The Eastern Oyster (Crassostrea virginica) is our most valuable coastal resource, providing critical habitat for fish and invertebrate species, shoreline stabilization, water quality enhancements and numerous other ecological functions. The compounding effects of increased fishing pressure in smaller areas, hurricanes, tropical storms, droughts, flood events and unscrupulous actions by some within the commercial oyster industry have resulted in unprecedented destruction and loss of our public oyster reefs. Here are just a few reasons why oysters are so valuable to our marine ecosystems. Feel free to click on the literature cited to further review the supportive documentation.
General Information
Oysters are filter feeders, consuming phytoplankton (free-floating microscopic algae) and improving water quality while filtering the water for food. One oyster can filter more than 50 gallons of water in 24 hours. As generations of oysters settle on top of each other and grow, they form reefs that provide structured habitat for many fish species and crabs.
Oysters are a keystone species, meaning that they provide important ecological services to their environment.
Oysters are the building blocks in one of the most important benthic communities and are the only natural hard bottom found in Texas.
Oysters and their subsequent reef systems play critical roles in our coastal ecosystems. They provide habitat for a variety of aquatic species, serve as organic biomass for coastal food webs, stabilize shorelines, reduce coastal erosion and sedimentation, and improve water quality by serving as filter feeders.
303 different marine aquatic species have been identified that use oyster reefs for habitat, refuge, and food (Wells 1961). Furthermore, oyster reef habitat supports nearly 4.5 times the aquatic biomass found in seagrass beds and roughly 11.5 times the aquatic biomass found in marsh edge habitat (Glancey et al. 2003).
Beck et al (2011) and Lotze et al (2006) estimate that only 15% of the world’s oyster reef habitat are remaining. We must do what we can to protect this critical habitat and have a sustainable oyster fishery.
Oyster reefs provide important habitat for recreational and commercial valuable species (Coen et al 2007, Lenihan et al 2001, Peterson et al 2003, Grabowski et al 2005).
We, as a state, take extreme measures to protect our seagrasses and spartina marshes on our coastal shorelines. We establish state scientific areas to protect seagrass and maintain fish habitat, and we require that spartina marsh be restored if any is disturbed by coastal development. Why would we not offer similar protections and considerations for our oyster reefs, which have been proven to provide unique services for our coastal ecosystems?
Ecosystem Services Provided by Oysters
Oysters provide the following ecological services:
- Water Quality Improvement – remove chlorophyll a, reduce turbidity, denitrification, increase benthic algal or pseudofecal production, bacterial biomass removal
- Stabilize shorelines
- Sequester Carbon
- Increase fish production
- Provide habitat for epibenthic fauna
- Diversify the landscape and create synergies among habitats
- Increase oyster reef production
Peterson et al (2003) estimate that 10m2 (2.5 acres) of a restored or unfished oyster reef in the southeast United States would be expected to yield an annual additional of 2.6 kg (6lbs) of production of fish and large mobile crustaceans for the functional lifetime of the reef.
Zimmerman et al (1989) in a document prepared for TPWD in 1989 stated that oyster reef and marsh habitats were significantly more utilized than bare mud bottom by coastal infauna and epifauna (small organisms living either attached to or under a surface). There is a high attractive value for reefs and marsh. The notion that oyster reef and salt marsh support unique community assemblages is supported, and neither can be viewed as an alternative for the other. (Infauna and epifauna are important foods for juvenile shrimp, blue crabs, and fishes.)
The economic value of oyster reef services, excluding oyster harvesting, is between $5,500 and $99,000 per hectare per year and that reefs recover their median restoration costs in 2–14 years. In contrast, when oyster reefs are subjected to destructive oyster harvesting, they do not recover the costs of restoration (Dollar Reef in Galveston for example). Shoreline stabilization is the most valuable potential service, although this value varies greatly by reef location. Quantifying the economic values of ecosystem services provides guidance about when oyster reef restoration is a good use of funds. (Grabowski et al 2012).
We estimate the average annual value of services provided by restored and protected oyster reefs that ranges from $10,325 to $99,421 per hectare, depending on where the restored reef is located and the suite of ecosystem services that the restored reef provides. Both of these measures are at least an order of magnitude greater than the commercial value derived from harvesting the oysters produced by degraded reefs. (Grabowski et al 2012).
The combined Minor Bay closures and 300-ft buffer = 3,189.4 Ac or 6.6% of total Texas oyster habitat. The ecosystem services and economic values of these closures is valued between $41.5M – $778M.
Oyster Size and Spawning Information
The number of gametes released during each spawn is directly correlated with oyster size and gonadal development (Davis and Chanley 1956, Galtsoff 1964, Thompson et al. 1996). Among oysters of the same size, variability of fecundity is due primarily to differences in the physiological condition of the oysters (Galtsoff 1964).
Galtsoff (1964) estimated a range of 10-20 million eggs per female per spawn and as many as 100 million eggs produced per female in a season. The number of eggs is proportional to the size of the individual (Davis and Chanley 1956).
Thompson et al. (1996) reported fecundity estimates from 2 million eggs (4 cm/1.5 inch adult) to 45 million eggs (7 cm/2.75 inch adult). Thus, allowing more oysters to reach legal size can significantly increase the amount of gametes released into the water column.
Although there are no estimates on the densities of broodstock required to ensure spawning and fertilization success, Galtsoff (1930) estimated that more than 60,000 oysters (> 8 cm shell length) per hectare (2.5 acres) are needed for a successful spawning bed.
In the lower coast, 37 cases were made for undersize oysters in Feb 2017. 68% of the cases had greater than 30% undersize oysters. This is an alarming statistic and proves that there are deliberate efforts to keep and sale undersized oysters.
700 cases were made by TPWD game wardens for undersized oysters from 2012-2017.
Area Closures – Oyster Sanctuaries
A sanctuary will offer protection for oyster broodstock. The larvae produced by broodstock within these sanctuaries will be carried by currents and tides to surrounding areas, seeding nearby public waters and serving as a source for sustainable oyster harvests in the future.
The Maryland DNR has a successful oyster sanctuary program. They state that both recreational and commercial fishing benefit from improved oyster bar habitat in sanctuaries because oyster bar habitat provides critical habitat to blue crabs, striped bass, white perch and other important finfish species. Oysters within sanctuaries are also expected to increase the abundance of adult oysters whose larvae are expected to settle not only within the sanctuary, but also on public shellfish fishery areas in the vicinity of the sanctuaries.
Both Maryland and Virginia have oyster sanctuaries, which are closed to harvest indefinitely. In Maryland, sanctuaries cover about 9,000 acres, or about 24% of the mapped oyster bar habitat. There are several oyster sanctuaries in the Potomac River, which is mostly managed by Maryland.
https://chesapeakebay.noaa.gov/fish-facts/oysters
http://dnr.maryland.gov/fisheries/Pages/oysters/sanctuaries.aspx
North Carolina has 392 acres identified as oyster sanctuaries and has plans for expanding their sanctuary program. http://portal.ncdenr.org/web/mf/habitat/enhancement/oyster-sanctuaries
Area Closures – Intertidal oyster reefs
Our intertidal reefs have to be protected from commercial harvest. The greatest ecological service provided by oyster reefs is shoreline stabilization. Reefs that provide effective erosion protection potentially provide a value that dwarfs both restoration costs and the value of all other ecosystem services (Grabowski et al 2012).
Intertidal reefs are critically important to Submerged Aquatic Vegetation (SAV) habitat or potential SAV habitat: An oyster reef that is located near SAV or near an area where the presence of a high number of oysters could promote SAV development would have a higher potential to benefit this important habitat both by improving water quality and by baffling wave energy (Grabowski et al 2012).
Because of the topography and shallow water depth of our coastal shorelines, oyster reefs within these zones are not able to build vertically. A typical shoreline reef may only be a few inches in height, making them highly vulnerable to intensive commercial harvest.
The Harte Institute in Corpus Christi has conducted numerous studies on the importance of shallow subtidal oyster reefs in Texas over the past several years. They have proven that that these areas support extraordinarily high densities, over an order of magnitude greater, of ecologically and economically important fisheries than the nearby deeper reefs. The juxtaposition of these areas within the habitat mosaic – typically surrounded by other habitat types and free of harvest, cause these areas to be unusually productive. These areas are much more productive than deeper open water reefs (Stunz et al. 2010).
Helpful Articles
“The Texas Oyster Industry Is Now a Shell of Its Former Self” – by Gwendolyn Knapp, Houstonia
State considers life raft for beleaguered oysters – by Shannon Tompkins, Houston Chronicle
Survey of oyster bottoms in Matagorda bay, Texas – by H. F. Moore
Dredging up a Texas Squabble – by Edwin Shrake, Vault.SI.com
Literature Cited
Buzan et al. 2015. Saving buried oysters.
Carson, Henry S. 2010. Population connectivity of the Olympia oyster in Southern California.
Colden et al. 2017. Reef height drives threshold dynamics of restored oyster reefs.
Galtsoff, R.S. 1930. The Fecundity of the Oyster. Science. Vol. 72. Issue 1856: 97-98.
Galtsoff P.S. 1964. The American Oyster Crassostrea virginica Gmelin. Fish. Bull. 64: 421-425.
Thompson, R.J., R.L.E. Newell, V.S. Kennedy and R. Mann. 1996. Reproductive processes and early development. The Eastern Oyster Crassostrea virginica. Maryland Sea Grant College, University of Maryland, College Park, MD, pages 335-370.
