The Albemarle-Pamlico's Underwater Meadows

Hidden underneath the estuary's surface lies a little-known, but vital habitat

Kelsey A Ellis

May 17, 2021

Slender green leaves stretch from the estuary's sandy bottom almost to the water's surface. Small fish, shrimp, and crabs swim among the grasses as they sway in the gentle current. This underwater meadow, one of many in the Albemarle-Pamlico estuary, stretches for acres under the surface of the sound. Underwater grasses or submerged aquatic vegetation (SAV), known as seagrasses in saltier estuarine and marine waters, are often seen as a nuisance by boaters and swimmers - if people are aware of their existence at all. But these underwater meadows play a vital role in maintaining the diversity, health, and sustainability of North Carolina's sounds. Mapping and monitoring efforts led by the Albemarle-Pamlico National Estuary Partnership (APNEP), NC Division of Marine Fisheries, NOAA Beaufort Lab, and other partner organizations have begun to reveal the importance of this 'hidden' habitat, and to demonstrate that North Carolina's underwater meadows need our protection in order to thrive for decades to come.

*Seagrass beds such as this one can be found on the sound side of North Carolina's barrier islands.*

Why Underwater Grasses Matter

*The Albemarle-Pamlico watershed. All the streams, creeks, and rivers in the area shown ultimately flow into the Albemarle-Pamlico Estuary.*

With over 3,000 miles of open water, North Carolina's interconnected sounds constitute the second-largest estuary in the United States. The estuary is also incredibly productive, containing half of the fish nursery habitat area from Maine to Florida , and generates billions of fishing, outdoor recreation, and tourism dollars for local economies. We can thank our abundant underwater grasses for sustaining this ecosystem: seagrasses are one of the most valuable ecosystems on the planet, estimated to be worth more than $46,000 per acre due to the ecosystem services they provide.

One reason underwater grasses are so valuable is their ability to, like plants on land, improve water quality by absorbing nutrients and trapping sediment. In addition, fish, crabs, rays, and many other smaller creatures make their homes in seagrass meadows; a single acre of grasses can support as many as 40,000 fish and 50 million small invertebrates . Shorebirds and waterfowl utilize seagrasses as a source of food. "It's one of the reasons that the waters of eastern North Carolina are one of the best waterfowl viewing and hunting areas in the country," says Dr. Jud Kenworthy, retired NOAA Scientist, SAV Ecologist, and Lead of the APNEP SAV Team .

*Grass shrimp, juvenile blue crabs, and a variety of waterfowl utilize underwater meadows.*

Additionally, underwater grasses directly benefit human communities by decreasing coastal erosion and storm damage. Seagrasses' long stems and leaves help to slow down and dissipate incoming waves, while their roots hold onto mud and sand that might otherwise be swept away by strong currents. "We often think of the dunes on the barrier islands, and forget that SAV on the back barrier shelf plays a critical role in island stabilization," says Dr. Kenworthy.

Underwater grasses have supported life in our estuary for centuries, but they can't be taken for granted. Seagrasses are one of the most threatened ecosystems on earth , in decline at rates similar to tropical rainforests and coral reefs. They need ample sunlight to grow, so water that is murky with mud or microscopic algae can impede their growth. Seagrasses are also harmed by pollutants in the water. In fact, they are so sensitive to overall water quality that many states use the presence of thriving underwater meadows as an indicator that the overall water quality is relatively good. Beyond the many benefits underwater grasses provide us directly, this ability to give us insight into the health of our estuary makes it all the more vital that we understand how much submerged aquatic vegetation is present in the Albemarle-Pamlico estuary and how it is changing over time in response to human impacts.

Mapping North Carolina's Underwater Grasses

Future Mapping Efforts

Continuing to monitor how the Albemarle-Pamlico estuary's underwater meadows are changing over time is important because these two seagrass maps can't provide enough information to be sure if the decline we’ve observed between 2006 and 2013 is part of a longer-term trend. APNEP and our partners completed another set of aerial surveys in 2019 and 2020 that will result in a third submerged aquatic vegetation map, but increased boat-based monitoring is also needed in order to gather data about other factors, such as species composition, biomass, nutrient content, and estuarine water quality data, that may help to explain why seagrass extent and density are changing over time.

*One component of boat-based ground truthing of aerial imagery is using square quadrats to confirm the density of seagrass meadows.*

*Seagrass samples are also gathered from quadrats, allowing researchers to understand what species of grasses are present in our underwater meadows.*

Protecting Underwater Meadows

Continued mapping and monitoring will help APNEP and our partners to effectively protect North Carolina’s underwater meadows. Globally, it is estimated that 29% of seagrass habitat has been lost in the last century – a number that highlights the fragility of this vital resource.

Major threats to underwater grasses include water pollution, such as excessive nutrients and sediment, that decreases water quality by increasing muddiness or murkiness. Population growth near the waterways that flow into our sounds also represents a source of increased pollution for seagrass beds. Human activities that physically rip up or disturb these meadows, such as boat propellers and anchor damage, channel dredging, or bottom-disturbing fishing practices also harm seagrass growth. In the long term, sea level rise, increasing water temperatures, and decreasing barrier island stability are important but relatively poorly-understood threats to underwater grass habitat in North Carolina.

As population growth continues in the watersheds flowing into the sounds, how will North Carolina's seagrass meadows fare? In other estuaries such as the Chesapeake Bay, once seagrass beds rapidly declined, millions of dollars spent on restoration and water quality improvements have yet to result in a full recovery of this habitat. Once a seagrass bed dies, its roots can no longer hold onto mud and sediment and so the muddiness, or turbidity, of the water increases. This decreases the light available for grasses to grow, making it harder for them to recover in the future.

This means that our best bet is to make sure that we take good care of the seagrass meadows that we have. No matter where you live in the Albemarle-Pamlico watershed, you can take action to help ensure these underwater grasses provide critical habitat for fish and wildlife, improve water quality, and preserve our barrier islands for decades to come.

What Can You Do?

Use fertilizers and pesticides responsibly .
Avoid littering and dumping hazardous chemicals outside.
Drive slowly and carefully when boating in the shallow areas where seagrass grows.
Support local land conservation efforts that help to provide natural filters for excess nutrients and sediment, and aquatic pollution reduction programs such as North Carolina's Clean Marina initiative .
Volunteer for local environmental organizations .