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Recovery Strategy for the Northern Riffleshell, Snuffbox, Round Pigtoe, Mudpuppy Mussel and Rayed Bean in Canada (Final)


5. Species Information – Rayed Bean


Common Name: Rayed Bean

Scientific Name: Villosa fabalis

COSEWIC Status: Endangered

COSEWIC Reason for designation1: The Rayed Bean was once widely distributed throughout its original range in North America, but has declined significantly in distribution and abundance in recent years. In Canada, it now occurs only in a 45-km reach of the East Sydenham River, where it is threatened by siltation and pollution associated with intensifying agricultural activities.

Occurrence: Ontario

COSEWIC Status history: Designated Endangered in 1999

1 A new population was confirmed in the North Thames River in 2004.

The Rayed Bean is a very small freshwater mussel with a semi-elliptical shape. Females are more broadly rounded and inflated than males. The periostracum is light or dark green and covered with wide or narrow, wavy, darker green rays that are clearly apparent except in old specimens. The beaks are narrow, slightly elevated above the hinge line and not excavated. The hinge teeth are relatively heavy with erect, pyramidal, serrated pseudocardinals, short laterals with diagonal serrations, and a thick interdentum.

The genus Villosa is represented by 18 species in North America, only two of which occur in Canada. It was historically known from Alabama, Illinois, Indiana, Tennessee, New York, Virginia, West Virginia and Ontario. It was widely distributed throughout the Ohio and Tennessee drainages, western Lake Erie, Lake St. Clair and the St. Clair River and their tributaries. In Canada, the Rayed Bean was known from western Lake Erie, the Detroit, Sydenham and Thames rivers.

Figure 13. The Rayed Bean Villosa fabalis. Photo Credit: S. Staton, Environment Canada.
Figure 13. The Rayed Bean Villosa fabalis. Photo Credit: S. Staton, Environment Canada.

Although population trends are difficult to quantify due to a lack of numerical data, the species is generally recognized to have significantly declined throughout its range in recent years. In the United States, the Rayed Bean is now most frequently found in the Ohio drainage. It is currently ranked as S1 in most areas by NatureServe. In Canada, this species has been extirpated from Lake Erie and the Detroit River and until recently was believed to be restricted to a 50 km reach of the East Sydenham River. However, a single live specimen and one fresh shell were recorded from the North Thames River upstream of Fanshawe reservoir in 2004.

Distribution

Global Range

The Rayed Bean was once widely but discontinuously distributed throughout the Ohio and Tennessee River systems, western Lake Erie and its tributaries and in tributaries to the St. Clair River and Lake St. Clair. In the U.S. the Rayed Bean currently occurs in Alabama, Indiana, Kentucky, Michigan, New York, Ohio, Pennsylvania, Tennessee and West Virginia. In Canada, it occurs only in southern Ontario.

Canadian Range

The current Canadian distribution of the Rayed Bean is limited to a 50 km stretch of the East Sydenham River and a small section of the North Thames River

Percent of Global Range in Canada

Less than 10% of the species' global distribution is currently found in Canada.

Distribution Trend

In Canada, the current range of the Rayed Bean has changed little over time. It is found throughout a 50 km reach of the East Sydenham River where it is successfully reproducing (Woolnough and Mackie, 2001). A single live specimen and one fresh shell were recorded from the North Thames River upstream of Fanshawe Reservoir during 2004 (T. Morris, unpublished data).

Population Abundance

Global Range

In the United States the Rayed Bean currently occurs in Alabama, Indiana, Kentucky, Michigan, New York, Ohio, Pennsylvania, Tennessee and West Virginia. In Canada, it occurs only in southwestern. Ontario.

Canadian Range

The current Canadian distribution of the Rayed Bean is limited to a 50-km stretch of the East Sydenham River and a small section of the North Thames River.

Percent of Global Abundance in Canada

Less that 20% of the species' global distribution is currently found in Canada.

Population Trend

The Rayed Bean is considered to be a rare species, however, abundant populations have recently been seen in parts of Ohio and Pennsylvania. Other studies in the United States indicate that the species is in decline. The Rayed Bean is presumed extirpated from Illinois and Virginia. In Canada, populations of the Rayed Bean have been reported from the Detroit River and Lake Erie near Pelee Island. These locations have not reported Rayed Bean sightings since 1986 and the populations are assumed to be extirpated. It is impossible to estimate trends in the Sydenham or Thames river populations as historical abundance estimates are not available.

Figure 14. Global distribution of the Rayed Bean.
Figure 14. Global distribution of the Rayed Bean.

 

Figure 15. Distribution of the Rayed Bean in Canada.
Figure 15. Distribution of the Rayed Bean in Canada.

Biological Limiting Factors

Reproductive Attributes

The reproductive biology of the Rayed Bean follows the general reproductive biology of most mussels. During spawning, male mussels release sperm into the water column and females filter it out of the water with their gills. Fertilization is then able to occur in specialized regions of the gills known as marsupia and are released by the female into the water column to undergo a period of parasitism on a suitable host fish species. The Rayed Bean is a long-term brooder that holds its glochidia over winter for spring release. Further development to the juvenile stage can not continue without a period of encystment on the host.

The glochidia are subspatulate or rounded with a straight hinge line (Bogan and Parmalee 1983; Hoggarth 1993). They are higher than long indicating that they are gill parasites.

To determine host fishes for the Rayed Bean, twelve host species underwent infestation experiments in the laboratory at the University of Guelph from 2002 – 2005. The Rayed Bean successfully transformed on seven of these: the brook stickleback, greenside darter (Etheostoma blennioides), Johnny darter, logperch, rainbow darter, mottled sculpin (Cottus bairdii), largemouth bass (Woolnough 2002; McNichols et al. 2004).

Dispersal

Like most freshwater mussels, the Rayed Bean has very limited dispersal abilities. The Rayed Bean adults are essentially sessile with movement limited to only a few meters on the river/lake bottom. Although adult movement can be directed upstream or downstream, studies have found a net downstream movement through time (Balfour and Smock 1995; Villella et al. 2004). The primary means for large scale dispersal, upstream movement, and the invasion of new habitat or evasion of deteriorating habitat, is limited to the encysted glochidial stage on the host fish.