a wrack line

Figure 7. A wrack line. (Photograph by the author. More about the photograph)

Moving over to the east bank of the river, we can follow River Road to the River Road Park, the site of the fishing pier you saw at the start of this tour. The photo here shows a tangled mat of Spartina debris washed ashore by a storm.

Why aren’t maintenance personnel cleaning this mess up? This stranded debris serves as a vital nutrient source in the estuary. The grasses, inedible to most organisms in the estuary, are degraded by bacteria and fungi. The bacteria and fungi serve as a primary food source for snails and crabs, which are in turned preyed upon by birds and small mammals. Each winter the Spartina dies off, and the dead husks fall into the water. If this debris were carried out to sea, along with the bacteria, the estuary would not be able to sustain itself. Luckily, winter storms wash the debris ashore, where conditions are perfect for decay. The debris also provides shelter for the crabs, mice, and alligators (warning signs in the area attest to the alligators). Finally, the remnants of the decayed plants serve to build up the soils and sediments in the estuary.

Living grasses are also colonized by bacteria when submerged. Snails such as marsh periwinkles (Littorina irrorata) scrape the bacteria off of living grasses, moving up and down the blades in time with the tides.