Mighty Mussels (and Oysters) are Cleaning Up Water Across the US

By on December 21, 2017
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Ribbed mussels held by researcher. (Credit: NOAA.)

Although we humans often overthink and over-engineer solutions to our problems, nature often presents us with more elegant fixes we can implement with relatively low effort and cost. The case of the humble bivalve proves this point nicely, and several projects across the US are deploying mussels and oysters to help improve water quality right now.

Ribbed mussels in the Bronx River

Since 2011, NOAA researchers have been working with ribbed mussels, Geukensia demissa, to explore their potential for removing excess nutrients like nitrogen from urban estuaries and improving urban water quality more generally. The ribbed mussels are part of an overall effort to improve the water quality in New York City’s Bronx River.

The ribbed mussels are anchored to a 20 x 20-foot raft that has lines for growing mussels hanging beneath it. This raft is in the Bronx River in an industrial area, not far from a sewage treatment plant and Hunt’s Point. Here scientists are able to monitor the water quality along with the condition of the ribbed mussels over time. A raft of this size that’s fully populated with ribbed mussels could clean about 350 pounds of particulate matter, such as soot and dust, from three million gallons of water, every day on average.

Native to estuarine habitats along the East Coast, ribbed mussels can efficiently filter bacteria, contaminants, nutrients, microalgae, and a variety of other particles from water. They are not eaten by humans, so eating absorbing contaminants isn’t a problem, and so long as they remain somewhere within their range, they are hearty enough to adjust from place to place as the water and nutrients change.

Julie Rose, an environmental biologist and research ecologist at the NOAA Fisheries Milford Laboratory, and Eve Galimany, a postdoctoral researcher from the Institute of Marine Sciences, CSIC of Barcelona, Spain comment on the choice of the ribbed mussel, a native to the east coast of the United States that is at home in an urban environment.

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Eve Galimany and Daphne Belfodil from the NEFSC’s Milford Laboratory monitor ribbed mussel feeding activities within the filtration apparatus. (Credit: NOAA.)

“One reason is that there used to be lots of ribbed mussels naturally growing all around New York City and other urban areas,” the scientists explain. “But as the cities have grown, most of the coastline that used to be ribbed mussel habitat has been lost to bulkheads, ports, and other waterfront infrastructure. With the raft, we are restoring some of the ecosystem functions that were once provided by historic ribbed mussel populations. Another interesting challenge in the Bronx was related to local bacterial contamination that is common in urban areas. High bacterial numbers meant that the shellfish could not be harvested from the Bronx for human consumption, but the poor taste of the ribbed mussel and the absence of a commercial market made the ribbed mussel a good candidate shellfish species. Also, ribbed mussels are used to environments with high amounts of particles in the water, that’s another reason why they were good candidates in the Bronx.”

Once the mussels are finally harvested, they can be used in animal feed or as fertilizer, recycling nutrients and avoiding waste generation.

“When the mussels are harvested they are removed from the local ecosystem and therefore wouldn’t be able to be eaten by other wildlife,” the researchers explain. “After harvest, the hope is that the mussels would be able to be recycled instead of ending up in a landfill. The end use would depend on the organic and metal contaminants in the tissue and shell. We found that contaminant concentration could be greatly reduced by growing mussels in the water instead of on the seafloor.”

In some cases, the presence of the filtered contaminants can even make the mussels more nutritious for livestock.

“If the tissue contaminants were still high in a particular location, it is possible that parts of the mussel could be used as supplements for plant-based fish feeds—like the omega-3 fatty acids in the mussel tissue for example or shells might be a calcium supplement for chicken to increase egg shell thickness,” the scientists clarify. “Researchers in Europe have studied the use of blue mussels for chicken and pig feed, and found that adding mussel meal as a supplement improved the quality of the feeds.”

Like so many other fruitful projects, this one took flight thanks to a collaboration between many stakeholders. As they look back on this work, Dr. Rose and Dr. Galimany point to the broad range of skill and tremendous effort from their team as primary factors in the project’s success.

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Tagging mussels in Puget Sound. (Credit: Puget Soundkeeper.)

“This project was only possible because of the forward-thinking folks in New York City and the NY State Office of the Attorney General who were seeking new and innovative solutions to water quality challenges in the urban environment,” assert the researchers. “The Bronx River Watershed Initiative that funded this work specifically sought out new approaches to improving the health of the Bronx River ecosystem. We had an amazing team, including Maine commercial mussel farmer Carter Newell, who installed the raft and harvested the mussels, and members of a local youth development organization, Rocking the Boat, who were in the water most days maintaining the raft and the mussels on it. NFWF program officer Lynn Dwyer helped us navigate the complicated permitting system, and various scientists from NOAA with different areas of scientific expertise enabled our team to explore biology, chemistry, and ecology as part of this project.”

Cape Fear Reef Building

Since the 1970s, the North Carolina Division of Marine Fisheries (NCMF) has been building artificial reefs in the Cape Fear River as part of its Artificial Reef Program. The latest installment of the project is now underway, and the NCMF along with the North Carolina Coastal Federation (NCCF) and the Carolina Beach State Park are building Artificial Reef (AR) 491 within a five-acre space just off the shoreline of the park in the Cape Fear River.

Ted Wilgis, an oyster restoration specialist for the NCCF, is working on AR 491.

“The one-acre initial construction is part of a five-acre project area for the artificial reef AR-491,” Wilgis explains. “The lead agency on the project, the NCMF, wants to give the initial construction some time to perform so they can evaluate it and make any needed adaptive management changes moving forward with the remaining four acres. This oyster restoration project is part of the greater Cape Fear plan, which is intended to increase oyster and fish habitat, and improve water quality in the Cape Fear River and the surrounding watershed, and throughout the North Carolina coast.”

The purpose of this reef and the others is to enhance recreational fishing, create oyster reef habitat, and improve water quality in the lower Cape Fear River. These artificial reefs achieve these goals in several ways.

“This five-acre spot for the project was chosen for its proximity to Carolina Beach State Park and its potential for creation of an oyster reef habitat,” Wilgis states. “Recreational anglers enjoy the shallow water surrounding the park. A nearshore, accessible artificial reef will improve fishing opportunities and serve as hard bottom habitat for finfish species, as well as the oysters. The reef’s structure itself will draw fish for feeding, breeding, and refuge.”

Once the river was home to many bivalves, but over time their habitats were destroyed. The project seeks to rectify that problem, and with it improve the quality of the river water.

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Cape Fear River. (Credit: By Blipperman (Own work) [CC BY-SA 3.0 (https://creativecommons.org/licenses/by-sa/3.0)

“The Cape Fear River was once home to expansive reefs, but after decades of deepening of the river, disease, loss of habitat, overfishing, pollution, and sedimentation, the local oyster population has declined severely,” explains Wilgis. “However, a large volume of floating oyster larvae still call the river home, and the artificial reef provides them with a place to attach and form new oyster reefs. Oyster restoration is critical for improving fish habitat and water quality. Every day, an adult oyster can filter as much as 50 gallons of water. Once the reef is populated with oysters, their filtering capacity will add in the removal of pollutants like sediment; excessive algae/plankton and the reef itself promotes the settlement of sediment out of the water column.”

Erosion is also a serious problem in this portion of the watershed, and the reef can help slow this process down.

“More feet of living shoreline will be added to the shores of the Cape Fear River in 2018,” Wilgis reveals. “There is also an existing living shoreline adjacent to the AR. The new AR will help to dampen waves and wakes before they reach the shoreline, reducing some of the erosive forces.”

Wilgis also explains how the reef improves the surrounding watershed’s overall health in multiple ways: “Oysters are a ‘keystone’ species in the lower Cape Fear estuary. They provide many ecosystem services. Adding more oysters and reef habitat will have many ecological and economic benefits to the system. It also stimulates people’s interest in the river and becoming more engaged in its stewardship.”

As the project continues, the research team will be monitoring not just water quality, but also waves and shoreline changes.

“The construction is being coupled with several monitoring projects including wave monitors and GIS mapping looking at shoreline change,” Wilgis clarifies. “Additional monitoring and study on sediment transport in the area and how the reef effects it will also be evaluated. We are working closely with geologists and marine biologists from UNCW on the project, monitoring and modeling.”

The Cape Fear artificial reef project is one of the most long-running and successful in the US, but as powerful as these bivalves are at removing contaminants, Wilgis reminds us that they need our help.

“Oysters and their reef habitat are incredibly important and they are facing local and global threats,” cautions Wilgis. “Locally, increased sedimentation and low dissolved oxygen are stressors. Globally, climate change and ocean acidification are challenging the oysters in terms of their ability to build their shells to seeing the salinity change in their local waters.”

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Apparatus to measure mussel filtration at the Bronx River site. (Credit: NOAA.)

Mussels measuring contaminants in Puget Sound

Just a few weeks ago, a new wave of volunteers braved the cold shore of the Salmon Bay region of the Puget Sound on a Friday night in December to help scientists install cages of mussels in the water. The mussels, secured to the sides of the cages, will help the scientists monitor the health of the local ecosystem as they filter contaminants out of the water, suspended near the bottom of the water.

The researchers will remove the mussels every 90 days to compare past records of contaminants with what the latest spate of mussels have trapped in the water. It’s critical to monitor over time this way, because static samples of water only provides a snapshot of what’s in the air and water at a specific moment.

Chris Wilke, Puget Soundkeeper and Executive Director of the Puget Soundkeeper Alliance, and Connie Sullivan, Puget Soundkeeper’s Science and Education Coordinator, explain their process.

“Here in Puget Sound, the Mussel Watch program is run by the Washington State Department of Fish and Wildlife,” the researchers explain. “They select the sites and organize local groups like Puget Soundkeeper to host sites. The mussels are harvested from a relatively clean area and used as a baseline. Other mussels from this same area are placed in cages at over 90 locations around the sound. They are planted near the zero tide line—average low tide—and left for 60 to 90 days. At that point they are pulled and sent to the Washington Department of Fish and Wildlife where they will be analyzed for a wide spectrum of pollutants, approximately 140 pollutants in total.”

Bivalves are critical to the work these scientists are doing, and to similar water quality research elsewhere.

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Mussel monitoring. (Credit: Puget Soundkeeper.)

“All species of bivalves, including mussels, oysters, and clams, are filter feeders,” the researchers explain. “As they filter water for food, they accumulate many types of contaminants, but do not break them down. Instead, contaminants are stored in the organism’s tissues at levels that reflect the body of water they are in. This makes them ideal for water quality studies.”

Both oysters and mussels are the working bivalves assisting scientists all over the country.

“Despite the name of the program, both mussels and oysters are used for data collection, depending on the location being sampled,” the scientists clarify. “Oysters are used along the mid-Atlantic and southern states through the Gulf, while native mussels are used in the other area. The protocol we use through the Mussel Watch program is part of a national effort by NOAA to use this cost-effective method to get a better picture of what is going on in our waterways with toxic pollution.”

Longer-term plans to install bivalves in the area to help maintain better water quality have been in the works, but have not been without their problems.

“This is where the oysters come in,” explain the researchers. “There are some efforts to use oysters to filter and clean surrounding waters, but this has not been widely done. One effort a few years ago was hampered because the oyster rafts attached to a dock became home for an invasive species of tunicates, and providing a habitat for invasive species is not something we want to encourage!”

However, there are further benefits to using oysters over the long-term if they can make it work within the local ecosystem, as Wilke and Sullivan point out:

“Oysters are also being looked into to see if left-over shells can be used to ease the effects of ocean acidification. Shells left over from harvest can be deployed in areas of low pH to try to reduce the amount of acidification occurring. Easing the effects of ocean acidification will allow existing oyster reefs to have better survival and hopefully increase their range.”

The gains from this research are practical and easily realized.

“What we learn about pollution in Puget Sound through these studies and others will allow us to direct resources for pollution reduction and cleanup to the problem areas and to the chemicals of greatest concern,” state the scientists. “This will help us prioritize actions that will benefit the entire food web including forage fish such as herring, smelt, and sand lance; salmon; orca whales; and even people.”

This research has other, less tangible benefits that the team is excited about, too.

“Not only does this project generate very good data over time, it also does so very cost- effectively because of the volunteer component,” the researchers assert. “And, it generates enthusiasm for citizen science and science in general, which is a good thing. The entire project is overseen by the Washington State Department of Fish and Wildlife, and their lab work follows rigorous protocols from NOAA.”

Expect to keep seeing mighty mussels and oysters working for scientists and improving our water quality all over the country.

Top image: Ribbed mussels held by researcher. (Credit: NOAA)

About Karla Lant

Karla Lant is a professional freelance science writer and a member of the Society of Environmental Journalists. She also covers other scientific and medical stories as well as technology.

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