Host‐specificity of the endangered thick‐shelled river mussel (Unio crassus, Philipsson 1788) and implications for conservation

Abstract

ABSTRACT1. The complex life cycle of the endangered thick-shelled river mussel (Unio crassus, Philipsson 1788) includes an obligatory parasitic phase on a host fish. Consequently, knowledge of the interaction of U. crassus with its host species is crucial for the development of effective conservation strategies.2. The objective of this study was to assess systematically the host suitability of eight different fish species, including six native species which naturally co-occur with U. crassus, as well as two non-native species. All tested fish species were successfully infected with glochidia of U. crassus, which were present on their gills 2 days after exposure.3. Phoxinus phoxinus and Squalius cephalus were the most suitable hosts as indicated by both the highest total glochidial load and the highest fish-weight-normalized glochidial load after 16 days and 48 days. Salmo trutta, Alburnoides bipunctatus and Cottus gobio were less suitable, losing~90% of glochidia within 16 days. Alburnus alburnus, invasive Neogobius melanostomus and introduced Oncorhynchus mykiss lost more than 98% of glochidia within 16 days, indicating they are unsuitable hosts.4. U. crassus larvae did not grow significantly (<15%) during their metamorphosis on suitable hosts, suggesting that the most obvious advantage of the host-dependent phase in the U. crassus life cycle is the dispersal by fish vectors. The observed differences in the developmental speed and the timing of excystment on different suitable host species are likely to increase the chances of successful dispersal and survival in adverse environmental conditions. 5. The sustainable conservation management of U. crassus populations is closely linked to the effective management of their host fish populations. In particular, the currently underestimated ecological functions of low-valued fish species such as S. cephalus and P. phoxinus clearly deserve better consideration in the conservation management of U. crassus habitats and stream ecosystems.

Host specificity and metamorphosis of the glochidium of the freshwater mussel Unio tumidiformis (Bivalvia: Unionidae)

“…Previous studies on European Unio species supported this statement (Berrie and Boize 1985, Araujo et al 2005, Blažek and gelnar 2006, taeubert et al 2012a. Experimental infections with Unio crassus Philipsson, 1788 and Unio mancus lamarck, 1819 revealed that their glochidia can metamorphose successfully on a broad range of fish species from different genera (Hochwald and Bauer 1990, Araujo et al 2005, taeubert et al 2012a. However, glochidia from both species were found only in a restricted number of fish species in the wild (Engel and Wächtler 1989, Hochwald and Bauer 1990, Araujo et al 2005, taeubert et al 2012b, suggesting a more ecologically driven specific host-parasite relationship.…”

“…disCUssion Freshwater mussels belonging to the subfamily Unioninae sensu graf and cummings (2006) are known to present a generalist host-parasite relationship (Watters and o'dee 1998). Previous studies on European Unio species supported this statement (Berrie and Boize 1985, Araujo et al 2005, Blažek and gelnar 2006, taeubert et al 2012a. Experimental infections with Unio crassus Philipsson, 1788 and Unio mancus lamarck, 1819 revealed that their glochidia can metamorphose successfully on a broad range of fish species from different genera (Hochwald and Bauer 1990, Araujo et al 2005, taeubert et al 2012a.…”

“…the host specificity of the glochidia and their preferred site of attachment significantly vary between species. some species are known to parasitize only a few fish species, whereas others exploit a wide range of potential hosts (lefevre and curtis 1912, Berrie and Boize 1985, Haag and Warren Jr. 1997, Araujo et al 2001, Blažek and gelnar 2006, taeubert et al 2012a. glochidia equipped with hooks mainly encapsulate on the fish fins and body surface of many host species.…”

A spatially explicit approach to prioritize protection areas for endangered freshwater mussels

“…Both species are therefore currently listed as Endangered on the IUCN Red List (IUCN, ) and protected under EU law (Annex II and Annex IV of the EU Habitats Directive for U. crassus ; Annex II and Annex V for M. margaritifera ). Despite their shared conservation status, these species differ substantially in their habitat requirements (Denic, Stoeckl, Gum, & Geist, ; Geist & Auerswald, ) and host use (Taeubert & Geist, ; Taeubert, Gum, & Geist, ). Margaritifera margaritifera is often considered as a habitat specialist.…”

Influence of host fish age on a mussel parasite differs among rivers: Implications for conservation

“…A juvenile mussel's size also has an impact on recruitment, where a large juvenile has a higher chance of survival compared to a smaller sized mussel. One factor that regulates the condition and abundance of hatched juveniles is the host fish species (Arvidsson et al, 2012;Taeubert et al, 2012). Another factor that impacts the number of hatched juveniles may be the age of the host fish.…”