Submerged aquatic vegetation surveys: A grass act

By: Jim Hawhee, APNEP
January 6, 2015

Hilde Zenil of East Carolina University conducts surveys

Imagine someone whose only pleasure is to count blades of grass… -John Rawls

Submerged aquatic vegetation. Scientists casually refer to it as SAV and you might know it as seagrass, though the stuff in North Carolina grows mostly in our embayed sounds. It’s extremely important habitat for fish and waterfowl, and by extension it’s important to the hunters and fishermen that reside in and flock to eastern North Carolina.

Like the canary in the coal mine, these aquatic grasses are an important indicator of water quality in the sounds. Specifically, they are sensitive to nutrient and sediment inputs from upstream rivers which can limit how much light they receive. Rough estimates in the 1980s suggested that up to 200,000 acres of SAV existed in North Carolina’s sounds. In 2011, an APNEP-led effort to survey SAV from the air accounted for 138,000 visible acres.

Led by Dr. Dean Carpenter, APNEP’s efforts to survey SAV habitats in concert with our partners have continued. Last year was particularly fruitful, and staff has enjoyed getting out on the water to participate in field surveys. Here are a few of the developments we saw in 2014:

• New aerial surveys: In partnership with the N.C. Department of Transportation and the N.C. Division of Marine Fisheries, APNEP has completed a second coastwide aerial survey of SAV in the Albemarle-Pamlico region using sophisticated plane-mounted cameras. For the first time, environmental managers will have the ability to detect changes in SAV in the sounds over time. Analysis of the flight imagery remains and the final maps are expected in 2015.
• Boat-based sonar surveys: APNEP is supporting an effort led by East Carolina University to survey the sounds’ shorelines using sonar. Because turbidity is higher on the western side of the sounds, boat-based sonar can find SAV in areas where it is difficult to detect by air. This work builds on a prior N.C. Coastal Recreational Fishing License Fund grant used to develop these boat-based protocols. In 2014 the circumference of Albemarle Sound was surveyed, with areas of Pamlico Sound planned for next year.
• Sentinel site preparations: APNEP took preliminary steps to establish a sentinel site network for SAV monitoring. Budget considerations have resulted in a 5-year cycle for a full SAV “census,” but APNEP staff and partners plan to visit these “sentinel sites” more frequently to detect gradual changes in SAV coverage. In addition to sonar-based methods, sentinel site surveys may include low-tech options like placing quadrats, identifying dominant species and refining estimates of cover percentages. Monitoring at these sites will also provide valuable data for aerial photo interpretation.

SAV has great ecological and economic value, and North Carolina’s SAV resources are more abundant than most. Located at the confluence of the warmer Gulf Stream and the cooler Labrador Current, the Albemarle-Pamlico Sounds are critical to fisheries in North Carolina and along the east coast.

The only estuary in the continental U.S. larger than the Albemarle-Pamlico is the Chesapeake Bay, where recent SAV estimates are less than half of that found here due to substantial water quality degradation. Florida’s Indian River Lagoon provides another cautionary tale, where a drastic 60% dieback of its seagrass resulted in a seismic ecosystem shift and impacts to the local economy estimated at $235 million to $470 million annually.

A sustained monitoring effort is critical to protecting and enhancing SAV in the Albemarle-Pamlico Sounds. We’ll look forward to reporting back on the status of this resource when the data have been analyzed.

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