Using Clams to Enhance Seagrass Restoration
In early 2010, researchers at the North Carolina National Estuarine Research Reserve (NCNERR) partnered with Dr. Joel Fodrie’s laboratory at the UNC-CH Institute of Marine Sciences to investigate possible beneficial effects of hard clams (Mercenaria mercenaria) on seagrass. Seagrass beds are one of the most valuable estuarine habitats in North Carolina. They provide an excellent nursery area for many juvenile fish species. Bay scallops, blue crabs and shrimp also rely on seagrass beds.
Seagrass beds are declining in NC for a variety of reasons including degraded water quality and physical disturbance. People can damage seagrass beds by walking through them. Propellers can also cause significant damage when people drive their boats across seagrass beds. This kind of damage, called prop scars, can take a long time to recover.
Seagrass regeneration can be slow because nutrients flush through the estuary with every tidal cycle. This is where the clams may be beneficial. Clams are filter feeders, so they actively take in everything in the water column, including nutrients. As they process the water, clams produce fecal waste. This waste, called pseudofeces, remains in the sediments and may serve as natural fertilizer in seagrass beds.
To test this idea, Dr. Fodrie and his research team are placing clams in eelgrass beds in Middle Marsh, located within the Rachel Carson component of the NCNERR. First, areas of the marsh were found that did or did not have visible prop scars. One meter square plots were set up in scarred or unscarred eelgrass. Each plot received either no clams, small clams (10-20 mm shell) or large clams (30-40 mm shell). Over the spring and summer the clams will be allowed to grow. This winter, at the end of the experiment, the seagrass in all the plots will be measured to compare growth.
The results of this study will be useful in providing information to resource managers interested in seagrass restoration efforts. If clams are found to effectively trap nutrients, thereby contributing to increased seagrass growth, then clams can be placed in areas where seagrass has been damaged. This is a natural and relatively cheap way to help seagrass beds recover more quickly from scarring.
This project is funded through a grant from the National Oceanic and Atmospheric Administration. Partners on this project include the North Carolina Coastal Federation, the North Carolina Aquarium at Pine Knoll Shores, and citizen volunteers.