James J. S. Johnson, JD, ThD, MSGeog, CNHG


Hooked Mussels attached to Oysters, Chesapeake Bay oyster-reef
(Chris Judy / Maryland Dep’t of Natural Resources photo)

And it shall come to pass, that everything that lives, which moves, wherever the rivers shall go, shall live; and there shall be a very great multitude of fish, because these waters shall go there, for they shall be healed; and everything shall live where the river goes.   (Ezekiel 47:9)

Healthy rivers are a good thing. But sometimes a “hero” is needed, to clean up unhealthy rivers, or to “keep clean” rivers that will otherwise go bad.

Tough “clean-up” jobs, as well as “keep-it-clean” maintenance jobs, are often accomplished by unsung heroes. For example, the tough job of cleaning up water quality (and the job of maintaining water quality) in coastal wetlands requires some helpful muscles, such as those of the Chesapeake Bay’s mussels!  So, shouldn’t such helpful bivalves be given due credit, for what they do?

Mussels, once mostly ignored, are now being touted for their ability to clean streams much like oysters do for the Bay. Oysters are in many ways the restoration darlings of the Chesapeake Bay cleanup effort. Touted for multiple benefits — as edible, water-filtering moneymakers — oysters attract both enthusiasm and funding to promote their recovery.

But the popularity of oysters often overshadows the water-cleansing role of other filter feeders such as mussels. A growing group of mussel advocates think it’s high time that the bivalves share the spotlight as clean-water workhorses that can carry the message farther upstream.

 Projects to propagate mussels and restore them to waterways where they once thrived are cropping up in parts of Virginia, Maryland, Delaware and Pennsylvania as researchers working on them in various states begin to join efforts. The goal is to return some of the diversity once found in these waterways — mussel by mussel — so they can filter, feed, clean and otherwise serve the local ecosystem.

[Quoting Whitney Pipkin, “Freshwater bivalves flexing their muscles as water filterers”, CHESAPEAKE BAY JOURNAL, 28(7):1 (October 2018).]

So, what service do mussels provide, such as the mussels which dwell in Chesapeake Bay watershed streams and estuarial wetlands?

Research in Chesapeake Bay shows that the mussels that typically colonize a restored oyster reef can more than double the reef’s overall filtration capacity. Filtering plankton helps improve water quality because these tiny drifting organisms thrive on the excess nitrogen and other nutrients that humans release into the Bay and its tributaries through farming, wastewater outflow, and the burning of fossil fuels. …

Restoring oysters — and their ability to filter large volumes of water — is widely seen as a key way to improve the health of Chesapeake Bay. New research makes this calculus even more appealing, showing that the mussels that typically colonize the nooks and crannies of a restored oyster reef can more than double its overall filtration capacity.

The study — by researchers at the University of Maryland, the Smithsonian Environmental Research Center, and the Virginia Institute of Marine Science — appears as the cover story in the most recent issue of Restoration Ecology [i.e., Keryn B. Gedan, Lisa Kellogg, & Denise L. Breitburg, Accounting for Multiple Foundation Species in Oyster Reef Restoration Benefits, Restoration Ecology, 22(4):517 (May 2014), DOI: 10.1111/rec.12107 ]

“Many efforts to restore coastal habitat focus on planting just one species, such as oysters, mangroves, or seagrass,” says [University of Maryland]’s Keryn Gedan, the study’s lead author. “However, our research shows that the positive effects of diverse ecosystems can be much greater. In the case of oyster reefs, commonly associated species such as mussels may multiply the water quality benefits of restoration by filtering more and different portions of the plankton.”

“Estimates of the ecosystem services provided by a restoration project are used to justify, prioritize, and evaluate such projects,” adds [Virginia Institute of Marine Science] scientist Lisa Kellogg. “By quantifying the significant role that mussels can play in filtration within an oyster-reef habitat, our work shows that the ‘return on investment’ for oyster-reef restoration is potentially much higher than commonly thought.”

Filtering plankton helps improve water quality [and thus functions as an “ecosystem engineer”  —  JJSJ comment] because these tiny drifting organisms thrive on the excess nitrogen and other nutrients that humans release into the Bay and its tributaries through farming, wastewater outflow, and the burning of fossil fuels.

“Filtering plankton from the water is the first step towards removing nutrients,” says Kellogg. “Although some will be returned to the water column, a significant portion will be removed from the system.” Removing plankton also has more direct benefits. Left unchecked, plankton can form dense blooms that shade other aquatic plants such as seagrass, and can lead to low-oxygen “dead zones” when they die, sink, and decay.

The research team, which also included SERC’s Denise Breitburg, based their findings on a combination of laboratory experiments and computer modeling. In the lab, they added phytoplankton of different size classes to tanks containing eastern oysters (Crassostrea virginica) or hooked mussels (Ischadium recurvum), then measured the animals’ filtration rates at different temperatures. They then incorporated these measured rates into a simple model and used that to simulate overall filtration for three different restoration scenarios in Harris Creek, Maryland, one of the East Coast’s largest oyster-reef restoration sites.

Kellogg’s main contribution to the paper was data on the relative abundance of oysters, mussels, and other organisms inhabiting restored oyster reefs collected during her time as a post-doctoral researcher at Maryland’s Horn Point Lab. These data, which showed that the biomass of mussels on a restored reef can equal or exceed that of the oysters, were used as baselines for the model projections.

The results of that modeling were clear. “On average,” says Gedan, “adding filtration by hooked mussels into our model increased the filtration capacity of the reef by more than two-fold.”

Hooked mussels were also twice as effective as oysters at filtering picoplankton,” says Breitburg. Picoplankton are the smallest category of marine plankton, ranging from about 1.5 to 3 microns (a human red blood cell is about 5 microns across). Picoplankton are particularly abundant in Chesapeake Bay during summer, with an earlier study from the York River showing they can make up nearly 15% of phytoplankton “biomass” during the warmer months.

“Some have suggested that oyster reef restoration will be less effective than expected in controlling phytoplankton populations because of oysters’ inability to filter picoplankton,” says Kellogg. “Our discoveries with mussels lessen that concern.”

“The mussels’ ability to filter the picoplankton indicates that they fill a distinct ecological niche,” adds Gedan. “Accounting for both oyster and mussel filtration, large-scale restoration projects like those going on in Chesapeake Bay could significantly control phytoplankton, especially during the summer months, when animals filter the most.”

The bottom line, says Gedan, is that “estimates of the ecosystem services provided by just the oysters on an oyster reef may vastly underrepresent the reefs’ overall contribution. Because oyster reefs also contain many other filter-feeding species, they will likely benefit water quality much more than previous modeling efforts suggest.” Kellogg is now taking this line of research further, studying how another common oyster-reef inhabitant — an organism called a tunicate — might also contribute to gains in water quality. Tunicates, fleshy animals also known as sea squirts, filter plankton and other particles from the water similarly to oysters and mussels.

[Quoting Virginia Institute of Marine Science, “Study Puts Some Mussels into Chesapeake Bay Restoration”, 9-8-AD2014, at ScienceDaily.com posting https://www.sciencedaily.com/releases/2014/09/140908121538.htm .]

Summarized in technical ecology lingo, the researchers abstract their findings on mussel filter-cleaning as follows:

Many coastal habitat restoration projects are focused on restoring the population of a single foundation species to recover an entire ecological community. Estimates of the ecosystem services provided by the restoration project are used to justify, prioritize, and evaluate such projects. However, estimates of ecosystem services provided by a single species may vastly under‐represent true provisioning, as we demonstrate here with an example of oyster reefs, often restored to improve estuarine water quality.

In the brackish Chesapeake Bay, the hooked mussel Ischadium recurvum can have greater abundance and biomass than the focal restoration species, the eastern oyster Crassostrea virginica. We measured the temperature‐dependent phytoplankton clearance rates of both bivalves and their filtration efficiency on three size classes of phytoplankton to parameterize an annual model of oyster reef filtration, with and without hooked mussels, for monitored oyster reefs and restoration scenarios in the eastern Chesapeake Bay.

The inclusion of filtration by hooked mussels increased the filtration capacity of the habitat greater than 2fold. Hooked mussels were also twice as effective as oysters at filtering picoplankton (1.5–3 µm), indicating that they fill a distinct ecological niche by controlling phytoplankton in this size class, which makes up a significant proportion of the phytoplankton load in summer.

When mussel and oyster filtration are accounted for in this, albeit simplistic, model, restoration of oyster reefs in a tributary scale restoration is predicted to control 100% of phytoplankton during the summer months.

[Quoting Keryn B. Gedan, Lisa Kellogg, & Denise L. Breitburg, Accounting for Multiple Foundation Species in Oyster Reef Restoration Benefits, Restoration Ecology, 22(4):517 (May 2014), DOI: 10.1111/rec.12107 ]

Wow! Good for the Eastern Oysters, for their work in filter-cleaning Chesapeake Bay estuarial picoplankton, yet compliments also to the Hooked Mussels for their respective contributions to the clean-up work!  (This illustrates good teamwork!)

But it’s not just the brackish waters of Chesapeake Bay wetlands that host mussels. (Thus, there are other waters that benefit from mussel cleaning.)  In fact, mussels often thrive in riverine freshwater habitats other than those which limnologists would classify as “coastal wetlands”.


Texas Freshwater Mussel life cycle   (Texas Parks & Wildlife Dep’t image)

In Texas, for example, freshwater mussels are both plentiful and diverse, living in both lotic (running) and lentic (standing) bodies of water.

Freshwater mussels may inhabit a variety of water-body types including large and small rivers and streams, lakes, ponds, canals, and reservoirs. More stable habitats may have larger and more diverse populations than do smaller and less stable waters.  Some species tolerate a wide variety of conditions [e.g., various bottom types, currents, water depths, water pH and other chemistry factors, water clarity, amount of sunlight, turbidity, aquatic vegetation, percentage of dissolved oxygen saturation, water temperature, biotic community make-up, etc.], but others may be more specific.  Certain mussels may require moderate to swiftly flowing waters, and typically fail to survive in lakes or impoundments.

Headwater spring pools and streams in Texas Hill Country typically harbor few if any mussels largely because the cool, clear waters lack sufficient phytoplankton and other foods needed to support mussel populations. A few species like pondhorns (Uniomerus spp.) occur in temporary ponds and periodically-dry portions of intermittent streams by burrowing into the substrate during dewatering.

[Quoting Robert G. Howells, Raymond W. Neck, & Harold D. Murray, FRESHWATER MUSSELS OF TEXAS (Texas Parks & Wildlife Department, Inland Fisheries Division, 1996), page 14.]

In Texas, for instance, freshwater mussels —  especially dozens of varieties of unionid mussels (freshwater-dwelling mollusk bivalves a/k/a “naiads”)  —  have flourished for centuries in the enormously biodiverse bayou-waters of Caddo Lake, Texas’ sole “natural lake” (which borders Louisiana).

However, freshwater mussels have also been studied in these major river systems of the Lone Star State:

Canadian River (only slim pickings in these Panhandle-traversing waters); Red River (serving as the Texas-Oklahoma border to Arkansas, swelling at the artificially expanded Lake Texoma, favoring mussel populations including unionids such as pondshell, pondhorn, and yellow sandshell, as well as some clams);

Sulphur River (a Red River tributary, once intensively fished for mussels);

Big Cypress Bayou (a tributary of Caddo Lake, once fished for mussel pearls);

Sabine River (flowing to Texas’ border with Louisiana, then into the Gulf of Mexico, once intensively fished for mussels);

Neches River, including its tributary Angelina River (flowing through Texas piney woodlands, with no recent major harvesting of mussels);

Trinity River, flowing into Trinity Bay (pollution has been a historic problem, killing off mussel populations, though some unionids are observed within Lake Lewisville, an artificially formed reservoir-tributary of the Trinity River drainage system);

San Jacinto River (flowing north of Houston, draining into Trinity Bay, hosting washboard and threeridge mussels – as evidence by mussels stranded in dewatered areas during droughts);

Brazos River (Texas’ longest river between the Red River and the Rio Grande, hosting unionids in its tributary Navasota River);

Colorado River (containing unionid mussels in several of its tributaries);

Lavaca River (no significant mussels observed);

Guadalupe River, with its primary tributary San Antonio River, plus other tributaries including Blanco River and San Marcos River (sporadically hosting washboards and other river mussels);

Nueces River (flowing into Nueces Bay, with muddier tributaries hosting some mussels); and the Rio Grande, including its tributary Pecos River (separating Texas from Mexico, and variously hosting some unionid mussels).

[For specific biogeography details, see Howells, Neck, & Murray, FRESHWATER MUSSELS OF TEXAS, pages 29-32.]

The water-filtering benefits of wetland mussels are worthy of appreciation; however, not every impact of mussels is advantageous, as is illustrated by the invasive (and pervasive) nuisance known as the non-unionid Zebra Mussel (Dreissena polymorpha).  The miniscule Zebra Mussel is not covered as a topic, here, except to notice that it has caused a lot of disturbing and non-miniscule impacts in many freshwater lakes of America and Europe, from one water-body to another, due to over-land transport as attachments to the hulls of recreational boats.  [Regarding Zebra Mussel nuisance impacts, see Winfried Lampert & Ulrich Sommer, LIMNOECOLOGY: THE ECOLOGY OF LAKES AND STREAMS, 2nd ed. (Oxford University Press, 2010), pages 123 & 224-225.]

Freshwater mussels come in all shapes and sizes, with nicknames that indicate their unique forms or textures, such as snuffbox, spectacle-case, pimple-back and pistol-grip. Most live in rivers or streams, some others in lakes and ponds, but all rely on a current of water to provide phytoplankton and bacteria that they filter-feed from the water. Some species can live to be more than 100 years old. They also have a complex life cycle that makes them difficult — but not impossible — to reproduce in hatcheries. Most need a fish to act as a host as they start their life: The larvae find shelter and grow in fish gills until they can navigate the waters on their own. Some mussels create lures to draw in their preferred host, and some clamp onto the fish with trap-like mouths. If the fish species preferred by a certain mussel disappears, the mussel does, too.

[Quoting Whitney Pipkin, “Freshwater bivalves flexing their muscles as water filterers”, CHESAPEAKE BAY JOURNAL, 28(7):1,17 (October 2018).]

In order to analyze the benefits of coastal wetland mussels, such as those which are quietly filter-cleaning wetland waters within the Chesapeake Bay drainage watershed, someone needs to carefully study them.

But, since most of these mollusks are not commercially exploited, who will pay for the scientific research on these humble bivalves?

Other parts of the country, such as the Tennessee River system and Delaware Bay, have seen the fruit that comes from investing in mussel propagation and research. Meanwhile, mussels have often fallen below the radar of Chesapeake Bay restoration efforts. That may be because freshwater mussels, unlike oysters or some saltwater mussels, don’t end up on human plates.

Research and restoration funding is harder to come by, even though three-quarters of freshwater mussel species are considered to be at some level of impairment. The money often comes in an off-and-on fashion from mitigation payments for environmental disasters and permit renewals, and partners in the Chesapeake Bay restoration effort community have not focused their resources on mussels. … Many of the mussel advocates who gathered along the James River in July first interacted with the mollusks outside of the Chesapeake Bay watershed — in the Clinch River, which rises in the southwest corner of Virginia and flows into Tennessee. The Clinch River is home to most of Virginia’s 81 mussel species, more than a third of which are endangered. The diversity of mussels found there has made the river a hotspot for research nationally. …

The Harrison Lake facility [i.e., the Harrison Lake National Fish Hatchery, located along the James River south of Richmond, Virginia – an activity of the U.S. Fish & Wildlife Service, U.S. Department of the Interior], built in the 1930s to support recreational fisheries, now has the capacity to grow tens of millions of mussels. Over the last decade, the facility transitioned from a focus on migratory fish species such as American shad to also growing tiny glochidia, the name for larval-stage mussels, into young mollusks.

When Dominion’s Bremo Power Station renewed its water discharge permit, the hatchery got more than a half-million dollars from the deal after a threatened mussel was found to be impacted by its discharge. When DuPont had to pay $42 million to settle a case over mercury contamination of the South River, the hatchery got $4 million. The coal ash spill in the Dan River in 2014 brought in additional funds to help replenish mussel species that might have been lost.

[Quoting Whitney Pipkin, “Freshwater bivalves flexing their muscles as water filterers”, CHESAPEAKE BAY JOURNAL, 28(7):1,17 (October 2018).]

HarrisonLake-hatchery-sign.USFWSThe Harrison Lake National Fish Hatchery employs a staff of five – and their aquaculture efforts are producing results.

The hatchery team used to release tiny mussels into portions of the James watershed and hope for the best. Now, the staff has the technology to grow them “almost indefinitely” at the facility to a large enough size that they have much better survival rates in the wild. The center propagates the mussels by collecting female mussels that already have larvae in their gills, which the staff either extracts with a needle (to mimic a fish rubbing against it) or allows the mussel to release. Placed into tanks with their host fish, the larvae will attach to the fish before dropping off two to four weeks later to continue feeding and growing in a series of tanks. The lab is also working on in vitro fertilization for mussel species whose host fish is not known.

[Quoting Whitney Pipkin, “Freshwater bivalves flexing their muscles as water filterers”, CHESAPEAKE BAY JOURNAL, 28(7):1,17 (October 2018).]

In order to track progress, regarding the future growth and activities of mussels released to “the wild”, the hatchery uses a monitoring system that is analogous to bird-banding  —  the hatchery laser-etches identifying code markings onto the shell of a mussel, before release.  Also, some rare mussels receive special tagging.

At the hatchery, in a squat building paid for by the Bremo mitigation funds, biological science technician Bryce Maynard demonstrated methods used to tag and track the progress of mussels grown here before being launched into wild waters. He flipped the switch on a laser engraver that can carve numbers into several rows of mussels at a time, leaving a burnt-hair smell in the air and marking thousands of mussels a day for future tracking. Among the hatchery mussels are rare species such as the James spinymussel, which was once abundant in the James River upstream of Richmond but disappeared from most of its range by the late 1980s. The hatchery-raised spinymussels are marked with tags sealed in place with dental cement. The tags can be located later with a beeping detector but are costlier than other tracking methods.

[Quoting Whitney Pipkin, “Freshwater bivalves flexing their muscles as water filterers”, CHESAPEAKE BAY JOURNAL, 28(7):1,17 (October 2018).]

So what is the main benefit expected from these costly investment? Besides overall enhancing of the coastal wetland ecosystems, water filtering is expected, since that is what mussels are famous for.

Every mussel that finds its way into the watershed and survives could help filter about 10 liters of water per day, said Danielle Kreeger, senior science director at the Partnership for the Delaware Estuary, where she’s become an advocate for the potential of what she calls the #mightymussel.  “Pound for pound, freshwater mussels are not slouches,” she said  …  “To me, every mussel is precious, and we need to protect them.”  Kreeger, in the coming months, will be completing a review of studies on the ability of such bivalves to enhance water quality, which she hopes will shore up the amount of data available about mussels’ benefits.

[Quoting Whitney Pipkin, “Freshwater bivalves flexing their muscles as water filterers”, CHESAPEAKE BAY JOURNAL, 28(7):1,17 (October 2018).]

To be clear, the Harrison Lake National Fish Hatchery is not limited to hatching mussels for the Chesapeake Bay’s tributary waters.

In fact, the USF&W operation there is, as one would expect, focused largely on piscatorial aquaculture, i.e., hatching fish, especially American Shad, as well as some alewife, blueback herring, hickory shad, and striped bass. [See “Harrison Lake national Fish Hatchery”, https://www.fws.gov/harrisonlake/ summary by the U.S. Fish & Wildlife Service.]

But for now, the take-away lesson is an appreciation for mussels: they are a lot more important than most of us think they are.


Harrison Lake Nat’l Fish Hatchery: fish hosts carrying mussel larvae    (B. Davis / USF&WS photo)

But why are they, as Dr. Kreeger says, “precious”? Because God created them  —  it was God Who gave Chesapeake Bay mussels, as well as Texas riverine mussels, their intrinsic value.  As God’s creatures they display His workmanship – God’s creative bioengineering is exhibited (“plainly seen”) in all animals, including humble mussels.

Accordingly, as some of the many (albeit small and usually unseen) creatures whom God chose to create (and to “fill” diverse wetland habitats), mussels deserve due credit, for doing what God has programmed them to do, including filter-cleaning wetland waters.

So, good for the mussels, good for the water supply, and that’s all good for us —  and therefore we should give glory unto God, because God is due credit for making estuarial and river-dwelling mussels what they are.                               ><> JJSJ  profjjsj@aol.com

Dr. James J. S. Johnson freely admits that his appreciation for mussels did not begin with learning about how they contribute to filter-cleaning estuarial waters, but rather from his eating lots of tasty blue mussels when visiting New England.