Abstract
Resilience is currently a key theme within salt marsh ecological studies. Understanding the factors that affect salt marsh accretion and elevation gains is of paramount importance if management of these ecosystems is to be successful under increasing synergistic stresses of storm surge, inundation period, and eutrophication. We present the results of salt marsh fucoid algae (ecads) removal experiments on Spartina alterniflora abundance, production and decomposition, and the sedimentary dynamics of two marshes on Cape Cod, Massachusetts. The presence of the thick layer of marsh fucoids had a significant and positive influence on sediment deposition, accretion, and concentration of water column particulates, while it inhibited water flow. Decomposition rates of S. alterniflora in the field were significantly higher under the fucoid macroalgae layer, and, in lab experiments, S. alterniflora seedlings added more leaves when the marsh fucoids were present. In contrast, fucoids caused a significant decrease in S. alterniflora seedlings’ survival in the field. We found that marsh fucoids are stable despite not being attached to any substrate, and field surveys revealed a relatively widespread, but not ubiquitous, distribution along outer Cape Cod. Salt marsh fucoid algae directly and substantially contribute to salt marsh sediment elevation gain, yet their potential inhibitory effects on colonizing S. alterniflora may counteract some of their overall contributions to salt marsh persistence and resilience.
Highlights
Climate change-driven sea level rise and the increased intensity and frequency of major coastal storms have brought increased attention to the protective function of vegetated ecosystems and their substantial economic and ecological benefits (e.g., Costanza et al 2008; Borsje et al 2011; Spalding et al 2013)
There was no obvious pattern related to the presence or absence of marsh fucoids; they occur on both bay and ocean sides, in riverine and back-barrier marshes, and in locations that have strong anthropogenic influences nearby as well as marshes that are relatively isolated from extensive watershed upland development (e.g. Pamet Harbor at Corn Hill)
In the marsh fucoid movement tracking, we found that in every case except one, the flagging was re-located within 3 meters of its original location, which corresponds to the accuracy limit of the handheld GPS
Summary
Climate change-driven sea level rise and the increased intensity and frequency of major coastal storms have brought increased attention to the protective function of vegetated ecosystems and their substantial economic and ecological benefits (e.g., Costanza et al 2008; Borsje et al 2011; Spalding et al 2013). Initial colonization of a salt marsh by fucoids occurs via algal fragments (Mathieson et al 2006) and vegetative growth results in the algae becoming entangled among the vascular plants and often partially buried in the sediments. Based on their high biomass, and concentration in the lowest portions of the marsh (Tyrrell et al 2012), we hypothesized that they may have important roles in sediment accumulation and stabilization at the most dynamic portion of the marsh. We suspected that this potential to enhance sediment deposition and elevation gain may decline with increasing distance from the lowest portion of marshes
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