Systematics, distribution, biology, and conservation of freshwater mussels (Bivalvia: Unionida) in China

Freshwater mussels (Mollusca: Bivalvia: Unionida) have a broad global distribution on every continent except Antarctica. However, owing to human activities, the diversity of freshwater mussels is seriously globally threatened. China is an important global biodiversity hotspot for this fauna. This article comprehensively reviews the 99 currently recognized species in China, collating for the first time their systematics, distribution, life-history traits, habitat preferences, conservation status, and main threats to suggest future management actions. The review showed that the taxonomic status and species validity of many freshwater mussels are still not well resolved. The freshwater mussel diversity in the Yangtze River Basin is higher than that in other freshwater habitats in China. Life history characteristics and habitat preferences are poorly known for most species. Only half of the total number of species in China have been assessed for their conservation status. Among those assessed, around half of them are threatened with extinction with more than 10% being considered as Data Deficient. The key threats identified as potentially related to species declines are pollution, habitat loss and fragmentation, loss of access to host fishes and overharvesting of mussels or their host fishes. The review shows that there is a strong geographical bias in the amount of knowledge available for freshwater mussels, with most of the available data being concentrated in the middle and lower reaches of the Yangtze basin. Almost no data are available for these taxa north of the Yellow River basin and in the west and south-west regions of China. To make future conservation and management more effective we suggest that efforts should be concentrated on: (i) increasing the amount of research on basic ecological and life-history features, including growth, life-span, reproductive cycle, host fish identification and habitat requirements of each species; (ii) establishing the interspecific and intraspecific genetic diversity patterns of Chinese freshwater mussels, to clarify their taxonomy, systematics and phylogeny, and to understand the phylogeography and population structure of each species; and (iii) urgently establishing protected areas for fish and mussels in locations of high species richness, such as Poyang Lake and Dongting Lake, and also in regions with high levels of endemism or genetic uniqueness, such as Guangxi Province, Yunnan Province and Heilongjiang Province. In addition, the need for habitat restoration and the conservation of freshwater mussels has become urgent in China, and an integrated systematic conservation and management plan should be developed and effectively implemented.