This species is not rare, and not considered in need of special conservation effort.
US Federal List: no special status
CITES: no special status
State of Michigan List: no special status
The primary defense of ribbed mussels is their shell. In their native range, their main predator is the blue crab (Callinectes sapidus). The mud crab Panopeus herbstii is also known to feed on them. Higher survivorship in mussels high in the intertidal zone suggest that marine predators are more important than terrestrial ones.
Shore birds, including clapper rails (Rallus longirostris), willets, and dunlins have been recorded feeding on them in San Francisco Bay (Cohen, 2005). One study found ribbed mussels to be more than half the prey (by volume) in stomachs of California clapper rails (Rallus longirostris obsoletus).
Some rails have been found to have ribbed mussels clamped to their toes, and others are found missing toes.
Known Predators:
Ribbed mussel are relatively large mussels. They range from 5 - 10 cm (4 inches) in length. The largest specimen recorded reached 13 cm. The shell is moderately thin and oblong or fan shaped. The upper margin is straight or slightly convex. The dorsal and ventral margins are parallel.
The periostracum (thin, glossy outer shell layer) is glossy, brownish black with some yellow to a bleached white color. It is grooved with pronounced, unbranched, radiating ribs, largest on the upper part of the hind end above a broad umbonal ridge, fine along lower margin. These give the species its common name. The inside of the shell is pearlescent, sometimes white or bluish-gray, tinged with purple/blue or purple/red at hind margin. There are no teeth at the hinge. At the head end of the shell there is no shelf on the inside.
In the summer, the color of the mantle varies between the sexes. In females the mantle tends to be a medium chocolate brown, in males is is lighter, a yellowish cream white color.
The broad umbo (hump at the center of the concentric growth lines) is a short distance behind the narrowed, rounded front end. The periostracum is often worn away around the umbo. There is no external siphon.
Like most bivalves, the species has a muscular "foot", capable of moving he animal slowly through sediment, . The foot can also secrete byssal threads -- hair-like adhesive filaments that help the mussel attach to grasses, nearby shells, or other solid objects.
One subspecies of Geukensia demissa is recognized. G. d. granosissima (Sowerby, 1914) ranges from the east and west coast of Florida to the Gulf of Mexico (Yucatan). It differs in the morphology of the shell (rib number) and ultrastructure.
Range length: 13 (high) cm.
Other Physical Features: ectothermic ; heterothermic ; bilateral symmetry
Sexual Dimorphism: sexes colored or patterned differently
The age of ribbed mussels can be determined by back counting the annual growth ribs on the shell.
Mortality of plankton larvae is unknown. Mortality rates of juveniles in the year following settlement have been recorded to average about 55 % partially due to winter icing on the marsh.
Even though mussels are less abundant higher on shore, survivorship increases with increasing tidal height. Some reach 15 years or older. Mussels on the marsh edge tend to be around 6 or 7 years old.
Average lifespan
Status: wild: 15 years.
The larvae of ribbed mussels settle on subtidal oyster reefs, in intertidal salt marshes and on man-made structures in these habitats. Sometimes they attach to one another in aggregations or to clumps of hollow grass stems (Spartina alterniflora) in low marshes. They are most abundant at the lowest shore levels within salt marshes and occur in small numbers in the high marsh zone above the average high water mark.
These mussels can tolerate water temperatures up to 133 degrees F (56°C) and and wide range of salinities, from near fresh water up to 70 ppt (twice the concentration of seawater).
Habitat Regions: saltwater or marine
Aquatic Biomes: benthic ; reef ; coastal ; brackish water
Wetlands: marsh
Other Habitat Features: estuarine ; intertidal or littoral
The ribbed mussel is native to the Atlantic coast of North America, from the southern Gulf of St. Lawrence, Canada to northeastern Florida and along the Gulf of Mexico from Florida to Yucatan.
In the mid 1800s the ribbed mussel was introduced to San Francisco Bay, California, apparently by accident, included with live oysters shipped by trans-continental rail for cultivation in the Bay. Since then it has been found in other locations on the Pacific coast, from Alamitos Bay south to Anaheim Bay, Newport Bay, Bolsa Chica Lagoon and Estero de Punta Banda, Baja California Norte, Mexico. The locations may have been sites of unrecorded oyster transplants, or the mussels may have arrived after attaching to hulls or other mobile objects.
Biogeographic Regions: atlantic ocean (Native ); pacific ocean (Introduced )
When covered with water, the mussels opens and cilia on its gills draw water and food in. The ribbed mussel's primary diet consists of microscopic plankton and particles of detritus.
Animal Foods: zooplankton
Plant Foods: phytoplankton
Other Foods: detritus ; microbes
Foraging Behavior: filter-feeding
Primary Diet: planktivore ; detritivore
Mussels are important in changing nutrient dynamics of marsh and estuary. They help cycle energy, phosphorous and nitrogen.
The ribbed mussel has a mutualistic relationship with marsh grass, Spartina alterniflora. Mussels attach to the base of the stem with their byssal threads. As a byproduct of their filter-feeding, they deposit fecal material on the surrounding sediment. This stimulates the grass to grow by increasing the soil nitrogen. Overall they increase marsh net primary production and stability.
Geukensia demissa is a host for the flatworm, Paravortex gemellipara.
Mutualist Species:
Commensal/Parasitic Species:
These mussels help maintain saltmarshes, which are important nurseries for food fish and shellfish. Ribbed mussels can also be very useful bioindicators for pollution assessment studies.
The mussel is also an important prey species for desirable shellfish and bird species.
Ribbed mussels are edible, but are generally not considered to taste good. They can accumulate toxins from their environment, especially while exposed at low tide, and so should not be harvested then.
Positive Impacts: research and education
There should be no low tide collection of mussels. Mussels retain the pollution inside when their shells are closed. This can cause humans to become sick if eaten.
The high abundance and biomass of Geukensia demissa in Pacific coast wetlands (where it is not native) is a concern for conservation of these threatened habitats.
This species has a planktonic larval stage that allows for dispersal to distant locations. The larvae settle out of the water column and attach to oyster reefs, saltmarsh plants, and other solid objects in shallow or intertidal waters. They then transform into the sedentary shelled form. Subsequent growth rate and time to maturity is strongly determined by environmental conditions, including tidal exposure, temperature, and available food. Time to ma
Development - Life Cycle: metamorphosis
Communication Channels: tactile ; chemical
Perception Channels: visual ; tactile ; chemical
Ribbed mussels are broadcast spawners. At a particular time of year, individuals release eggs and sperm into the water, and fertilization occurs there.
Mating System: polygynandrous (promiscuous)
Sexual maturation in this species is primarily determined by body weight, and this in turn is strongly influenced by the environment of individual mussels. Along the edge of the marsh, mussels usually become sexually mature during their second growing season. The minimum size for gametogenesis is around 12 mm. The average size for the sexually mature ribbed mussel is greater than 20 mm. A few meters from the edge of the marsh, the minimum size increases to about 17 mm. Higher up on shore, it is not uncommon to see mussels greater than 35 mm that do not show any external characteristics of gametogenesis. Mussels that are farther from the marsh edge tend to grow slower as a result of shorter submergence and feeding time, which can delay maturation an additional year compared to the mussels along the edge of the marsh.
The ribbed mussel spawns by external fertilization, sperm and eggs are released into the water column.
Gametogenesis begins in early spring and peaks in June and July. Maximum reproduction occurs between June and August, depending on location, and larvae can be found into early fall.
Breeding interval: It is unknown how many times they spawn during one summer, but it is thought to be only one time.
Breeding season: in the summer months
Key Reproductive Features: iteroparous ; seasonal breeding ; gonochoric/gonochoristic/dioecious (sexes separate); sexual ; fertilization (External ); broadcast (group) spawning
There is practically no parental investment in this species -- eggs do not receive substantial provisioning, and there is no interaction with offspring after gametes are released.
Parental Investment: no parental involvement
Geukensia demissa is a species of mussel, a marine bivalve mollusk in the family Mytilidae, the true mussels. This species is native to the Atlantic coast of North America. The common names for this species include ribbed mussel, Atlantic ribbed marsh mussel and ribbed horsemussel.[1] However, the common name ribbed mussel is also used for the Southern Hemisphere mussel Aulacomya atra. The appearance of the shell is grooved and oval in shape. The interior of this mussel is tinted purple
The ribbed shells of this species usually attain a length of 10 cm length, and can be as large as 13 cm.[1] Age can be determined by counting dark growth rings on the shell and mussels typically live 10 – 15 years, but more advanced ages are not uncommon.[2]
The ribbed mussel occurs in the coastal waters of salt marsh habitats from the southern Gulf of St. Lawrence in eastern Canada, south along the western Atlantic coast to Florida. In the Gulf of Mexico this species is replaced by the southern ribbed mussel, Geukensia granosissima, and the two species hybridize in southern Florida.[3]
The ribbed mussel has been introduced to Texas, Mexico, California, and Venezuela.[1]
Ribbed mussels live in the intertidal zone, attached to hard surfaces or embedded in sediment with the help of their byssal threads. They are typically found in salt marshes where they form dense aggregations with the marsh cordgrass (Spartina alterniflora) and each other since aggregating near one another decreases an individual's chance of being preyed on.[4]
Ribbed mussels are highly effected by small variations in temperature which makes their placement in the marsh important due to how variable temperature can be in salt marshes. Mussels that are in dense Spartina patches tended to be warmer than those who were not, and the amount of air flow that mussels receive can make a difference as well. Their position in the depth of the sediment also effects their internal body temperature.[5]
Another example of how important microhabitats are for ribbed mussels is tidal height. In higher tidal zones, ribbed mussels do not grow to full potential and there are few out there; however, they tend to be live long and have a better chance of survival.[4]
Ribbed mussels face more predation on marsh edges as well. Some of their predators include birds, raccoons, and blue crabs.[6]
Ribbed mussels are dioecious and sexes can only be determined histologically.[7]
They reproduce once per year in Connecticut[7] and South Carolina,[8] however in an introduced population in Venezuela two spawning peaks have been observed.[9]
Mussels>15 mm are typically reproductive; however, it is not uncommon for mussels up to 35 mm to have no signs of gametogenesis. Their location in the salt marsh plays a role in when they become reproductive because edge ribbed mussels mature at smaller body sizes compared to other mussels.[10]
Ribbed mussel larvae return to the marsh during recruitment, and they tend to settle near marsh edges where there are adult ribbed mussels.[11]
The ribbed mussel is primarily a filter feeder, and they help to clean said area of bacteria, parasites, and heavy metals.[12] They feed on phytoplankton, bacteria, and non flagellates to gain nutrients.[13]
The speed at which ribbed mussels feed changes with temperature which is partially due to the availability of their food, and they feed more when their environment is warmer. Location also plays a role in filtration rates due to food quality and availability.[14]
Ribbed mussels and other shellfish are able to store nutrients in the bodies and shells, through a process that may also remove toxins from the environment,[15] and they can be used as bioindicators for certain pollutants like coliform bacteria.[16] Ribbed mussels have been found with heavy metals in their tissues which suggests that they can filter such toxins out of the ecosystem. They also feed on algae, so they could be used to prevent harmful algal blooms.[15]
Spartina grasses benefit from the presence of mussels because ribbed mussels increase nutrients in sediment that Spartina need to grow. For example, mussels contribute bioavailable nitrogen in their pseudofeces. When ribbed mussels form mussel mounds, they are able to stabilize the ground to make it easier for Spartina to grow on.[17]
Native Americans near the Jamestown settlement manufactured shell beads that were called "rawrenock" in the local Powhatan language. The production process involved grinding broken ribbed mussel shells into disk-shaped beads and drilling a central hole to string the jewelry with. Surviving examples were recovered from the refuse that filled an abandoned well within the James Fort.[18]
Geukensia demissa is a species of mussel, a marine bivalve mollusk in the family Mytilidae, the true mussels. This species is native to the Atlantic coast of North America. The common names for this species include ribbed mussel, Atlantic ribbed marsh mussel and ribbed horsemussel. However, the common name ribbed mussel is also used for the Southern Hemisphere mussel Aulacomya atra. The appearance of the shell is grooved and oval in shape. The interior of this mussel is tinted purple
The ribbed shells of this species usually attain a length of 10 cm length, and can be as large as 13 cm. Age can be determined by counting dark growth rings on the shell and mussels typically live 10 – 15 years, but more advanced ages are not uncommon.
