Measures of a Successful Oyster Reef

Results of a Stockton University study measuring the water quality and habitat impacts of the Tuckerton Oyster Reef.
Red beard sponge and other encrusting organisms growing on oyster shells from the reef. (Photo by Dr. Christine Thompson)

Article by Dr. Christine Thompson, Assistant Professor of Marine Science, Stockton University

In the late 1800s, oysters were estimated to span over twelve thousand acres of the Barnegat Bay. We can estimate that these oysters could filter more than three times the volume of Barnegat Bay in one hour! But by the mid-1900s, oyster reefs were decimated due to overfishing and environmental changes.

The Tuckerton Oyster Reef in Barnegat Bay was established in 2016 as the first oyster restoration project in the southern area of Barnegat Bay, and it is now the largest oyster restoration site in the bay. In those six years, I’ve been researching how the various types of oysters planted at the site have been growing.  

It is easy to talk about the reef in terms of numbers: how many bushels of oyster shell were planted (2,700), how much spat-on-shell went out (45 million), or how many acres of habitat restored (two and growing). But it is not quite as easy to measure the impacts of the reef: How many of the oysters survived and reproduced to sustain the population? How much water are the oysters filtering? How many other species have benefited from the new habitat?

To get at these numbers, the Barnegat Bay Partnership funded Stockton University in 2019 to study how the Tuckerton Reef impacts water quality and habitat, and to create a baseline for success to compare with other restoration projects. 

Success metric 1: Sustainable populations

You can’t have an oyster reef without oysters. But what is the minimum sustainable number of oysters to make it a “reef”? Past research estimates that number to be around 10-15 oysters per square meter. That doesn’t seem like many. It is often dependent on location – oysters can grow bigger at higher salinities.

In an area like Barnegat Bay, where we plant oysters directly on the bottom, we end up with large oysters with lower densities. This study found that oysters planted in 2016 maintained this minimum density for four years, but by 2020 had fallen below this threshold. Sampling for density can inform us when certain areas of the reef could use an extra “boost” of spat on shell.  

We found that the densities at each site are dependent on the shell types used and the planting method. In 2019, oysters were planted over a smaller area, resulting in greater densities; in 2020, the oysters were spread out more and had lower densities. Initial survivorship was higher in 2020, when recycled shell was primarily used as the substrate. We also discovered that planted oysters grew better on whelk shell compared to oyster shell (don’t tell the shell recyclers this!); however, the larvae preferred to settle on the oyster shells.

Success Metric 2: Water quality improvement

Stockton student collecting water quality data at the Tuckerton reef. (Photo courtesy of Stockton University)

In total, the estimated filtration rate for the Tuckerton reef was about 1.1 million liters per hour, or 290,000 gallons. That ends up being almost 7 million gallons per day – or 10 Olympic-sized swimming pools of water.

Oysters are natural water filters; they obtain food by filtering phytoplankton and suspended organic material from the water column. In the Barnegat Bay, there is an excess of both phytoplankton and suspended organic material, which oysters can help reduce through filter feeding. The footprint of the oyster reef (1 acre in 2020) is very small compared to the size of Barnegat Bay – about 0.005%. Only once during our two years of sampling did we observe clearer water over the reef compared to the control. It was exciting and worthy of an Instagram post, but it was not the norm.

What we can do, however, is estimate the filtration capacity of oysters on the reef. The rate that oysters filter water depends on temperature, salinity, suspended sediment concentrations, and oyster size and density. We measured temperature, salinity, and suspended sediment monthly on the reef. Next, we input these values into equations that estimated the filtration rates based on oyster size and density.

This allowed us to see the filtration rates for each planted area using water quality parameters. In total, the estimated filtration rate for the Tuckerton reef was about 1.1 million liters per hour, or 290,000 gallons. That ends up being almost 7 million gallons per day – or 10 Olympic-sized swimming pools of water.

The numbers sound large, but when we think about the WHOLE BARNEGAT BAY, there is a lot of water to filter (about 31 billion gallons!). We estimate that it would take about 12.3 years for the 2020 reef to filter the water in the bay. Only ten more years to go!

Success Metric 3: Habitat enhancement

Overall, there were 40-60% more species found on the reef sites compared to an unrestored, bare-bottom area.

Another important ecological service that oyster reefs provide is habitat. Many fish and invertebrates see an oyster reef as a place to live and lay eggs, hide from predators, or find a tasty meal. We monitored fish and crab species around the reef using traps three times in 2019 and 2020. The most common visitors to the traps at both sites were black sea bass (Centropristis striata), oyster toadfish (Opsanus tau), spider crabs (Libinia emarginata), and blue crabs (Callinectes sapidus). Only oyster toadfish was found more frequently on the reef sites (not a surprise considering the name!).

However, many less abundant species were more commonly found on the reef sites – burrfish (Chilomycterus schoepfi), sea horses (Hippocampus erectus) and tautog (Taugoa onits) to name a few. Overall, there were 40-60% more species found on the reef sites compared to an unrestored, bare-bottom area. We also found that the older plantings on the reef still supported a diverse assemblage of species despite having lower densities of live oysters.

Success Metric 4: Human element

Although the Tuckerton Reef may not be as impressive of a scale as some of the restoration projects in other states, this project has demonstrated we can work with what we have and create a habitat for Barnegat Bay species that can be maintained. We plan to keep adding shell to this site, using the monitoring data to tell us which areas need enhancement. We’ve seen increases in naturally settling oysters both on this site and around the bay.

Partners meet on the reef site to watch oysters planted onto the reef in 2020. (Photo by Susan Allen)

More people who live around the bay or visit during the summer are being exposed to the benefits of oyster aquaculture and restoration through restaurant outreach programs and the Long Beach Township Marine Field Station in Holgate. Oyster restoration is now a solid part of the curriculum for Stockton University Marine Science undergraduates, many of whom get hands-on experience sampling oysters in class or doing summer research. We’ve expanded the potential for using oysters in designing natural infrastructure around Barnegat Bay to reduce flooding and storm surge.

Oysters are back in Barnegat Bay and here to stay!


Full Report: “Barnegat Bay Oyster Restoration 2021”

Follow the shell! – oyster recycling program

Tuckerton Reef website

Stockton Shellfish Lab Instagram

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