Oysters in an Eastern Estuary

Authors

  • Timothy J. Hoellein,

  • Chester B. Zarnoch


Figure Photo 1.

Eastern oysters (Crassostrea virginica) were deployed at three densities in mesh cages suspended above sand-filled boxes at four sites in Jamaica Bay, New York City. Controls consisted of boxes with empty cages attached. (A) All boxes (N = 20 per site) were attached to a trot line between two cinderblocks, and deployed subtidally. Boxes were collected bimonthly by hand and walked to the shore. (B) We counted oyster mortality, replaced dead individuals, and sampled sediment for carbon and nitrogen dynamics. (C) Mott's Basin was moderately eutrophic and adjacent to a natural-gas-burning power plant. Photo credits: Timothy Hoellein and Chester Zarnoch.

Figure Photo 2.

Our four study sites spanned a nutrient-loading gradient in eutrophic Jamaica Bay. The Jamaica Bay Wildlife Refuge is shown above. Note the skyscrapers of lower Manhattan on the central horizon. Photo credit: Emily Driscoll/Stavros Basis.

Restored oyster reefs may promote denitrification (i.e., anaerobic respiration of nitrate to dinitrogen gas, N2), via benthic deposition of carbon (C) and nitrogen (N)-rich wastes (biodeposits). This has not been measured in eutrophic ecosystems, where denitrification is a potential oyster-mediated ecosystem service. We tested oysters' influence on sediment C and N dynamics in eutrophic conditions. Oysters increased sediment organic C at three of four study sites. Oysters did not affect sediment N transformations, likely because none were driven primarily by C availability. The article presents a diagram to illustrate the context dependence of oysters' role in sediment N dynamics in oligotrophic and eutrophic ecosystems.

Figure Photo 3.

We expected that oyster biodeposits would increase sediment organic matter, ammonification, nitrification, and denitrification potential. (A) Oyster biodeposits include feces (upper right) and pseudofeces (lower left). Feces are excreted following digestion, and pseudofeces consist of filtered particles that are not ingested, but are covered in a mucilaginous mixture and rejected. (B) Students measure denitrification potential (DNP) on sediment from control boxes, and boxes from low, medium, and high oyster density. Oysters increased sediment organic matter, but did not have an effect on DNP because DNP was not primarily limited by carbon availability. Photo credits: Timothy Hoellein.`

These photographs illustrate the article “Effect of eastern oysters (Crassostrea virginica) on sediment carbon and nitrogen dynamics in an urban estuary” by Timothy J. Hoellein and Chester B. Zarnoch, tentatively scheduled to appear in Ecological Applications 24(2), March 2014. doi: http://dx.doi.org/10.1890/12-1798.1

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