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One might think that a person who joins an oyster-centered research project must have a lot of knowledge about oysters, really love them, or understand their role in aquatic ecosystems. However, save the fact that I didn’t like to eat them, I knew almost nothing about oysters before starting this project. It wasn’t until our fall lecture series that I began to understand how cool these creatures are. They filter water, construct their own habitat by building on top of one another, and provide homes for other species! With each class, I could feel myself getting more jazzed about oysters and wanted to take this opportunity to investigate them and their role in the ecosystem more deeply.
After seeing an oyster reef in person, I knew that oysters use the buddy system. While not all oysters are reef-forming, eastern oyster around my home in North Carolina, called Crassostrea virginica, cluster into reefs.Clustering is crucial to oysters’ survival, since it protects them from predators and enables them to reproduce most efficiently. To build stronger colonies, oysters grow on top of one another. However, since the top oyster smothers and kills the lower one, a conflict arises between each oyster trying to stay alive and the overall goal of building a robust colony.
Reef-building oysters have a bipartite or two-phased lifecycle, spending one life phase floating in the water as larvae and the other rooted on the reef as mature oysters. In the first phase of their lifecycle, larvae use a mixture of cues to find suitable habitat. For instance, to establish a reef, larvae must move from floating to resting by binding on a hard substrate, like old shells, rocks, or a pier. While floating, larvae use an appendage called a foot to search for such a substrate. Once larvae have located a suitable place, they bind to it by secreting a glue and undergo a complete internal anatomy metamorphosis. After this process, they are referred to as spat and continue to grow, ultimately becoming the mature oysters we recognize.
Aside from substrate, larvae also show preference for other environmental factors like salt concentration and oxygen exposure levels. Larvae prefer a salinity of 10-15 parts per thousand (ppt), which is between the salinity of river water (5ppt) and seawater (35 ppt). Oysters are unable to survive at low salinities, and, while they can live in full ocean water, the higher salinity brings predators and parasites that cause oyster death. Depth of a reef governs oxygen exposure for oysters. As shown in a study out of UNC Chapel Hill, reefs need at least 5% daily aerial exposure, or they can die. Considering these salinity and depth preferences is key for restoration so that researchers construct reefs with conditions that maximize their potential for success.
After reefs have formed, what do they do for their environment? Ecologically, oyster reefs support fouling organisms like mussels, barnacles, and sea anemones by providing a hard substrate on which they can reside. Reefs’ structural complexity also creates refuge from predators and nursery grounds for fish, invertebrates, and shellfish.
In addition to their ecological roles, oyster reefs provide valuable ecosystem services. While filter feeding to remove phytoplankton for consumption, oysters purify water by removing suspended solids and nitrogen compounds. A single oyster can filter up to 50 gallons of water each day! Without excess nitrogen, the ecosystem is at much lower risk for oxygen-depleting algal blooms and eutrophication. Removed contaminants are then bundled and excreted by the oysters, becoming food for other organisms, helping build up the reef substrate, and increasing denitrification through interactions with micro-organisms. Physically, the structure of reefs protects the shoreline from storms and tides, decreasing erosion. Reefs also are hot spots for many commercially valuable species like blue crab, flounder, shrimp, spot and speckled trout. According to NOAA Fisheries, oyster production alone was worth $234 million in 2015!
While I only scratched the surface of the intricacies of oyster reef ecosystems, I have an increased appreciation for their function and why it is important it is to preserve their biodiversity. Now, I am even more excited to be a part of a project that is working to understand and protect a species that is so fundamental to environmental health and to be doing it in my home state of North Carolina.
Post by Avery Indermaur, Bioacoustics team
References
Fodrie,F. J., Rodriguez, A. B., Baillie, C. J., Brodeur, M. C., Coleman, S. E.,Gittman, R. K., … Linquist, L. N. (2014). Classic paradigms in a novelenvironment: inserting food web and productivity lessons from rocky shores andsaltmarshes into biogenic reef restoration. Journalof Applied Ecology, 51, 1314-1325.
NOAAFisheries. (n.d.) Oyster Reef Habitat. Retrieved from https://www.fisheries.noaa.gov/national/habitat-conservation/oyster-reef-habitat.
NorthCarolina Coastal Federation. (n.d.) Food, Filter, and Fish Habitat-- what’s notto love? Retrieved fromhttps://www.nccoast.org/protect-the-coast/restore/oyster-habitat/.
Silliman,B. (2018). Lecture on Marine Ecosystems: Oyster Reefs. Personal Collection ofB, Silliman, Duke University, Durham NC.
