The Westport River Watershed Alliance (WRWA) is working with the Coastal Systems Program (CSP) UMass Dartmouth (SMAST) on a project funded by a grant from the US EPA Southeast New England Program (SNEP) for Coastal Watershed Restoration. The UMass Dartmouth initiative, led by Dr. Brian Howes and Dr. Roland Samimy at SMAST's Coastal Systems Program, is utilizing Cockeast Pond as a natural laboratory to measure how oysters improve water clarity and potentially reduce elevated nitrogen levels which indirectly destroy fish and other marine wildlife habitats.

Last September over ~30,000 oysters were placed at four different locations in Cockeast pond in 15 floating bags and 4 bottom cages, constructed of high quality, industrial grade vinyl coated wire. After a few months, SMAST scientists sunk the oysters in deeper water to overwinter in the pond, they seem to be surviving well.  Survival/mortality was quantified at each location and a sub sample of oysters from each bottom cage was measured, weighed and brought back to SMAST for analysis of nitrogen content in the meat and shells.  This initial small scale deployment was a simple survivability test to determine if Cockeast Pond waters would be supportive of a large scale oyster deployment in the summer of 2017. By the end of June 2017, activities will gear up again as the full scale experiment will begin and involve adding around 500,000 oysters over approximately 60 square meters (less than 1% of the total pond area).

The project is using oysters grown by Westport's own  Riptide Oysters. The SMAST team is planning to deploy the oysters in one main location within Cockeast Pond; generally the southwest quadrant of the pond south of the large rock the middle of the pond.  A secondary location was selected as necessary on the north-east side of pond. As a precursor to this work permits and permissions were secured from Army Corps of Engineers, the MA Division of Marine Fisheries, and the Town of Westport Marine Services Director.

WRWA's role in this project is multi-faceted and will focus on both science and outreach. We will also be involved in the set-up of the various oyster gear as well helping with the deployment and maintenance of the oysters. Additionally, WRWA is helping with community outreach by distributing information to residents regarding the project and promoting its results on our website and social media, so stay tuned for updates.

Why Do the Study?

We know oysters are filter feeders; they remove particles from the water that contain nitrogen, primarily in algae (phytoplankton), and use it to build their tissues and shells or move it to bottom sediments in their biodeposits. Once the nitrogen is in the sediments, microbes may break it down and release nitrogen gas into the atmosphere, a process called denitrification, removing nitrogen from the estuary. Also, all the nitrogen that is in any oysters that are harvested is removed from the system as well. The oysters in the experiment will not be harvested, but transferred to areas to depurate (clean-out) as they reach specific size limits with the hope that after the four year experiment is completed, an historic oyster bed in the East Branch of the Westport River will have been repopulated.

Not as well understood, however, is the amount of nitrogen that is either sequestered via deep burial in bottom sediments or returned to the atmosphere via denitrification. Determining rates of sequestration and denitrification is much more difficult than estimating nitrogen removal by harvest.

Data collected so far on denitrification associated with either intensive oyster aquaculture or restored oyster reefs show much greater variability than data on nitrogen content of shells and tissues. Data from past studies suggest that restored oyster reefs significantly enhance denitrification rates, however the degree of enhancement is highly variable. Denitrification rates vary with season, tidal regime, environmental conditions, oyster biomass density, and other unidentified factors, possibly including differences in microbial communities. That is one reason why this study was granted funding. These additional studies are needed to better understand the sources of this variation before assigning a value to the nitrogen removal capacity of oyster reefs attributable to denitrification. Scientists know little about nitrogen sequestration via deep burial; to date, no measurements of nitrogen burial rates associated with oyster reefs or oyster aquaculture have been published.

This research on oysters may help decision makers and citizens across the southeastern Massachusetts region understand the role of oyster reefs as natural capital, thus opening the door to greater investments in nature-based restoration techniques. This is more than just revitalizing an industry, it is the inherent ecological values of the oysters, including improving water quality and protecting shorelines we promote while also maintaining the unique cultural dimension of the region.  Understanding the efficacy of restored oyster populations on improving nutrient related water quality is but one of many strategies that may be considered by the Town of Westport as it develops a holistic nutrient management plan for the watershed to the Westport River estuary.  It does not obviate or diminish the importance of nutrient load reductions to improve water quality in Cockeast Pond or the greater Westport River estuarine system. 

If you would like to learn more contact Roberta Carvalho, WRWA Science Director at  [email protected].