| Excessive growth of macroalgae in estuarine systems is becoming increasingly common along coastal communities throughout the world. However, little research has been conducted on the impacts of this increasing macroalgal biomass on the ecological dynamics of nearby salt marshes. This research is designed to assess the distribution of macroalgae in Rhode Island salt marsh communities and examine the ecological changes in community structure associated with these macroalgal blooms.;While macroalgae has been observed in Rhode Island salt marshes, this study provides the first record of bloom abundance and species composition. Monthly surveys, conducted in nine fringing salt marshes throughout Rhode Island, revealed macroalgae to be present at each site during every month. However, macroalgal accumulation varied seasonally, with the highest densities occurring during the summer and fall. These blooms were dominated by fucoid species that comprised almost 75% of the total yearly abundance. While macroalgae occurred >10 m from the lower marsh edge, nearly 80% of the annual biomass was found within the first two meters of the lower marsh zone.;Spartina alterniflora, the dominant native cordgrass in the lower marsh zone, may be significantly impacted by macroalgal blooms. Through controlled mesocosm experiments, we found the release of nitrogen from the decomposing macroalgae into the underlying sediment provides S. alterniflora limiting nutrients and facilitates its growth. However, this facilitative interaction was not observed during manipulative in situ experiments. As previous fertilization experiments have consistently shown an increase in S. alterniflora growth following nitrogen addition, we believe our inconclusive field results were due to naturally occurring tidal cycles removing nutrients from the system before they could be incorporated into the sediment. There was no negative impact on S. alterniflora associated with shading or smothering from macroalgal accumulations. Additionally, we did not find evidence of higher trophic impacts associated with macroalgal accumulation.;This research provides an important baseline for understanding the impact of macroalgal blooms on salt marshes. Since increases in temperature and nutrient levels associated with global climate change are predicted to increase the number and severity of macroalgal blooms, monitoring these fragile ecosystems is important in order to sustain their enormous economic and recreational value. |
