The Amazing Mussel Reveals Its Secrets
WHAT produces a waterproof superglue, acts like a vacuum cleaner, and even teaches scientists about gene repair? The humble little shellfish known as the mussel!
Mussels are found worldwide. Some live in the sea. Others inhabit freshwater streams and lakes. Inside their double-valved shell lies a soft body that is covered with a skinlike organ called a mantle. As is the case with all mollusks, the mantle forms the shell by mixing calcium and carbon dioxide, which are extracted from the creature’s food and the surrounding water. To match that ability, we humans would have to eat rock fragments, process them inside us, and then release them as prefabricated building materials that automatically make walls and roofs! But it is not the shell that is exciting researchers; it is the marine mussel’s foot.
Try to pry a mussel from a rock, and you will discover what an incredibly firm grip it has—a necessity if the mussel is to resist the sharp beak of a hungry seabird or the pounding waves of the sea. How does it manage to cling so tight? When it chooses a place to set up home, it pokes its tongue-shaped foot out of its shell and presses it against a solid surface. Special glands secrete a fluid mixture of proteins into a groove that runs the length of the foot. This liquid quickly hardens into a fine, elastic thread about an inch [2 cm] long. Then a tiny padlike structure at the end of this thread squirts out a dab of natural adhesive, the mussel lifts its foot, and anchor line number one is complete. These strategically placed threads form a bundle called the byssus, which tethers the mussel to its new home in much the same way that guy ropes hold down a tent. The whole procedure takes only three or four minutes.—See diagram.
Imagine having a very strong glue that is non-toxic and so flexible that it can penetrate the tiniest nooks and crannies, sticking to any surface, even under water. Shipbuilders would welcome it for repairing vessels without the expense of dry-docking them. Autobody workers would like a really waterproof paint that keeps the rust out. Surgeons would value a safe adhesive to join broken bones and to close wounds. Dentists could fill cavities and mend chipped teeth with it. The list of possible uses appears endless.
However, scientists are not thinking of using the mussels themselves to produce this superglue. It would take some 10,000 shellfish to make just one gram of glue. So collecting enough mussels to supply the world’s demand for superglue would wipe out the mussel population, many species of which are already endangered. Instead, American researchers have isolated and cloned the genes for five mussel adhesive proteins, and they are about to mass-produce them in the laboratory so that industries can test them. British scientists too are conducting research on one of these adhesive proteins. However, the mussel is still one jump ahead. Only the mussel instinctively knows the exact blend of proteins needed for each kind of surface. Molecular biologist Frank Roberto has asked admiringly: “How are you ever going to mimic that?”
The Vacuum Cleaner
Mussels are filter-feeders. In most species each mussel daily draws several liters of water into its body and strains out not only food and oxygen but also pollutants like harmful bacteria and toxic chemicals. This ability makes mussels splendid water purifiers. It also makes them handy early-warning detectors for water contamination. For example, hundreds of mussels have been put into the sea around the Ekofisk oil field off the coast of Norway. Every few months scientists pry them up and measure the amount of pollution in their shells to see if chemicals discharged into the sea are harming marine life. Since 1986, mussels and oysters have been put to work in the Mussel Watch Project operating in coastal and inland waters around North America. Researchers get a good idea of any changes in water quality by annually checking the shellfish for buildup of chemicals inside them. How useful!
One freshwater species, the striped zebra mussel, is often regarded as a pest. This thumbnail-size native of eastern Europe was likely introduced into North America by accident in the mid-1980’s when a transatlantic ship discharged its ballast water. Far from its natural enemies, the zebra mussel has multiplied rapidly in the Great Lakes and adjoining waterways, causing millions of dollars’ worth of damage by clogging up water-intake pipes and encrusting boats, piers, and bridges. It has also crowded out some native mussel species.
There is, however, a plus side. Because zebra mussels are filter-feeders par excellence, they quickly clear murky lake waters by gobbling up the floating algae. Underwater green plants can then flourish again and provide a home for other lake inhabitants. Scientists are currently exploring the idea of using the mussels’ filtering prowess to strain out harmful bacteria from public water sources and even to remove sewage from wastewater treatment plants.
Did you know that certain freshwater mussels produce natural pearls, some of them quite valuable? If you have ever worn jewelry inlaid with mother-of-pearl or used pearl buttons, these too might well have been made from mussels. Shiny rainbow-colored mother-of-pearl, also called nacre, comes from the inner layer of their shells, and it is often used in the cultured pearl industry. A very small mother-of-pearl bead, cut from mussel shell, is inserted into an oyster. Thus stimulated, the oyster begins coating the irritation with layers of nacre, eventually producing a pearl.
Of course, some sea mussels also feed us! For centuries people have enjoyed eating the mussels’ delicate, nutritious meat in a variety of ways. In French homes you might sample moules marinière, that is, mussels steamed in a stock of white wine and shallots. The Spanish prefer them in the colorful dish paella, while the Belgians serve them in a large, steaming pot accompanied by French fries. Harvesting mussels commercially is big business around the world, although in some European countries family-run enterprises still operate. A word of warning: If you plan to sample this tasty food, make sure that your shellfish come from a reliable source, and never collect your own supply from the beach unless you are absolutely certain the water is unpolluted.
Who knows what other secrets the mussel will reveal? After all, some of these creatures are thought to live longer than a century! The mussel has a tiny heart that pumps clear blood, but it does not have a brain. So how does the mussel do the amazing things described above? The Bible answers: “Show your concern to the earth, and it will instruct you; and the fishes of the sea will declare it to you. Who among all these does not well know that the hand of Jehovah itself has done this?”—Job 12:8, 9.
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The Gene Repairer
The deep-sea mussel lives in one of the most hostile places on earth, the Mid-Atlantic Ridge, where hot-spring vents spew out highly toxic chemicals that continuously damage the creature’s genetic makeup. Yet, special enzymes enable this mussel to keep mending its DNA. Scientists are studying these enzymes in hopes of discovering how to repair human DNA damaged by disease or aging.
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The Anchoring Method Used by Many Mussels
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Mussels are splendid water purifiers
Ontario Ministry of Natural Resources/Michigan Sea Grant
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Asian green mussel
Villosa iris mussel
(Mussels not shown to scale)
Asian green: Courtesy of Mote Marine Laboratory; zebra: S. van Mechelen/University of Amsterdam/Michigan Sea Grant; villosa iris mussel and bottom left: © M. C. Barnhart
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Paella, a colorful Spanish dish, often includes mussels