Relative effects of Littoraria irrorata and Prokelisia marginata on Spartina alterniflora
Spartina alterniflora salt marshes along the southeastern United States are some of the most productive and well studied ecosystems in the world. The role of physicochemical forces in regulating Spartina growth is well understood, while the importance of grazers remains less clear. Recent studies have shown that the abundant marsh periwinkle, Littoraria irrorata, can exert strong control over Spartina through its grazing activities, but relatively little is known about its relative effects in comparison to other marsh plant consumers. To test the relative importance of snail and insect consumers on Spartina biomass, we conducted a 7-mo field experiment testing top-down regulation of Spartina with all combinations of L. irrorata (removed, control, c. 215 periwinkles m-2) and Spartina planthopper, Prokelisia marginata (removed, control). Snail removal resulted in a 50% increase in Spartina biomass while removal of planthoppers had no detectable effect. Planthopper density also increased by 50% when snails were excluded. In this South Carolina marsh, L. irrorata exerts a stronger top-down control of Spartina than P. marginata. These results indicate trophic cascade regulation of Spartina salt marsh is more likely to occur through the predator(s)-Littoraria-plant interaction than through the predator(s)-Prokelisia-plant relationship. © 2006 Estuarine Research Federation.
Gustafson, DJ; Kilheffer, J; Silliman, BR
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