Co-extinctions are increasingly recognized as one of the major processes leading to
the global biodiversity crisis, but there is still limited scientific evidence on the magnitude of potential impacts and causal mechanisms responsible for the decline of affiliate (dependent) species. Freshwater mussels (Bivalvia, Unionida), one of the most
threatened faunal groups on Earth, need to pass through a parasitic larval (glochidia)
phase using fishes as hosts to complete their life cycle. Here, we provide a synthesis
of published evidence on the fish–mussel relationship to explore possible patterns in
co-extinction risk and discuss the main threats affecting this interaction. We retrieved
205 publications until December 2015, most of which were performed in North
America, completed under laboratory conditions and were aimed at characterizing the
life cycle and/or determining the suitable fish hosts for freshwater mussels. Mussel
species were reported to infest between one and 53 fish species, with some fish families (e.g., Cyprinidae and Percidae) being used more often as hosts than others. No
relationship was found between the breadth of host use and the extinction risk of
freshwater mussels. Very few studies focused on threats affecting the fish–mussel
relationship, a knowledge gap that may impair the application of future conservation
measures. Here, we identify a variety of threats that may negatively affect fish species,
document and discuss the concomitant impacts on freshwater mussels, and suggest
directions for future studies.The Portuguese Foundation for Science and Technology—FCT through POPH/FSE funds supported VM, MI and MLL under grants (SFRH/BD/108298/2015), (SFRH/BPD/90088/2012), (SFRH/BD/115728/2016), respectively. KD acknowledges the support from the Czech Science Foundation (13-05872S). RS acknowledges the support of the strategic programme UID/BIA/04050/2013 (POCI-01-0145-
FEDER-007569) funded by national funds through the FCT I.P. and by the ERDF through the COMPETE2020-Programa Operacional Competitividade e Internacionalização (POCI). This study was conducted as part of the project FRESHCO: Multiple implications of invasive species on Freshwater Mussel co-extinction processes,
supported by FCT (contract: PTDC/AGRFOR/1627/2014)
