Measuring carbon and nitrogen bioassimilation, burial, and denitrification contributions of oyster reefs in Gulf coast estuaries
The eastern oyster (Crassostrea virginica) and the reefs they create provide significant ecosystem services. This study measured their possible role in nutrient mitigation through bioassimilation, burial, and oyster-mediated sediment denitrification in near-shore shallow water (< 1 m water depth) and deep-water (> 1 m water depth) oyster reefs in Louisiana. Nitrogen (N) and carbon (C) in shell and tissue differed by oyster reproductive status, size, and habitat type. Changes in tissue percent N and C post-spawning combined with significant reductions in tissue dry weight from the release of gametes, resulted in 20 and 46% reductions in tissue N and C load (mg), respectively, for a 100-mm oyster. Oyster reefs did not enhance burial rates, with burial range rates estimated at 1.4–2.6 g N m−2 year−1, and 26.9–43.8 g C m−2 year−1. Closed-system ex situ incubations indicated net denitrification in all habitat types studied, with the highest rates exceeding 600 µmol N m−2 h−1 during the summer, but no enhancement attributable to oyster reefs specifically. Within the highly productive, organic-rich wetland complex systems of coastal Louisiana, oyster reefs were not associated with enhanced denitrification, likely due to the organic-rich setting, and redundant supplies of organic nitrogen and carbon from adjacent marshes. Context remains critical in determining ecosystem provision of habitats, and efforts to extrapolate and predict nitrogen removal across locations necessitates consideration of local conditions. Considering the large extent of reefs and oyster production across coastal Louisiana, oyster habitats may still contribute to N and C mitigation, but their unique contribution likely comes from bioassimilation, and removal of the oysters from the system.
This work was funded through the Coastal Science Assistantship Program, through Louisiana Sea Grant and the Coastal Protection and Restoration Authority of Louisiana, as well as the Louisiana Department of Wildlife and Fisheries through the U.S. Geological Survey Louisiana Fish and Wildlife Cooperative Research Unit. Thanks to Dr. Chris Swarzenski for comments on an earlier version of this manuscript. Early discussion with Drs. Bryan Piazza and Michael Piehler contributed to the development of this project. Input and discussion with Drs. Austin Humphries, S. Ayvazian and Boze Hancock informed this work. Many thanks to Robert Twilley, Edward Castañeda, Andy Nyman, Jerome La Peyre, John White, Mike Kaller, Brett Collier, Kristy Capelle, Romain Lavaud, Christian Flucke, Songjie He, Scott Harlamert, Steven Madere, Jay Curole, and Tommy Blanchard for their help and expertise. Data are available through MKL. Reviews from three anonymous reviewers significantly improved this manuscript. Any use of trade, firm, or product names is for descriptive purposes only and does not imply endorsement by the U.S. Government.
Compliance with ethical standards
Conflict of interest
The authors declare that they have no conflict of interest.
All applicable international, national and/or institutional guidelines for sampling, care and experimental use of organisms for the study have been followed.
- Freeman AM, Roberts HH (2013) Storm layer deposition on a coastal Louisiana lake bed. J Coast Res 29:31–42Google Scholar
- Heffner L (2013) Responses of nitrogen cycling to nutrient enrichment in New England salt marshes over an annual cycle. PhD, University of Rhode Island, USAGoogle Scholar
- Henriksen K, Rasmussen MB, Jensen A (1983) Effect of bioturbation on microbial nitrogen transformations in the sediment and fluxes of ammonium and nitrate to the overlying water. Ecol Bull 35:193–205Google Scholar
- Henry KM (2012) Linking nitrogen biogeochemistry to different stages of wetland soil development in the Mississippi River delta, Louisiana. MS thesis, Department of Oceanography and Coastal Sciences, Louisiana State University, Baton Rouge, LAGoogle Scholar
- Howarth R, Anderson D, Cloern J, Elfring C, Hopkinson C, Lapointe B, Malone T, Marcus N, McGlathery K, Sharpley A, Walker D (2000) Nutrient pollution of coastal rivers, bays, and seas. Issues Ecol 7:1–16Google Scholar
- LDWF. Louisiana Department of Wildlife and Fisheries. 2013. Oyster stock assessment report of the public oyster seed areas of Louisiana. Oyster data report series 19. Baton Rouge, LAGoogle Scholar
- Newell RIE, Fisher TR, Holyoke RR, Cornwell JC (2005) Influence of eastern oysters on nitrogen and phosphorus regeneration in Chesapeake Bay, USA. In: RiF D, Olenin S (eds) The comparative roles of suspension feeders in ecosystems, vol 47. NATO science series IV—earth and environmental sciences. Springer, Dordrecht, The Netherlands, pp 93–120CrossRefGoogle Scholar
- R Core Development Team (2015) R: a language and environment for statistical computing. R. Foundation for Statistical Computing, Vienna. https://www.R-project.org
- Seitzinger SP (1988) Dentrification in freshwater and coastal marine ecosystems: ecological and geochemical significance. Limnol Oceanogr 33:702–724Google Scholar
- Smith RP (2009) Historic sediment accretion rates in a Louisiana coastal marsh and implications for sustainability. Department Environmental Sciences, University of Louisiana, LafayetteGoogle Scholar
- Valiela I, Foreman K, LaMontagne M, Hersh D, Costa J, Peckol P, DeMeo-Anderson B, D’Avanzo C, Babione M, Sham CH, Brawley J, Lajtha K (1992) Couplings of watersheds and coastal waters: sources and consequences of nutrient enrichment in Waquoit Bay, Massachusetts. Estuaries 15:443–457CrossRefGoogle Scholar
- Vitousek PM, Aber JD, Howarth RW, Likens GE, Matson PA, Schindler DW, Schlesinger WH, Tilamn DG (1997) Human alteration of the global nitrogen cycle: sources and consequences. Ecol Appl 7:737–750Google Scholar