Cordgrass, Spartina alterniflora, is the most visible plant in Georgia salt marsh estuaries. Scientists initially thought that decaying Spartina detritus was the most important source of plant matter for both marsh and estuarine food webs. But further research carried out at the University of Georgia Marine Institute on Sapelo Island revealed that microscopic algae growing in the water, on mudflats, and in beach sands were equally important in nourishing the exuberant life along the coast.
Diatoms, golden-brown algae encased in hard silica shells termed frustules, grow both in estuarine water and in marsh muds. On the mudflat in the photo, swarms of mud snails plow up the surface sediment, slurping up algae and small invertebrates. The netting 'corral' placed on the mudflat kept out the snails, allowing a brown lawn of benthic diatoms to move up to the surface to grow in the sun during low tide.
In late summer and early fall, a different microscope alga, a green-pigmented euglena, can form bright green blooms on the lower beach. The photo below shows a bloom of euglenae on Nannygoat Beach on Sapelo Island in September 1983. When the sun is too bright, the flagellated algal cells move down into the cooler subsurface sand, but if the beach is shaded with an umbrella or towel, the algae will form a green patch on the surface again.