Global patterns of elasmobranch diversity and consequences of species loss

Elasmobranchs (sharks and rays) are among the most threatened marine vertebrates worldwide, yet the consequences of their decline across multiple dimensions of biodiversity remain poorly understood. Here, we investigated global patterns of taxonomic, functional, and phylogenetic diversity of marine elasmobranchs across the 18 FAO Major Fishing Areas and evaluated the consequences of sequential species loss based on IUCN threat categories. Species occurrence, ecological traits, phylogenetic relationships, and fisheries catch data were compiled from global databases to quantify biodiversity patterns and simulate extinction scenarios. Regions with higher chondrichthyan catches consistently exhibited greater species richness, functional diversity, and phylogenetic diversity, reflecting shared large-scale environmental and biogeographic drivers rather than direct effects of fishing activity. Threatened species displayed significantly greater Functional Uniqueness and Evolutionary Distinctiveness than non-threatened species, indicating that extinction risk is concentrated among ecologically and evolutionarily unique taxa. Accordingly, simulated extinctions based on IUCN categories produced significantly greater biodiversity losses than equivalent random species removals, demonstrating that extinction risk is strongly non-random. Observed extinction sequences consistently produced significantly greater biodiversity losses than random species removals, reducing species richness by up to 42.8%, functional diversity by 35.9%, and phylogenetic diversity by 34.2% under the most severe scenario. Our findings demonstrate that the loss of threatened elasmobranchs disproportionately erodes ecosystem functioning and evolutionary history beyond that expected from species richness decline alone. Integrating taxonomic, functional, and phylogenetic perspectives therefore provides a more comprehensive basis for identifying global conservation priorities and managing marine biodiversity under increasing extinction risk.