Snuffbox
Epioblasma triquetra
Beneath the waters of the Sydenham River lives a unique and rare mussel species known as the Snuffbox. There are few mussels that share resemblance to the Snuffbox – it is a small, triangular mussel that grows to a maximum of 7.5cm and it has a strong posterior ridge. The Snuffbox’s thick, yellow shell is decorated with dark green rays and blotches that resemble dripping paint, which could lead one to believe that each one was hand painted. They are sexually dimorphic, meaning the males and females look different, the females are smaller with shells that are more inflated and slightly more elongated. The bottom edge of the shell is curved in males whereas females have a small indent and denticles on the ventral margin of their shell.
The uniqueness of the Snuffbox does not end with its appearance, it has also adapted a fascinating reproductive strategy.
Like the other native freshwater mussels in the Sydenham, the Snuffbox requires a host fish to nourish their parasitic larvae, known as glochidia, and help them disperse to new areas of habitat.
Snuffbox and Northern Riffleshell are the only two species in the Sydenham that belong to the genus Epioblasma, which use a unique strategy to ensure their glochidia reach their host – they actually capture their host fish.
The Snuffbox is a host specialist and has evolved a unique relationship with the native Logperch, a small, bottom-dwelling darter. Logperch feed along the river bottom on aquatic insect larvae, rolling stones in search of prey. On occasion, an unsuspecting Logperch will roll a female Snuffbox, who then snaps closed on the Logperch’s long snout, the female mussels have serrations on the edge of their shell, known as denticles, that help the mussel hold on to the host fish. The Logperch has evolved alongside the Snuffbox to have a strong, reinforced skull that can withstand the mussel clamping down on it. With the Logperch firmly grasped, the Snuffbox then expels glochidia, which attach to the fish’s gills. After several weeks of absorbing nutrients, the young mussels detach from their host and float down to the substrate below. The Snuffbox, like other unionids, can only move small distances so they rely on host fish species to carry the next generation to new parts of the river.
Snuffbox can be found in shallow riffle areas with clean, clear, fast-flowing water with a substrate consisting of gravel, sand, and rocks. They often bury themselves within the substrate or with only their posterior ridge exposed.
The Snuffbox is only found in two rivers in Canada, it is limited to a 93km stretch of the East Sydenham River and five sites in a 91km stretch of the Ausable River. Although, historically, the Snuffbox could also be found in the Grand, Niagara, and Thames rivers, Lake St. Clair and Lake Erie.
In 2020, the SCRCA surveyed mussels from a 4.5km section of the East Sydenham River – known Snuffbox habitat. Of the 1,689 live mussels detected, only 10 live Snuffboxes were found.
The Snuffbox is considered globally vulnerable and has been lost from 60% of its former range. Based on the change in catch rates over time, populations in the East Sydenham River seem to be declining. Like other unionids, Snuffbox face several threats, the most significant being siltation and pollution from agricultural and urban runoff, sediment can suffocate mussel beds. Invasive species like the Round Goby threaten mussels by feeding on juvenile mussels as well as impacting their host fish populations. The introduction of Zebra and Quagga mussels has also had devastating impacts on freshwater mussel communities in the Great Lakes.
© 2024 · St. Clair Region Conservation Authority - The Sydenham River Watershed