m2 quadrats were exhaustively sampled for wolf spiders between zero and nineteen meters from the river over a ten week period (N = 23). Total number of spiders and species were identified at each distance. Preliminary analysis showed total wolf spider densities peak at 5 meters from the river edge (20 wolf spiders/m2) with more modest densities of 10 spiders/m2 closer or further from the river. We found a negative relationship between relative abundance of small and large lycosids, suggesting predator avoidance. Stable isotopes will be used to estimate trophic position and the intensity of cannibalism and intraguild predation among these spiders. We will also quantify total and methyl mercury for four of the most abundant species and compare mercury levels to that of terrestrial arthropod herbivores (tetrigid grasshoppers) and aquatic invertebrates (caddisflies and mayflies). Our data should contribute to our understanding of methyl mercury transport along the aquatic-terrestrial interface of the Susquehanna River.