Obliquaria reflexa
Threehorn wartyback

Key Characteristics

The threehorn wartyback has a rounded, small to medium-sized shell (to 3 inches) that varies in color from shades of yellow and green to brown. This species is easily recognized by a central row of 1-4 large knobs on each valve in alternate positions.

Status and Rank

  • State Status: E
  • State Rank: S1
  • Global Rank: G5

Occurrences

County NameNumber of OccurrencesYear Last Observed
Allegan11936
Berrien1
Monroe42011
Ottawa41960
Saginaw1
St. Clair12011
Van Buren1
Wayne21936
Distribution map for Obliquaria reflexa

Updated 1/31/2017. Information is summarized from MNFI's database of rare species and community occurrences. Data may not reflect true distribution since much of the state has not been thoroughly surveyed.

Habitat

Most common in medium to large rivers, the three-horned wartyback occurs in slackwater conditions to swift currents, and substrates of gravel to muddy sand (Oesch 1995, Watters et al. 2009).This species has been found to be relatively tolerant of river impoundments (Grabarkiewicz and Davis 2008).

Specific Habitat Needs

needed in Mainstem Stream (3rd-4th order), Riffle, Mainstem Stream (3rd-4th order), Pool, Mainstem Stream (3rd-4th order), Run, River (5th-6th order), Riffle, River (5th-6th order), Pool, River (5th-6th order), Run, Great Lake, Littoral, Benthic, Great Lake, Pelagic, Benthic

Natural Community Types

Methodology

For each species, lists of natural communities were derived from review of the nearly 6,500 element occurrences in the MNFI database, in addition to herbarium label data for some taxa. In most cases, at least one specimen record exists for each listed natural community. For certain taxa, especially poorly collected or extirpated species of prairie and savanna habitats, natural community lists were derived from inferences from collection sites and habitat preferences in immediately adjacent states (particularly Indiana and Illinois). Natural communities are not listed for those species documented only from altered or ruderal habitats in Michigan, especially for taxa that occur in a variety of habitats outside of the state.

Natural communities are not listed in order of frequency of occurrence, but are rather derived from the full set of natural communities, organized by Ecological Group. In many cases, the general habitat descriptions should provide greater clarity and direction to the surveyor. In future versions of the Rare Species Explorer, we hope to incorporate natural community fidelity ranks for each taxon.

Management

Approximately 70% of North American unionids are in decline. Leading threats to this group include water quality degradation, alteration of physical habitat, host fish population declines, and invasive species introduction (Bringolf et al. 2007). The threehorn wartyback, along with other species in this group, exhibit high absorption rates for heavy metals and other contaminants found in herbicides, pesticides (Bringolf et al. 2007), industrial waste, and urban runoff (Levengood et al. 2004). Sedimentation of waterways can be harmful to a wide variety of freshwater organisms. Management of the threehorn wartyback, therefore, must include adhering to high water quality standards and the conservation of healthy habitat structure. Zebra mussels must be prevented from spreading to new waterways through the careful cleaning of fishing gear, boats and trailers, and scuba equipment in order to protect unionid populations from infestation.

Active Period

Gravid from first week of June to fourth week of August

Survey Methods

Visual and tactile search using scuba or glass-bottom buckets. Tactile search (by hand) is especially important where water turbidity and pebbles/rocks make visual detection difficult. After identification, live mussels should be planted back into the substrate anterior end down. Surveys should not take place after heavy rains or during periods of high water as these conditions can make detection much more difficult.  Methods of documenting survey effort include: searching a large measured area, e.g. 128m2; taking multiple quadrat samples; and recording search time (person hours).  For all methods, at least some excavation of substrate (by hand, 5-10cm down) should be done to detect buried mussels.  Searching a large measured area or timed searches are generally better for detecting rare species and generating a species list than quadrat sampling.  These two methods allow more types of microhabitats and a larger area to be covered.  Quadrat sampling is better suited for documenting changes in density and other statistical analyses at the site level (Strayer and Smith 2003).

Page Citation

Michigan Natural Features Inventory. 2007. Rare Species Explorer (Web Application). Available online at http://mnfi.anr.msu.edu/explorer [Accessed Jul 20, 2017]

References

Survey References

Technical References

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