Carolina Environmental Diversity Explorations

Cape Fear estuaries · By Steve Keith

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.

Definitions

nutrient n.
A substance that provides nourishment essential for growth and the maintenance of life.
estuary n.
The mouth of a river where it meets the sea, and where freshwater from the river mixes with the salty water of the sea. [more]
sediment n.
Solid fragments of inorganic or organic material that come from the weathering of rock and are carried and deposited by wind, water, or ice. Sediments may also be formed from chemical, biochemical, or biological materials. [more]