Even though Congeria has long been thought to be a single pan-Dinaric species (Congeria kusceri Bole, 1962), phylogenetic analyses have recently clarified that it consists of three distinct species, namely Congeria kusceri Bole, 1962, Congeria mulaomerovici Morton and Bilandžija, 2013, and Congeria jalzici Morton and Bilandžija, 2013 (Bilandžija et al. 2013).

The genus Congeria is endemic to Europe and known from only 51 sites in the Dinaric karst (Bilandžija et al. 2022).

Global and European regional assessment: Endangered (EN)
EU 27 regional assessment: Endangered (EN)

The European endemic South Dinaric Cave Clam (Congeria kusceri) is assessed as Endangered (EN B1ab(ii,iii,v)) globally and for the EU 27 Member States as the species has a narrow distribution with an estimated extent of occurrence (EOO) of less than 5,000 km², it occurs in fewer than five threat-defined locations and the quality of its habitat is declining. Furthermore, there has been a significant decline in their populations after the channelisation of the River Trebišnjica in the 1960s, where populations from some caves completely disappeared. It is expected that the project "Upper Horizons" will cause a further significant decline in population size and habitat quality. The estimated area of occupancy was not considered for assessment as it is a very unreliable parameter for subterranean species, sensitive to the used calculation method and new findings.

Congeria kusceri inhabits subterranean habitats of the Neretva River basin in southern Herzegovina and Dalmatia (Croatia). Living specimens have been found in four sites in Croatia (Jasena ponor, Jama u Predolcu, Pukotina u Tunelu Polje Jezero–Peračko Blato, Šprljina jama) and eight in Bosnia and Herzegovina (Žira jama, Tihaljina, Gradnica, Doljašnica, Plitica, Buljovica, Kapuša estavela, Jama Perača) (Bilandžija et al. 2013, Bilandžija et al. 2022, SubBioDB 2022). Furthermore, shells of C. kusceri were found at an 24 additional sites, indicating that we cannot reach their main habitat or that it has been destroyed (Bilandžija et al. 2013, Bilandžija et al. 2022). The disappearance of populations has been documented in three caves (Meginja, Baba kod Strujići and Izvor-špilja kod kapelice Sv. Mihovila) (Bilandžija et al. 2021). The estimated EOO is around 883 km².

This species can reach high population densities. For example, the population in the cave Jama u Predolcu was estimated to be between 72,454 and 72,906 individuals (Jovanović Glavaš et al. 2017). There is evidence of significant decreases in the populations of Congeria kusceri. The disappearance of the subpopulation of the C. kusceri has been reported from caves Meginja and Baba kod Strujići, presumably after the channelisation of the Trebišnjica River in the 1960s. The disappearance from the cave Izvor-špilja kod kapelice Sv. Mihovila occurred more recently, after 1998. The subpopulation in Žira cave is conservatively estimated to have decreased by more than 99% following changes that affected the flow of Trebišnjica (Bilandžija et al. 2021). We expect that the Upper Horizons Hydropower plants that are in construction will cause further declines in population size.

Congeria kusceri inhabits subterranean aquatic habitats that are almost constantly underwater. The animals can survive some time outside water (in times of low waters) and probably in that time high air humidity is important (Bilandžija et al. 2014). The species lives in waters with temperatures of 7.2 to 19.4°C, attached to the stone surface and it can be found in larger groups (Bilandžija et al. 2014). These animals feed by filtrating small organic matter from the water. The species reproduces by releasing the sperm into the water, which is, in all probability, ‘inhaled’ by the females from the water. Embryogenesis and early development occur within the mother. Larvae or young adults are released through the birth canal (Morton and Puljas 2013). The estimated life span is more than 50 years (Puljas et al. 2014). The biotic interactions of this species are poorly known.

An important identified threat to this species is hydrotechnical engineering which leads to the degradation or loss of their habitat. After the channelisation of the River Trebišnjica in Popovo polje in the 1960s, the flooding regimes changed, the connectivity between surface and subterranean water was disturbed and the water table lowered. Nearly 500 sinkholes and caves in Popovo polje lost their annual water supply, causing populations of clam (Congeria kusceri) to die out (Lewarne 1999, Čučković 1983). The hydrological changes caused most of the springs on the right bank of Neretva River to dry out and caused the salinisation of water (Vranješ et al. 2013). Upper Horizons Hydropower plants that are in construction will significantly affect the water flow, including the divergence of water from Neretva to Trebišnjica catchment (Stojanović Bjelic et al. 2012, Čokorilo Ilić et al. 2016). This will cause further salinisation of water, which will have a large negative effect on the aquatic cave fauna.

One of the main threats to this species is increasing groundwater pollution. Many sites are threatened by the deterioration of water quality due to unsolved wastewater management, illegal dumps and agricultural effluents, which are especially problematic in lower Neretva valley and partly in Popovo Polje. Sites near main roads are threatened by run-off from roads and possible oil spills. In the area, many smaller springs and wells have been modified to serve as (additional) water supply, and irrigation systems have been set up, mostly draining water from the rivers. If overexploitation occurs, this could have a negative effect on Congeria kusceri. Any changes influencing groundwater will probably have an even more severe effect due to climate change affecting precipitation dynamics (Bilandžija et al. 2021). Furthermore, the building of new roads and urbanisation represents a threat to the species as it is related to increased pressure on groundwater and possible physical modifications of the habitat. For example, cave Jama u Predolcu is threatened to be physically degraded due to the construction of the new bypass road for Metković city and also due to intensive urbanisation. The modification of the cave entrance the spring cave Izvor-špilja kod kapelice Sv. Mihovila is suspected to be the cause of the disappearance of populations of C. kusceri (Bilandžija et al. 2021). The construction works in cave Jama u Predolcu, which includes widening of the entrance, could negatively impact the C. kusceri population living there.

This species is not utilised.

Congeria kusceri is listed in Annexes II and IV of the Habitat Directive (Directive 92/43/EEC) and several Natura 2000 sites are designated for this species in Croatia. The species is listed on Revised Annex I of Resolution 6 (1998) of the Bern Convention and is legally protected in Croatia, where it is listed on the national Red List as Critically Endangered (Official Gazette No. 144/2013 and 73/2016). The subterranean habitats and fauna are also protected by national law in Croatia and entity-level laws in Bosnia and Herzegovina (Official Gazette of FBIH, No. 66/13, Official Gazette of Republic Srpska, No. 20/14, Official Gazette of Republic Croatia, No. 80/13, 15/18 and 14/19). Monitoring guidelines for the species are prepared for Croatia (Bilandžija et al. 2014), but regular ongoing monitoring is not implemented. In Bosnia and Herzegovina, Popovo polje is included in Natura 2000 planning areas (Site code: BA8300062, Congeria kusceri is one of the qualification species) and planned Emerald Network (SiteCode: BA0000012, Congeria kusceri is not listed as one of the qualification species). However, as those are only proposed sites, they have no formal implications. The protected area Zaštićeni pejzaž Vjetrenica-Popovo Polje covers some parts where shells of Congeria kusceri were found.

Legal protection status in Bosnia and Herzegovina needs to be established. It is necessary to strengthen policies that would prevent damaging projects such as the construction of hydropower plants. Actions to reduce and prevent pollution should include the implementation of conservation policies and raising awareness through education. It is important to set up a monitoring scheme and monitor populations regularly, which will enable the assessment of the current conservation status of subpopulations. Additional support for research on species biology is important to adequately target necessary conservation actions. Those actions require the allocation of adequate funds and intervention by local authorities. Research on various aspects of its biology is needed, especially on ecology and genetics. It is important to understand the resilience potential of the species and develop good monitoring practices. This will enable the assessment of the current conservation status of populations. Because subterranean water connections in karst areas are very complex, research on the connectivity of populations, living up and downstream catchments is necessary, along with research on the impacts of threats (constructions and pollution) on the cave aquatic fauna downstream.