General Topics

Freshwater Mussels of Missouri

Mussels in Missouri

Mussels, members of the Bivalvia class, are important to the health of Missouri’s river ecosystems (McMurray et al. 2012). Mussels improve the quality of the water by filtering bacteria, algae, and more, which helps cycle nutrients throughout the water. They also are a food source for fish, some small mammals, and birds. Their presence is a good indicator of water quality and the overall health of the ecosystem. The shells left behind when mussels die have been used for buttons, and some mussels can be used for the production of pearls.

At the end of this web page is the Guide to Missouri Mussels Spreadsheet that can be downloaded and sorted to obtain information on certain types of mussels and to help with identification of mussels based on their characteristics.

Mussels Throughout History

Native Americans used mussels for meat, tools, and jewelry (McMurray et al. 2012; Bruenderman et al. 2002). Mussel shells were used to make buttons in the early 1900s when there was a large population of mussels in the Mississippi River. The population started to rapidly decline until the 1940s, when plastics were developed and the use of shells to make buttons stopped. The nacre of mussels can also be used to culture pearls. Beads of nacre are cut from shells and inserted into oysters. The beads irritate the oysters, causing them to secrete chemicals over the nacre pieces, and after two to four years, a cultured pearl will be ready.

Life Cycle, Reproduction, and Biology of Mussels

While at first glance mussels appear to be just shells, they actually are live animals with a unique life cycle (McMurray et al. 2012). To start reproduction, grown males release sperm into the water. As females filter water, they collect the sperm through their incurrent siphons (Bruenderman et al. 2002). The sperm go to their eggs, which are in their gill chambers. Then the eggs develop into glochidia, which are tiny larvae. (See step 1.)

The glochidia, which are parasitic and lack internal organs, require a host organism such as a fish to get needed nutrients (McMurray et al. 2012). Various mechanisms of obtaining glochidia hosts are used by different mussel species. For example, some mussels send out conglutinates, which are clumps of glochidia and other unfertilized eggs. The conglutinates, which look like prey, are eaten by the host fish. In contrast, the Lampsilis genus uses lures that look like the prey of the host fish. For example, some of the species use lures that look like crayfish to attract bass or walleye hosts. When the host fish sees the lure, it goes to it and inhales the glochidia. Some mussels can use many different host species, while others must use a particular species (Bauer et al. 2001. 384). Regardless of mechanism, the glochidia always attach to the gills or fins of the host fish (Bruenderman et al. 2002). (See step 2.) If the glochidia does not attach to a host, they die (Buchanan 1979. 2).

After a few days to a few weeks, the glochidia have developed into juvenile mussels capable of functioning independently, and they leave their hosts (McMurray et al. 2012). They usually do not harm their hosts. (See step 3.) When they leave their host fish, the developed juvenile mussels drop into their habitats. If the habitats are on strong ground that is always underwater, the mussels have a higher chance of surviving, becoming adults, and reproducing to start the cycle again. (See step 4.) Species with thinner shells can live to be four to ten years old, while species with thicker shells live to be twenty to forty years old (Buchanan 1979. 2).

Most of the time adult mussels are sessile, or stationary, but sometimes they will move (Nordsieck 2016). Adult mussels have an organ called the foot, which usually functions as an anchor to keep the mussel in place. However, the foot can move the mussel through the substrate, or the material on the bed of the water body, by advancing forward and then pulling the rest of the shell along with it.

Mussels in the Food Chain

Mussels filter feed using gills on either side of their foot, which is most of their body (Bauer et al. 2001. 383). The foot has two siphons, an incurrent siphon and an excurrent siphon (McMurray et al. 2012). Water enters the incurrent siphon and is sent over the gills. The gills extract oxygen for breathing and algae and other pieces of organic matter for food to go to the mussel’s stomach (Bruenderman et al. 2002). The rest of the water, including sediment and other pollutants, leaves through the excurrent siphon. Pseudofeces, or the undigested waste of the mussel, also leave through the excurrent siphon. The pseudofeces provide a food source to other organisms in the ecosystem.

Mussels are a good food source for many animals, including raccoons, minks, muskrats, otters, waterfowl, and fish (Bruenderman et al. 2002). People also can eat mussels, although many people tend to prefer saltwater mussels over the freshwater mussels found in Missouri. The freshwater mussels in Missouri have tougher meat and store more contaminants than saltwater mussels.

Mussel Habitat and Location

Mussels live in bodies of water (McMurray et al. 2012). Most live in flowing water, including rivers and streams, but some can live in still water, such as lakes, ponds, and reservoirs. Some move by burrowing, while others stay in one spot. Different species can live together without problems because they have similar habitat needs. Mussels usually live in stable areas of the substrate, meaning that there is a firm material or mix of materials that is always underwater. Mussels are usually not found in unstable areas because they are more likely to be washed away. In general, mussels tend to be found in downstream areas where branches of streams and rivers come together.

Mussels can be divided into four regions in Missouri based on location: the Ozark region, the Prairie region, the Lowland region, and the Big River region (Bruenderman et al. 2002). The Ozark region covers most of the southern half of the state. It has bodies of water draining from the Ozark mountains that are characterized as fast and clean, with sand and gravel riverbed habitats. Therefore, the Ozark region has the greatest diversity of species. The Prairie region includes most of the north half of Missouri. It has less diversity, and includes mud and clay riverbed habitats. The Lowland region has had more human activity and alterations to the landscape, but it still supports mussels that live in sand, mud, and clay habitats, and it has many ditches as well as streams and rivers. The Big River region winds throughout the state and contains the Mississippi and Missouri Rivers. Human activity on these rivers has led to a decline in diversity but the region still has mussels that live in mud, sand, and gravel riverbed habitats.

Shell Characteristics

The spreadsheet attached below covers many physical characteristics of mussel shells. Thickness, shape, and texture all have to do with the overall appearance of the shell (McMurray et al. 2012). The guide goes over the lateral and pseudocardinal teeth, which are located on the inside of the shell by the hinge, where one side of the shell connects to the other side. The lateral teeth, or hinge teeth, run along the shell parallel to the hinge, while the pseudocardinal teeth are rounder and help the shell stay closed. (Bowers-Altman, How to Identify Mussels). The spreadsheet also covers the beak cavity, which is located inside the shell and extends back into the umbo, or the hump that is by the hinge. The beak cavity can be a range of depths, which can help in identifying species.

The characteristic colors of the periostracum, periostracum rays, and nacre are also covered in the spreadsheet. The periostracum, or the outer covering of the shell, can be a wide range of colors (McMurray et al. 2012). The periostracum rays are lines that radiate out from the umbo perpendicular to the growth lines, which are concentric rings around the umbo. Some species or individuals within species do not have periostracum rays. A species can have a wide range of periostracum and periostracum ray colors, but the colors can still be useful when identifying species. The last physical characteristic that the spreadsheet covers is the nacre color. The nacre is the inside covering of the shell, and can be a variety of colors and is often iridescent. It is usually a lighter color than the periostracum.

It is important to remember that many species appear similar and even individuals within a species can vary widely, so accurate identification of mussels can be quite difficult (McMurray et al. 2012).

Human Effects on Mussel Decline

Changes in water quality and water movement can have drastic negative effects on mussel populations (McMurray et al. 2012). The creation of dams and reservoirs eliminates habitats for mussels that live in flowing water. Dams also change the conditions of the river downstream, including the temperature and the species of host fish available, making the habitat unsuitable for mussels species that originally lived there. Human activities that destabilize river and stream beds also make habitats unsuitable for many mussel species. Those activities include dredging, channelization, mining, and logging. Pollution reduces water quality and can harm or kill species. Sediment from increased agricultural production and cleared land buries mussels, and chemicals, heavy metals, and ammonia from pollutants such as fertilizer harm or kill species. Invasive species that have been introduced to ecosystems on boating equipment used in multiple bodies of water can take resources away from native species as well. All of these actions lead to mussel habitats that have been degraded.

Species Diversity and Conservation Status in Missouri

In the Guide to Missouri Mussels Spreadsheet below, there are 65 native species found in Missouri, four species possibly found in Missouri, and two invasive species, based on data from 2012 (McMurray et al. 2012). However, the numbers are always changing as new discoveries are made and others go extinct. The species are highly diverse because there are many rivers in Missouri with different ecosystems. The river systems coming from the Ozarks show great diversity.

Nine species statuses are applied to the mussels in the Missouri Department of Conservation’s A Guide to Missouri’s Freshwater Mussels: federal endangered, federal candidate, state endangered, species of conservation concern, common, common but restricted, undetermined, unknown, and invasive (McMurray et al. 2012). The first two are national statuses, applying to species that are nationally recognized as in danger of extinction or possibly going to become recognized as in danger of extinction. The next two statuses are applied by the state. State endangered species are endangered in Missouri, while species of conservation concern are critically imperiled, imperiled, or vulnerable. Common species are found throughout the state and common, but restricted species are commonly found only in certain areas of Missouri. Undetermined species are found in Missouri, but their conservation status is unknown, while unknown species have been found in Missouri, but there is not much else information about them. Invasive species are not native to Missouri, and usually cause damage.

See the table below for 2012 status statistics. Note that some species have multiple classifications. For example, 42% of the species in Missouri are species of conservation concern, including the 20% which are in danger of extinction (McMurray et al. 2012). See more information below in the Guide to Missouri Mussels Spreadsheet for statuses for specific species.

Status

Number of Species in 2012

Federal Endangered

9

Federal Candidates

2

Species of Conservation Concern

30

State Endangered

10

Common

27

Common, but restricted

8

Undetermined

1

Unknown

3

Invasive

2

Common Mussels In Missouri

Common species tend to occur around the eastern and southern parts of the state, especially along the Mississippi River, Missouri River, Osage River, St. Francis River, Gasconade River, and Meramec River (McMurray et al. 2012). Some of the most common genuses found in Missouri include the Lampsilis genus (8 species in Missouri), Quadrula genus (6 species in Missouri), and Potamilus genus (4 species in Missouri).

Examples of species in the common geniuses: the Fatmucket (Lampsilis siliquoidea), the Monkeyface (Quadrula metanevra), and the Bluefer (Potamilus purpuratus): Copyright: Photos by Jim Rathert, Bruenderman et al. 2002.

Invasive Species

Invasive species are nonnative to the ecosystem and compete with native species for resources and space (McMurray et al. 2012). In Missouri, there are three invasive species that affect mussels: the Asian clam, the zebra mussel, and the quagga mussel. The invasive species are less complex than mussels and are related to the native pea clam. The Asian clam entered the United States around the 1930s and quickly spread. They can live in a wide range of habitats and reach high densities of up to 10,000 clams per square meter, and when they die, large amounts of ammonia are released which reduces water quality and harms native mussels. Zebra mussels entered the country around the 1980s on ships from Europe, and spread quickly by traveling downstream and attaching to equipment and other things that move between waterbodies. They are now spread throughout many Missouri rivers, lakes, and reservoirs. Both zebra and quagga mussels starve, suffocate, and crowd out native species, which has led to the decline of native species. Two ways to prevent the spread of invasive species are to “Clean, drain, and dry” equipment used in water and to throw out bait after it is used in one body of water.

Observing, Reporting, and Collecting Mussels

It is easiest to find dead shells along banks of water bodies when the water level is low (McMurray et al. 2012). To find live mussels, you must search by wading, snorkeling, or scuba diving. If you pick up a mussel to observe it, you must return it to the exact location where it was, partially embedded in the ground, with its hinge side (where the two shells are joined) pointing up. If you think you have found something of interest, take photographs, note the location, and report to a Missouri Department of Conservation Regional Office.

With a Resident or Nonresident Fishing Permit, you can collect some mussel species, but if you cannot identify species, you should not collect them (McMurray et al. 2012). You can collect 5 dead mussels a day and as many Asian clams as you want. You cannot collect Missouri Endangered Species or Species of Conservation Concern without written permission from the  Conservation Department. You also cannot collect zebra mussels or quagga mussels. There are also some restrictions that apply only to certain areas, so check all restrictions before collecting.

Research About Mussels

Recent research has been done by Jo Ellen Hinck, et al., in 2012 on the mussel populations in the Meramec River basin in the paper Spatial and Temporal Trends of Freshwater Mussel Assemblages in the Meramec River Basin, Missouri, USA (Hinck 2012). The Meramec River Basin includes the Big River, Bourbeuse River, and Meramec River. Researchers sampled mussel populations by collecting mussels by wading, snorkeling, and diving for set amounts of time in each location. They found an overall decrease in mussel populations and diversity between 1978 and 1997, especially in the Bourbeuse and Meramec Rivers, while the Big River did not have as much decline in diversity. The mussel populations became extinct in some areas of the rivers faster than they could recolonize in other places. However, the researchers found that one region of the Meramec River actually had an increase in diversity. They propose that changes such as the increased presence of large rock face may have improved the habitat for some species of mussels. They found that the decline in populations of mussels was often due to loss of habitat due to muddier rivers, unstable river beds, and erosion.

Another recent research paper, Threats of Habitat and Water-Quality Degradation to Mussel Diversity in the Meramec River Basin, Missouri, USA, also by Jo Ellen Hinck, et al., in 2011, explores the parameters to prioritize to minimize harm to mussel populations (Hinck 2011). Research has shown that mussel populations are declining, so it is important to find parameters to work on that will help the most. Hinck and coworkers found that water quality parameters are the most important to control, specifically levels of chemicals such as ammonia, copper, and pesticides, as well as the water temperature. To address and reduce the decline of mussel populations, they recommend long term programs to monitor mussel populations and the important parameters, models to predict mussel population distribution, changes to wastewater treatment, and changes to land use around the mussels.

Mussels of Missouri Field Card

Download and print a Mussels of Missouri Field Card here.

Citations.

Guide to Missouri Mussels Spreadsheet

The Guide to Missouri Mussels Spreadsheet allows you to search for characteristics of a particular species of mussel to identify them. It also allows you to sort the data to identify mussel species that share characteristics. The second page of the spreadsheet includes the abbreviations used in the first page.

To view and download the spreadsheet, click here. Data from McMurray et al. 2012 and Bruenderman et al. 2002.

To use the spreadsheet, download the sheet to organize it yourself. Upon downloading, use the sort feature of the application to sort by characteristic you are interested in. To sort, select all of the data, click on the data menu, and click sort. Then choose the column that corresponds to the characteristic you would like to sort by. See this link for more instructions on how to sort spreadsheets. An “x” in a box indicates that the species has that characteristic. See below for more information as well as abbreviations used in the spreadsheet. The abbreviations are also listed in the second page of the spreadsheet. It is possible to sort the sheet by the following:

  • Common name
  • Scientific name to see which species are in the same genus
  • Protection status (see below for more information)
  • Who discovered the species
  • Year discovered
  • Similar/related species
  • Conservation Status
  • Range of shell length for adults
  • Location by region
  • Habitat
  • Water Body
    • River/flowing water
    • Lakes/still water
    • Current Speed
  • Ground Material
  • Physical Appearance
    • Shell Thickness
    • Shell Shape
    • Shell Texture
    • Lateral Teeth
    • Pseudocardinal Teeth
    • Beak Cavity
    • Periostracum
    • Periostracum Rays
    • Nacre

Conservation Status

The status abbreviations and definitions used by the Missouri Conservation Department’s A Guide to Missouri’s Freshwater Mussels are as follows. Some species fall under multiple statuses. Statuses also change over time. The data in this spreadsheet are from 2012. These statuses are from the federal and state governments.

  • Federal Endangered (FE): species in danger of extinction through most or all of range, recognized by the U.S. Fish and Wildlife Service
  • Federal Candidate (FC): species in the evaluation process to add to list of endangered/threatened species
  • State Endangered (SE): species is endangered in Missouri, recognized by the Wildlife Code of Missouri
  • Species of Conservation Concern (SCC): in Missouri, species is “Critically Imperiled,” “Imperiled,” or “Vulnerable”
  • Common (C): species found in its habitat, can be widespread
  • Common, but restricted (CR): species is common but restricted to certain location
  • Undetermined (Ud): species occurs in Missouri but status is unknown because there is not enough data
  • Unknown (Uk): species has been reported in Missouri, but it is unknown if it still occurs in Missouri
  • Invasive (I): species is nonnative to Missouri

(McMurray et al. 2012)

Scientific Name:

The scientific name listed has two parts, the genus, which is listed first and is capitalized, and the species, which is listed second and lowercase.

Location: (Bruenderman et al. 2002)

As previously mentioned, Missouri can be divided into four regions for where different species of mussels are located: the Ozark region, the prairie region, the lowland region, and the big river region. Note: For the species classified as unknown or undetermined, there is not enough reliable data to know their exact locations. Therefore, a question mark has been used instead of an x in the spreadsheet for those species. The spreadsheet abbreviations are: Prairie region (Pra), Ozark region (Ozk), Lowland region (Low), and Big River region (BRiv).

Habitat: (McMurray et al. 2012)

The habitats have been divided up into categories based on water body type, current, and ground material.

Water bodies with flowing water, arranged in order of size, are: large rivers (Riv-L), medium rivers (Riv-M), small rivers (Riv-S), large streams (Str-L), medium streams (Str-M), small streams (Str-S), and creeks (Crk). Other flowing water habitats include backwaters of large rivers (Riv-L, BW), headwaters of medium rivers (Riv-M, HW), and oxbows (Oxb).

Water bodies with still water include: oxbow lakes (Lk, oxb), lakes (Lk), ponds (Pd), reservoirs (Rsv), bluff pools (BP), sloughs (Sl), ditches (Dit), and slack water (SlW).

Current variations, from slow to fast, include: still water (StW), slow current (Cur-Sl), moderate current (Cur-Mod), and fast current (Cur-F).

Ground materials include the following:

  • Boulders (Bld)
  • Under large flat rocks (FR)
  • Dead shells of larger species (DS)
  • Gravel substrates (Subs-Grv)
  • Gravel-sand substrates (Subs-Grv-Sand)
  • Sand substrates (Subs-Sand)
  • Mud substrates (Subs-Mud)
  • Mud-gravel substrates (Subs-Mud-Grv)
  • Cobble (Cob)
  • Coarse gravel (Grv-Coar)
  • Gravel (Grv)
  • Fine gravel (Grv-Fine)
  • Sand (Sand)
  • Fine sand (Sand-Fine)
  • Mud (Mud)
  • Fine mud (Mud-Fine
  • Stable gravel (Grv-Stb)
  • Stable mud (Mud-Stb)
  • Firm sand (Sand-Firm)
  • Mud-gravel mix (Mud-Grv)
  • Gravel-sand mix (Grv-Sand)

Physical Characteristics of Mussel Shells: (McMurray et al. 2012)

Shell Thickness:

Thin (Thin), medium (Med), moderately thick (Mod Th), thick (Th), fragile (Fra), solid/sturdy (Sol)

Shell Shape:

Circular (Cir), elliptical (Ell), oval (Oval), quadrate (Quad), rectangular (Rec), rhomboidal (Rhom), round (Rou), elongated (Elg), trapezoidal (Trap), triangular (Tri), arched (Arch), compressed (Comp), inflated (Infl), oblong (Obl)

Shell Texture:

Smooth (Smo), flutings (Flut), wrinkled (Wrin), rough (Rou), knobby (Knob), ridges/folds (Rid)

Lateral Teeth:

Absent (Abs), poorly-developed (PDev), single flange (SFla), short (Sho), long (Lng), large (Lrg), straight (Str), heavy (Hvy), well-defined/well-developed (WDef), thin (Thin), sharp (Shp), rough (Rou), curved (Crv)

Pseudocardinal Teeth:

Absent (Abs), Poorly-developed (PDev), reduced (Red), small (Sma), stout (Sto), thin (Thin), weak (Weak), moderate (Mod), distinct (Dist), large (Lrg), well-defined/well-developed (WDef), elevated (Elev), rough (Rou), conical (Con), triangular (Tri), sharp (Shp)

Beak Cavity:

None (Non), shallow (Shal), moderate (Mod), moderately deep (ModD), deep (Deep), broad (Bro), salmon (Sal)

Periostracum:

Yellow (Yel), light green (LGrn), green (Grn), light brown (LBrn), tan (Tan), chestnut (Che), Brown (Brn), Black (Blk), dark (Dark), gray (Gray), white (Wht), cream (Crm), silver (Slv), metallic (Met), peeling (Peel), dull (Dull)

Periostracum rays:

Absent (Abs), green (Grn), blue (Blu), brown (Brn), dark brown (DBrn), black (Blk), multi-colored (MCol), speckled (Spec), zigzag (Zig), wavy (Wav), faint (Fai), splotchy (Spl), thin (Thin)

Nacre:

Pink (Pnk), salmon (Sal), purple (Pur), Bronze (Brz), Copper (Cop), Bluish-white (BW), white (Wht), cream (Crm), silver (Slv), iridescent (Iri)

Sources:

Unless otherwise noted, all information comes from:

McMurray, Stephen E., et al. A Guide to Missouri’s Freshwater Mussels. Missouri Conservation Department, 2012.

Additional Sources:

Bauer, Gerhard, and Klaus Wachtler. Ecology and Evolution of the Freshwater Mussels Unionoida. Springer-Verlag Berlin Heidelberg, 2001. Print.

Bowers-Altman, Jeannette. How to Identify Mussels. New Jersey Endangered and Nongame Species Program, unknown date.

Bruenderman, Sue, et. al. Missouri’s Freshwater Mussels. Conservation Commission of the State of Missouri, 2002.

Buchanan, Alan C. Mussels (Naiades) of the Meramec River Basin, Missouri. Missouri Department of Conservation, 1979.

Hinck, Jo Ellen, et al. “Spatial and Temporal Trends of Freshwater Mussel Assemblages in the Meramec River Basin, Missouri, USA.” Journal of Fish and Wildlife Management, Volume 3, Issue 2, pages 319-331.

Hinck, Jo Ellen, et al. “Threats of Habitat and Water Quality Degradation to Mussel Diversity in the Meramec River Basin, Missouri, USA.” United States Geologic Survey, 2011-1125, pages 1-18.

Nordsieck, Robert. “Mussels and Clams.” The Living World of Molluscs, 13 Dec. 2016, http://www.molluscs.at/bivalvia/.

This page was written and created by Jessica Rehmann, 2016.

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