How SAV-vy are Farmed Oysters?

By BRADY BLACKBURN

Posted Nov. 10, 2015

Brady Blackburn is a junior the University of North Carolina at Chapel Hill. He is majoring in environmental studies and focusing on science communication.

Wild oysters filter particles that may be detrimental to water quality out of the water as they feed, benefiting their surrounding environment. The potential services of farmed oysters, however, are still largely unknown.

Many studies of oyster farming, or oyster aquaculture, suggest that the practice prevents submerged aquatic vegetation, also known as SAV, from growing.

These grasses provide a critical habitat in sounds and estuaries for many aquatic species. In North Carolina, the state will not issue leases for shellfish farms unless there is no SAV — current or historical — present. The U.S. Army Corps of Engineers, who administers this regulation, plans to review the rule next year.

I have lived in Manteo, N.C., for about two months to study with nine other undergraduate students from the University of North Carolina at Chapel Hill. Along with taking environmental science classes at the University of North Carolina Coastal Studies Institute, we are studying oyster aquaculture and how its environmental benefits differ from those provided by wild oyster reefs in the Albemarle-Pamlico Estuarine System.

Part of our research is focused on how aquaculture affects SAV growth. A majority of the studies that suggest aquaculture has a negative impact on SAV have only looked at the areas directly under hardware — floating racks and bags that hold oysters suspended in the water. They haven’t studied any other locations, such as the boat lanes in between the hardware or the perimeter around the facilities.

Joey Daniels, who runs Bodie Island Oysters, the aquaculture facility we are studying, suggested to us that his facility’s hardware actually is beneficial to SAV growth.

He told us that their gear — the racks, bags, lines and poles — all catch uprooted SAV as it floats by, allowing it to drop seeds right there at his facility instead of floating on into deeper waters where it can’t grow.

After four different sampling days on the water (and a fifth attempt spent caught in a massive rainstorm), we are now putting together and analyzing our data. We haven’t made any concrete conclusions yet.

However, we have found SAV both in and around Daniels’ aquaculture facility. Most of the thick patches have been in the boat lanes within the facility and around its perimeter.

Along with our SAV study, we are comparing various water-quality components at each of our sites. We are estimating light-extinction ratios to determine how deep light can penetrate into the water. Deeper light penetration indicates better water quality, as well as better habitat for SAV.

In addition, we are measuring phytoplankton in the water by calculating concentrations of chlorophyll, a pigment in photosynthesizing organisms. The relationship between phytoplankton presence and water quality is less clear, and I will be discussing this relationship in my next post.

Along with all of this, we are conducting interviews with members of the local community to gain an understanding of their perceptions of oyster aquaculture and the estuary in general.

To learn more, check out my previous blog post, “Studying Oysters in an Estuarine Environment.” I will also be discussing all of the components of our study in blog posts throughout the rest of this semester, so stay tuned!