Obovaria retusa

{{Short description|Species of bivalve}} {{Speciesbox | image = Obovaria retusa.jpg |image_caption=Dried valves | status = CR | status_system = IUCN2.3 | status_ref = <ref name="iucn status 16 November 2021">{{cite iucn |author=Bogan, A.E. |date=1996 |title=''Obovaria retusa'' |volume=1996 |article-number=e.T15020A4488592 |doi=10.2305/IUCN.UK.1996.RLTS.T15020A4488592.en |access-date=16 November 2021}}</ref> |status2=LE |status2_system=ESA |status2_ref=<ref name=ecos>{{cite web|url=https://ecos.fws.gov/ecp/species/4128|title=Ring pink (mussel) (''Obovaria retusa'')|website=Environmental Conservation Online System|publisher=U.S. Fish & Wildlife Service|access-date=2 December 2023}}</ref><ref name=fr54>{{Federal Register|54|40109}}</ref> | genus = Obovaria | species = retusa | authority = ([[Jean-Baptiste Lamarck|Lamarck]], 1819) | synonyms = *''Unio retusa'' Lamarck, 1819 *''Obovaria torsa'' Rafinesque, 1820 *''Unio incurvis'' Say, 1829 *''Obovaria torsa'' subsp. ''marginata'' Rafinesque, 1820 |synonyms_ref=<ref>{{ITIS|taxon=''Obovaria retusa'' (Lamarck, 1819)|id=80175|access-date=2 December 2023}}</ref> }} {{commons category}} '''''Obovaria retusa''''' is a rare species of [[freshwater mussel]] in the family [[Unionidae]], the river mussels. Its common names include '''golf stick pearly mussel''' and '''ring pink'''.

This mussel was native to [[Alabama]], [[Illinois]], [[Indiana]], [[Kentucky]], [[Ohio]], [[Pennsylvania]], [[Tennessee]], and [[West Virginia]]. By 1991 it was thought that there were about five populations remaining in Kentucky, Tennessee, and West Virginia. It is now thought to be [[Local extinction|extirpated]] from West Virginia, as the population there was a misidentification.<ref name=":7">Koch, Leroy, et al. "Ring Pink Obovaria Retusa (Lamarck, 1819) 5-Year Review: Summary and Evaluation ." Federal Register, U.S. Fish and Wildlife Service, 27 Apr. 2011 https://ecos.fws.gov/docs/tess/species_nonpublish/1732.pdf</ref> Only a few specimens of the species have been observed recently. If any viable populations remain, they will be located in the [[Green River (Kentucky)|Green River]] of Kentucky.

== General summary == The ring pink mussel (''Obovaria retusa'') is also referred to as the "golf stick pearly mussel" or "ring pink".<ref name=":0">Biggins, Richard G. "Ring Pink Mussel Recovery Plan." Ecos.fws.gov, U.S. Fish and Wildlife Service, 25 Mar. 1991, https://ecos.fws.gov/docs/recovery_plan/910325.pdf. </ref> Ring Pink mussels are [[freshwater bivalve]]s.<ref name="iucn status 16 November 2021"/> They are in the river mussel family [[Unionidae]]. Ring pink mussels are native to the eastern and southeastern regions of the United States. They are currently found in Alabama, Kentucky, and Tennessee.<ref name=":0" /> The U.S. Fish and Wildlife Service listed the ring pink mussel as an endangered species under the [[Endangered Species Act of 1973|Endangered Species Act]] in 1989.<ref name=fr54/> The species is still listed as endangered.<ref name=ecos/><ref name=":1">Koch, Leroy, et al. "Ring Pink Obovaria Retusa (Lamarck, 1819) 5-Year Review: Summary and Evaluation ." Federal Register, U.S. Fish and Wildlife Service, 25 Sept. 2019, https://ecos.fws.gov/docs/tess/species_nonpublish/2870.pdf</ref>

== Morphological description == The ring pink mussel was first described by the French naturalist Jean-Baptise Lamarck in 1819.<ref name=":0" /> This mussel has a medium to large shell. The shapes of its shells can range from oval to square.<ref>Bogan, Arthur E, and Paul W Parmalee. "Tennessee's Rare Wildlife - Volume II: The Mollusks." TDAR, National Archaeological Database, 16 July 2011, https://core.tdar.org/document/180780/tennessees-rare-wildlife-volume-ii-the-mollusks.</ref> The exterior of the shell ([[periostracum]]) does not have rays and has a yellow-green to brown color. Usually, older individuals are darker brown or black. The inner layer of the shell ([[nacre]]) has a salmon to deep purple color and a white border.<ref name=":0" />

== Life history == General [[Freshwater bivalve|freshwater mussel]] information supplements the current knowledge on the ring pink mussel. The ring pink mussel's [[Life history theory|life cycle and history]] are not well known.<ref name=":0" />

For freshwater mussels, males discharge their sperm into the water column. Females take their sperm in through their gills to fertilize the eggs. In typical freshwater mussel life cycles, the larvae develop into a life stage called [[Glochidium|glochidia]]. Pregnant females release glochidia from their gills. After release, these glochidia attach to the gills or scales of freshwater fish. Once attached to the fish, the larvae act as parasites for weeks to months. It is unknown if the ring pink mussel utilizes a specific fish species or is more generalist in their attachment.<ref name=":0" /> This [[Parasitism|parasitic]] attachment to the host fish determines their population distribution. During this time as a parasite they [[Metamorphosis|metamorphosize]] into juvenile mussels. Afterwards, they detach from their fish host. The juvenile mussels sink to the [[benthos]] and settle as free-living mussels. It takes an average of 2–9 years for a freshwater mussel to reach reproductive maturity. In some freshwater species, they may only spawn once in 7 years. The average lifespan of a freshwater mussel ranges from 60 – 70 years.<ref name=":2">Ortmann, A. E. 1909. The breeding season of Unionidae in Pennsylvania. Nautilus, 22(9):91-95; 22(10):99-103.</ref>

Ring pink mussels pregnant with [[Glochidium|glochidia]] have been observed in late August.<ref name=":2" /><ref name=":3">Ortmann, A. E. 1912. Notes upon the families and genera of the naiades. Annals Carnegie Mus., 8:222-365.</ref> Ring pink [[Glochidium|glochidia]] have been described as "rather large and hookless".<ref name=":3" />

Overall, ring pink mussels and other freshwater mussels are long-lived organisms. They exhibit [[Ovoviviparity|ovoviviparous]] reproduction and reach sexual maturity at a late stage. They have a low frequency of successful reproduction events.

== Ecology ==

=== Diet === The ring pink mussel's specific diet is unknown. Its diet likely does not differ from the diet of other freshwater mussels.<ref name=":0" /> Freshwater mussels' diets often comprise [[detritus]], [[diatom]]s, [[phytoplankton]], and [[zooplankton]].<ref name=":4">Churchill, E. P., Jr., and S. I. Lewis. 1924. Food and feeding in freshwater mussels. Bull. U.S. Bur. Fish. 39:439-471</ref>

=== Behavior === Little is known about the ring pink's reproductive behavior. Ring pink mussel mating is thought to resemble that of other freshwater mussels.<ref name=":0" /> Freshwater mussels typically exhibit burrowing behavior in juvenile stages.<ref>Gordon, Mark E, et al. "MUSSELS (BIVALVIA: UNIONOIDEA) OF THE CUMBERLAND RIVER Review of Life Histories and Ecological Relationships." Citeseerx.ist.psu.edu, U.S. Fish and Wildlife Service, July 1989, https://citeseer.ist.psu.edu/viewdoc/summary?doi=10.1.1.136.3720.</ref> See Life History section for more information. Since the ring pink mussel is a rare species, there have been few reports of its behavior in the wild.

=== Habitat === The ring pink mussel is found in medium to large rivers. They inhabit the silt, sand, and gravel substrate of these rivers.<ref name=":7" /> The ring pink does not frequent habitats deeper than about one meter.<ref>Downing, John A, et al. "Spatial Aggregation, Body Size, and Reproductive Success in the Freshwater Mussel Elliptio Complanata: Journal of the North American Benthological Society: Vol 12, No 2." Journals.uchicago.edu, Journal of the North American Benthological Society, 1 June 1993, https://www.journals.uchicago.edu/doi/abs/10.2307/1467344</ref>

=== Range === Historically, the ring pink mussel was native to the Ohio River and its [[Tributary|tributaries]] in Pennsylvania, West Virginia, Ohio, Indiana, Illinois, Kentucky, Tennessee, and Alabama.<ref name=":0" /> Its range has decreased due to damming. The Ring Pink mussel is currently found or believed to be found in Alabama, Tennessee, and Kentucky.<ref>Lamarck. "Obovaria Retusa (Lamarck, 1819)." GBIF, 1819, https://www.gbif.org/species/2288366.</ref>

== Conservation ==

=== Population size === Construction of dams on large rivers has caused declining numbers of the ring pink.<ref name=":0" /> In the ring pink mussel 1991 recovery plan, five known populations of ring pink mussels were reported. However, few sightings of the species have been noted since the early 1990s.<ref name=":5">Mussel Life Cycle - Minnesota State University, Mankato. https://mrbdc.mnsu.edu/sites/mrbdc.mnsu.edu/files/public/pdf/askexpert/mussel_lifecycle.pdf.</ref> In the past 15 years, only two live ring pink individuals have been observed.<ref name=":5" /> Both sightings were in the Green River in Kentucky.<ref name=":5" /> It is hard to find the mussel through typical surveying methods, so small populations of the ring pink may still exist.<ref name=":5" />

The 1991 ring pink recovery plan noted that the five populations in existence were old and most likely non-reproducing.<ref name=":0" /> A recent review by the U.S. Fish and Wildlife Services asserts that no viable populations currently exist.<ref name=":7"/> Studies have shown that decreased densities of freshwater mussels may lead to decreased fertilization and reproduction, possibly explaining the sudden drop in species numbers.<ref name=":4" /> Seeing that there are no reproducing populations, it is unlikely that population size will increase.

=== Past and current geographical distribution === In the past, the ring pink mussel was widely distributed among the Ohio River and its tributaries. These rivers span Pennsylvania, West Virginia, Ohio, Illinois, Indiana, Kentucky, Tennessee, and Alabama. By 1991, only five populations of the ring pink mussel were known and occurred in Kentucky, Tennessee, and West Virginia.<ref name=":0" /> Since 1998, there have only been four sightings of the ring pink at the Green River in Kentucky. As of 2019, it is believed that a small population of ring pinks in the Green River is the only population in existence. There is some speculation that ring pink individuals may occur in the Cumberland and Tennessee Rivers as well.<ref name=":7" />

=== Major threats and human impact === The ring pink mussel is thought to be sensitive to habitat degradation. In the 1991 Ring Pink Recovery Plan, the U.S. Fish and Wildlife Services cite dam construction as a major cause of Ring Pink endangerment. Dam construction reduces the availability of preferred gravel and sand habitat for the Ring Pink. Dams also disrupt the life cycle of the ring pink mussel by limiting the availability of host fish for Ring Pink larvae. [[Dredging|Gravel dredging]] and channel maintenance also contribute to habitat loss for the Ring Pink mussel.<ref name=":0" />

Besides habitat destruction, commercial mussel fishing also poses a threat to the Ring Pink mussel. The mussel is sometimes taken during commercial mussel fishing of other species.<ref name=":0" />

== Listing under the ESA == As of September 29, 1989, the species is listed as endangered under the Endangered Species Act.<ref name=":0" /> It was also listed as a small experimental, non-essential population established on October 15, 2007, in some portions of the [[French Broad River]] and [[Holston River]] in Tennessee.<ref name=":0" />

== 5-year reviews == The U.S. Fish and Wildlife Services has completed and published two 5-year reviews. These reviews determine species status and recovery achievements.<ref name=":0" /> The U.S. Fish and Wildlife Services publicly announced a review of the Ring Pink Mussel on November 6, 1991.<ref name="Interior 1991">Department of the Interior; Endangered and Threatened Wildlife and Plants; 5-Year Review of Listed Species; Proposed Rule 56 Fed. Reg. 215 (November 6, 1991).</ref> This document provided no in-depth evaluation of species' recovery,<ref name=":7" /> and no 5-year review was published in the decade after this notification.<ref name=":0" />

Another review was published in 2011.<ref name=":7"/> The review conducted a five-factor analysis of threats to the ring pink's habitat. Habitat threats include overutilization, disease, predation, regulations, and other anthropogenic and natural factors affecting its existence. Only three individuals had been found between 1998 and 2011. Based on these results, the 2011 5-year review asserted that the ring pink should remain an endangered species.<ref name=":7" />

Another public notice of a 5-year review was announced on June 20, 2017, in the ''Federal Register''.<ref>{{Federal Register|82|29916}}</ref> This review was published in 2019. This review presented a similar five-factor analysis and stated no need for change in listing.<ref name=":1"/>

Both reviews assert there is a high threat to the ring pink species. Experts consider recovery potential as low.<ref name=":1" /><ref name=":7" /> See "Recovery Plan" section for more information on recommendations for future action.

== Species Status Assessment == No Species Status Assessments are currently available for this species.<ref name="Interior 1991"/>

== Recovery Plan == The aim of the U.S. Fish and Wildlife Recovery Plan is to downlist the ring pink mussel from endangered to threatened.<ref name=":0" /> Total recovery is not thought to be possible. The downlisting date cannot be estimated at this time. Mussels do not reproduce until about age 5. More than 10 years are needed to document reproduction and assess viability. Experts must study the impact of commercial fisheries. Some river beaches may need to be declared mussel sanctuaries. Recommendations for future actions acknowledge the limited success in finding individuals.<ref name=":5" /> Experts could perform surveys in the Tennessee and Cumberland rivers to find sites with suitable habitat. One suggestion was to determine the fish host(s) of the ring pink and propagate the species. This way, propagated juveniles could be moved to areas with mussel assemblages. The round hickorynut, another mollusk that could be considered a potential proxy, is hosted by the [[eastern sand darter]] (''Ammocrypta pellucida''). This may indicate that the ring pink's host is the western sand darter (''[[Ammocrypta clara]]'') and/or ''Ammocrypta pellucida''. Another suggestion is to begin studies in cryopreservation. This could preserve [[gamete]]s and [[Glochidium|glochidia]], since it is challenging to induce natural reproduction.<ref name=":5" />

== Responsible parties == Kentucky Ecological Services Field Office, National Park Service, U.S. Forest Service, Indiana Department of Natural Resources, Tennessee Valley Authority, Tennessee Wildlife Resources Agency, Tennessee Department of Conservation, Fish and Wildlife Enhancement, Illinois Department of Conservation, Kentucky Department of Fish and Wildlife Resources, Kentucky State Nature Preserves Commission, Virginia Department of Game and Inland Fisheries, Kentucky Department for Surface Mining Reclamation and Enforcement, US Office of Surface Mining Reclamation and Enforcement, West Virginia Department of Natural Resources, USFWS Regional Office 5, USFWS Regional Office 3, USFWS Regional Office 4

==References== {{Reflist}}

[[Category:Molluscs of the United States]] [[Category:Obovaria|retusa]] [[Category:Bivalves described in 1819]] [[Category:Taxonomy articles created by Polbot]]