PARENT SESSION
Poster Session # 17: Aquatic Systems.
Thursday, August 7 Presentation from 5:00 PM to 6:30 PM. SITCC Exhibit Hall B.
Impact of fertilization on the abundance of two detritivorous snails.
McFarlin, Caroline*,1, Buck, Tracy2, Newell, Steven2, Pennings, Steven3, 1 The University of Georgia, Athens, GA2 The University of Georgia Marine Institute, Sapelo Island, GA3 The University of Houston, Houston, TX
ABSTRACT- Because of anthropogenic alterations to the global nitrogen cycle, there is increasing interest in how nutrient supply affects community structure and processes. Most fertilization studies have focused on changes in plant biomass or community composition, and only a few studies have examined how nutrient effects propagate through the food web. Salt marshes are particularly vulnerable to eutrophication because they receive nutrient inputs from adjacent watersheds. Here we examine the impact of fertilization on two detritivorous snails that feed on litter from two abundant salt marsh plants, Spartina alterniflora and Juncus roemerianus, at 19 sites within the Georgia Coastal Ecosystems LTER study area. In control and fertilized plots, densities of both snail species were positively correlated with nitrogen content of live Juncus, but were not correlated with nitrogen content of live Spartina, nitrogen content of litter from either plant species, or plant biomass (live or litter). The two snail species were negatively correlated with each other in each treatment, supporting previous studies suggesting that they compete. Fertilization significantly increased nitrogen content of live plants of both species, but did not affect the nitrogen content of either litter type, perhaps because plants resorbed nutrients from senescing leaves or because litter was in variable states of decay. Fertilization increased the biomass of Spartina litter and decreased the biomass of Juncus litter, but did not alter densities of either snail species, nor did it alter the negative correlation between species. Sites differed strongly in snail numbers, irrespective of experimental treatments. Our results suggest that impacts of eutrophication may not propagate through the food web to affect detritivore densities, possibly because eutrophication may not strongly affect litter quality, or because other factors such as competition and predation may more strongly mediate detritivore densities.
Key words: detritivores, competition, eutrophication, salt marsh