Threehorn Wartyback
Obliquaria reflexa
Species Description
The Threehorn Wartyback is adorned with a single row of 2-5 prominent knobs or “horns” extending down its thick, triangular shell. Their shell is typically tan to brown, sometimes with narrow green rays. They are a medium-sized mussel, reaching 4 to 5.5cm and can live for 18 years.
Lifecycle
As with all unionid mussel species, they depend on host fish species to complete their lifecycle. Females release glochidia encased in a package of mucous know as conglutinates. When a fish ingests a conglutinate, it ruptures and the glochidia attach to the gills where they develop and drop off as juvenile mussels. The Common Shiner and Longnose Dace have been identified as the most likely fish hosts for Threehorn Wartyback in Canada.
Habitat
The preferred habitat of these horned filter feeders are large rivers with moderate flow and substrates that range from gravel, sand, or mud. They have been detected at depths of 7m but are more commonly found at water depths less than 2m.
Distribution
In Canada, the rare Threehorn Wartyback is found in the lower Great Lakes region of Ontario. The species is now restricted to only three rivers in Canada, the Sydenham, Thames, and Grand rivers but, historically, it also lived in the waters of Lake St. Clair, the Detroit River, and Lake Erie.
Threehorn Wartyback was first recorded on the East Sydenham River in 1998 by DFO and, more recently, was first documented on the North Branch of the Sydenham in 2018 by the SCRCA.
Threats to the Threehorn Wartyback
One of the most significant threats to Threehorn Wartyback is pollution entering watercourses resulting from urban and agriculture land use including excess sediment that can smother mussel beds, excess nutrients that can result in low oxygen levels, and toxic substances. Invasive species like Zebra Mussels and the Round Goby has negative impacts. Zebra Mussels attach to native mussels and inhibit feeding, respiration, and reproduction, while the Round Goby is a voracious bottom feeder consuming benthic macroinvertebrates, fish eggs, and juvenile mussels. Round Goby also disrupt the native fish community, which limits successful juvenile mussel development. The combination of these and other threats can have serious damaging impacts on Threehorn Wartyback populations.