Prioritising the conservation of benthic, sedentary, and invertivorous fish species in the East China Sea: Insights from multidimensional rarity

Rare species are a crucial component of global biodiversity, contribute disproportionately to ecosystem functions and services, and represent a key target for conservation policies. Examining species rarity across multiple dimensions (taxonomic, functional, and phylogenetic) can offer deeper insights into biodiversity patterns. Using seven years of bottom trawl survey data, along with fish trait and mitochondrial gene information, this study quantified rarity indices for 242 fish species in the central East China Sea, including taxonomic, functional, and phylogenetic rarity, as well as species restrictedness. Differences in rarity among fish with different traits were assessed, and the relationships between the various rarity indices were explored using generalized additive models. Finally, taxonomically, functionally and phylogenetically rare species were identified. The results showed that the taxonomic, functional, and phylogenetic rarity of benthic species was significantly higher compared to benthopelagic and pelagic species. Sedentary species exhibited the highest levels of taxonomic, functional, and phylogenetic rarity, while mobile species showed the lowest levels of multidimensional rarity. Invertivorous species displayed higher taxonomic and functional rarity, as well as species restrictedness, compared to herbivorous-invertivorous and invertivorous-piscivorous species. Correlations between different rarity indices were very weak. A total of 34 taxonomically rare species, 18 functionally rare species, and 14 phylogenetically rare species were identified, with five species being rare across all three dimensions. Our findings emphasise that, in addition to prioritising taxonomically, functionally, and phylogenetically rare species in conservation, future coastal fish conservation and management efforts should also enhance protection for benthic, sedentary, and invertivorous species.