We Need More Ribbed Mussels For Urban Water Restoration
By Joe Reynolds, Exc Director Save Coastal Wildlife
How many mussels can you name? No, I don’t mean the muscles in your body, which are organs that help to create a particular movement.
For this article I am referring to mussels that you may find in the water. It’s a type of shellfish.
The world is full of mussels. They can be found living and breathing in fresh water lakes, streams, creeks, and estuaries and along an ocean coastline. In fact, different species of mussels can be found existing in nearly all of the world’s waters, even in extreme places: deep-sea depths near hydrothermal vents and in the planet’s polar seas in the Antarctic and Arctic Oceans.
Similar to a clam, another type of mollusk, mussels live in a shell, but their shell is more oblong than oval and darker in color with hues of green, purple, blue or brown. Mussels also tend to exist with other mussels of the same species in thick clusters anchored or sticking together to hard structures, such as shells, pilings, or rocks, with very strong, silky protein fibers, called byssus threads. These slim but sturdy threads help mussels stay put and can be difficult to dislodge.
Some of the mussels I am most familiar with include the zebra mussel (Dreissena ploymorpha), which is a freshwater mollusk native to Poland and the Soviet Union, but which has become an invasive species and a hated pest along the Hudson River in New York State. A freshwater mussel whose population is more loved, but sadly in decline is the rabbitsfoots (Quadrula cylindrical). It gets its name from a shell that, of course, is shaped like a rabbit's foot. It’s a federally threatened species that has been lost from about 64 percent of its historical range from polluted streams of the Verdigris River, a tributary of the Arkansas River in southeastern Kansas and northeastern Oklahoma.
Closer to my home along the Jersey Shore there are blue mussels (Mytilus edulis), which are actually global species found in temperate and polar waters. Blue mussels may be known by other names depending on where you go, such as bay mussels, farmed mussels and Prince Edward Island (PEI) mussels. This bivalve is a favorite dish among many shellfish lovers, including me, and is cultivated and caught in the wild to serve as a delicious meal.
But not all mussels are edible or easily understood. Take another mussel close to my home - the Atlantic ribbed mussel (Geukensia demissa). These little sea creatures are not well known by most people, and they don’t look like much at first glance. Their shell is shaped like a long rounded triangle with dark grooved ribs similar to corduroy pants.
Although ribbed mussels are edible, you have to be really hungry to eat one. The meat is rubbery and tough to chew. The meat can also be loaded with organic bacteria, which gives it a slightly metallic taste. Thus, unlike the blue mussel, people do not commonly eat ribbed mussels.
Yet, the qualities that make ribbed mussels so difficult to eat are the perfect indigents to improve water quality and keep wetlands happy and healthy.
Clumps of Atlantic ribbed mussels thrive in estuarine and tidal wetland waters living largely in the mud and muck among the roots of Spartinagrasses, including smooth cordgrass. Adult ribbed mussels partially bury themselves in the mire, wedged within stems and roots with the aid of a dense protein byssus. By existing so tightly packed together with plant roots, ribbed mussels help to stem erosion in wetlands by wind and water and contribute to salt marsh resilience by helping to trap wetland sediments to buildup a marshy coastline.
While ribbed mussels do not build reefs, nor are they keystone species like an oyster, they are native to the East Coast and are extremely hardy estuarine creatures. The mussel is eurythermal, which means they can survive in extreme water temperatures from -7.6 to 104 degrees F. They can also survive in salinities from 5 to 100 parts per thousand. Ribbed mussels are moreover photosensitive and can respond to the shadows of predators, like raccoons and blue crabs, by closing its shell when submerged during high tide or exposed during low tide.
Yet, what makes ribbed mussels really extraordinary to me is that they are filter feeders. They literally find food by opening up their mouth and taking in whatever minute organisms happen to be swimming in the water at that time, and then filtering out all the unfavorable stuff.
During high tide, ribbed mussels open their shells slightly to draw in water, filtering out algae and other particles. Ribbed mussels can filter 6.8 liters of estuarine water an hour. Take this one step further, a sizeable cluster of ribbed mussels can filter and help remove bacteria, microalgae, nutrients and contaminants of all the water entering a marsh during each high tide cycle. That is truly incredible.
The water filtered by these animals is effectively being cleaned because particles are being removed. The water is cleaner and allows other life to thrive within the estuary.
Since ribbed mussels are not sold to fish markets or restaurants, there is also little fear that whatever the mussels eat will make people sick. Ribbed mussels are amazing natural tools to improve water quality.
There is also science to back up this claim. A November 21, 2017 paper issued by NOAA Fisheries Service details a scientific study where researchers at NOAA Fisheries Milford Laboratory in Milford, Connecticut began a two-year pilot project in June 2011 using ribbed mussels “in an industrial area near Hunt’s Point in the South Bronx, not far from a sewage treatment plant. The waters were closed to shellfish harvesting because of bacterial contamination.” Scientists then monitored the condition of the ribbed mussels and water quality over time to see how each responded.
What the scientists found at the conclusion of the study was that the mussels were largely healthy and still living, and that they removed an estimated 138 pounds of nitrogen from the Bronx River. The researchers estimated “that a fully populated 20 x 20 foot mussel raft similar to the one used in this study would clean an average of three million gallons of water and remove about 350 pounds of particulate matter, like dust and soot, daily. When harvested, the animals could be used for fertilizer or as feed for some animals, recycling nutrients back into the land.”
The researchers with NOAA Fishers Service concluded that the Bronx River study was the first to “examine the use of ribbed mussels for nutrient bioextraction in a highly urbanized estuarine environment….the study also supports the use of ribbed mussels as a management tool for nutrient bioextraction in a range of coastal environments.” Perhaps even the Jersey Shore.
Many people know that salt marshes provide a variety of ecosystem services that include acting as the estuary’s kidneys by filtering water, retaining floodwaters and buffering against powerful storm surges, and providing important spawning sites, foraging areas, and nesting grounds for many species of fish, birds, and invertebrates. Unfortunately, tidal wetlands have declined globally and along the Jersey Shore; and are increasingly threatened by erosion, sea level rise, and ever encroaching urban development.
Restoring sizeable healthy populations of ribbed mussels (and other bivalve shellfish such as oysters) will make sure there is an added natural infrastructure capable within tidal wetlands to remove or transfer large amounts of nitrogen, and microorganisms; and help to contribute to salt marsh resilience.
Taken all together, ribbed mussels and other filter-feeding animals are important tools in restoring tidal wetlands and water quality. In addition, people do not commonly eat ribbed mussels; they do not pose a human health threat and thus make ribbed mussels a perfectly safe ingredient in improving local quality for all species to enjoy.