Sippewissett Microbial Mat

The Sippewissett Salt Marsh is located along the lower eastern Buzzards Bay shoreline of Cape Cod, about 5 miles north of Woods Hole and 1 mile southwest of West Falmouth, Massachusetts, in the United States. The marsh has two regions, the Great Sippewisset Marsh to the north and Little Sippewisset Marsh to the south, separated from each other by a narrow tongue of land (Saconesset Hills). The marsh extends into an estuary in which the intertidal zone provides a dynamic environment that supports a diverse ecology, including threatened and endangered species such as the roseate tern (Sterna dougallii). The ecology of the salt marsh is based in and supported by the microbial mats which cover the ground of the marsh.

The Sippewissett Salt Marsh houses a diverse, laminated intertidal microbial mat around 1 cm thick. The mat is characterized by regular influx of sea water, high amounts of sulfide and iron, and the production of methane. The mat contains four or five distinctly colored layers. The color of each layer can be attributed to the microbial community composition and the biogeochemical processes they perform at each of the layers. The mats are often coated by green macro- and microalgae that adhere to the surface. The top, green-brown layer is composed of cyanobacteria and diatom species. A blue-green intermediate layer is formed by Oscillatoria species. Purple sulfur bacteria are found in the pink central layer. Below the pink layer, an orange-black layer is formed predominately by a single species of purple sulfur bacteria, Thiocapsa pfennigii, and spirochetes. The thin, bottom layer is made up of green sulfur bacteria belonging to the Prosthecochloris genus, though this layer is not always present. Below the mat is iron sulfide-rich sediments and remnants of decaying mats.

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