Alginate addition influences smooth cordgrass (spartina alterniflora) growth and macroinvertebrate densities

In nitrogen-limited temperate marshes, increasing nitrogen availability via biological mechanisms such as N2 fixation and organic matter mineralization may lead to elevated marsh plant growth and macroinvertebrate densities. A polysaccharide, alginate, known to enhance microbial activity was added to sediment in a salt marsh (GA, USA) and the responses of the smooth cordgrass, Spartina alterniflora, and densities of common macroinvertebrates with important roles in nutrient cycling and energy flow through detrital systems were examined. Plant characteristics and macroinvertebrate densities were measured over portions of two growing seasons between July 2007 and July 2008. Spartina alterniflora stem densities increased in the alginate treatment compared to controls after six weeks of exposure, and this difference was evident throughout the second growing season. Differences in plant heights emerged during the second growing season. Positive effects on Geukensia demissa densities occurred during both growing seasons, Littoraria irrorata densities were elevated relative to controls only in the second growing season, and no differences were observed for Uca pugnax. This potential for increased marsh productivity following carbon amendments may be useful in developing plans for salt marsh recovery.