NOAA EPP Summer Interns 2004
Napoleon Paxton :: "Determining the Maximum Depth of Seagrass Beds along the Southern Outer Banks with an Optical Model"

Napoleon with test equipment underwayNapoleon Paxton assisted NOAA Beaufort Laboratory scientists in determining the maximum depth of seagrass beds along the Southern Outer Banks. During his summer internship he was mentored by Dr. J. Kenworthy (vitae) and Dr. Patrick Biber (vitae). The goal of this project was to develop a long-term record of seagrass bed extent, focusing primarily on the historical changes that have occurred to the deep-edge, and tie this in with historical changes in water-quality.

Introduction to Research

What are Seagrasses
Seagrasses are vascular plants that grow completely underwater. They are a part of a larger group of underwater plants called SAV (Submerged Aquatic Vegetation). SAV have special adaptations to help them survive in the aquatic environment. The leaves and stems lack the waxy cuticle that is characteristic of most terrestrial plants to allow for easy exchange of gasses and nutrients between the plant and surrounding water. Specialized air-filled cells, called aerenchyma, are present in the leaves and stems and provide the plant with additional buoyancy and support. Seagrasses are distinguished from other SAV because seagrasses require a certain amount of salinity to survive.

Importance of Seagrass
There are many important ecological roles of seagrass in the aquatic environment. They provide food and habitat for waterfowl, fish, shellfish, and invertebrates. The seagrasses serve as nursery habitat for many species of fish, such as young spot and striped bass, which seek refuge from predators in the grass beds, blue crabs also hide in seagrass. Seagrasses provide oxygen in the water column as part of the photosynthetic process. Seagrasses filter and trap sediments that can cloud the water and bury bottom-dwelling organisms, such as oysters. They protect shorelines from erosion by slowing down wave action, and they remove excess nutrients such as nitrogen and phosphorous, that could fuel unwanted growth of algae in surrounding waters. These nutrients are also required for seagrass growth and reproduction, but in much lower water-column concentrations.

Common types of Seagrass
The two types of seagrasses along the Southern Outer Banks are eelgrass (Zostera marina), and shoalgrass (Halodule wrightii). Eelgrass is the most common seagrass in this area and it is more prevalent in temperate climates. Hot weather puts stress on this species of seagrass. Shoalgrass is a more tropical seagrass and is more prevalent during the summer months on the Outer Banks. Both of these species of seagrass are normally found in the same grass beds.

This paper can be found in it's entirety at: