Oysters of New York

Denitrification heroes?

by Liza Lester, ESA communications officer

The dense urban life of Queens surrounds Jamaica Bay, NY, where Timothy Hoellein and Chester Zarnoch measured the effect of oysters on the nitrogen cycle. Can oysters help remove an excess of the nutrient from the bay? Hoellein and Zarnoch fixed cages of oysters below the low-tide line (top left) and returned twice a month to sample carbon and nitrogen dynamics in the sediment. A natural-gas-burning power plant flanked the moderately nutrient-loaded study site at Mott’s Basin (right panel). Oysters once clustered thickly in Hudson River estuaries, but disappeared in the twentieth century under the combined effects of harvesting, habitat loss, and pollution, especially sewage. Public interest in oyster restoration and ecosystem services has opened many new research questions. Credit, Timothy Hoellein and Chester Zarnoch.

The January 2014 ESA Bulletin is out, with a photo gallery illustrating Timothy J. Hoellein and Chester B. Zarnoch’s preprint in Ecological Applications, “Effect of eastern oysters (Crassostrea virginica) on sediment carbon and nitrogen dynamics in an urban estuary” tentatively scheduled to appear in the March, 2014, issue.

Oysters pull nitrogen, phosphorus, and carbon from the water and deposit them in solid form on the bottom of the bay. Water running off of cities and agricultural fields generally delivers an over-abundance of these nutrients to the coast, feeding algae blooms and creating low oxygen “dead zones.” Microbes living in estuary sediments remove nitrogen from the water by converting it to gas form. They also fix nitrogen as inorganic ammonium and pass it along to aquatic plants and animals. Oysters may be helping to move the nitrogen-removal process along by capturing nitrogen in their poop and in ejected packets of indigestible particles (pseudofeces), and delivering it to soil microbes.

To test this possibility in an urban estuary with a high nutrient load, Hoellein and Zarnoch planted oysters in wire cage boxes at four locations in Jamaica Bay, New York City, where oysters once thrived. A keystone species prior to the twentieth century, eastern oysters are now functionally extinct in the Hudson, but water quality has improved to the point that they have a chance of coming back. Hoellein and Zarnoch placed their experimental oysters across an increasing gradient of nitrogen concentration, from Floyd Bennett Field at the bay’s inlet, to Spring Creek, which flows past a sewage treatment plant.

They did not observe a net effect of oyster presence on nitrogen cycling, though the oysters did increase the organic matter on the estuary floor. Hoellein and Zarnoch argue that oysters could affect nitrogen gas production in this nutrient rich city estuary, given the right combination of nutrients and habitat characteristics, and that other ecosystem services provided by oysters, such as particle filtration, are also likely to be context-dependent.

Also in this issue of the Bulletin:

• appointment of the Editor-in-Chief of a new joint journal of ESA and the Ecological Society of China
• an educational agenda “Into the Mind of Nature” and sustainability
• report on ESA’s Scaling Up workshop

& much more.