Macroalgae and mobile reef invertebrates face high extinction risk

Identification of threatened species in the marine environment is hindered by high access costs and difficulties collecting population trend and geographical distribution data. These challenges have resulted in a poor coverage of marine species among assessments for the IUCN Red List of Threatened Species, reducing the potential value of the Red List for guiding conservation action in marine systems, including rocky and coral reefs. To quantify knowledge gaps in reef species threat assessments, we assessed population trends for 626 common shallow reef species at 869 sites around Australia from 1992 to 2024 using time series data from standardised ecological monitoring programs. A total of 82 of 229 species (36 %) with declining populations had rates of decadal decline that would qualify them as threatened based on Red List criteria. Over a third (38 %, n = 31/82) of these provisionally threatened species are endemic to the study region (Australia), with 5 currently listed as Least Concern and 26 Not Evaluated. Temperate macroalgae (12 species) and mobile macro-invertebrates (23 species: 14 Echinoderms, 8 Gastropods, 1 Malacostracan) are over-represented among provisionally threatened species and under-represented on the Red List. Expansion of monitoring and reporting programs, and more timely risk assessments that lead to improved management strategies, are required to better accommodate threats affecting speciose marine taxa, with the ultimate goal to allow proactive management, thereby reducing extinction risk. • Decadal trends in 626 species show > 25 % declines in 96 marine species, few with IUCN Red List extinction risk assessment. • Endemic reef species were twice as likely to show trends that qualify them as threatened compared to non-endemic species. • Previous IUCN Red List conservation assessments of shallow-reef species show clear taxonomic bias. • Temperate species, particularly macroalgae and macro-invertebrate species, are underrepresented in IUCN Red List assessments. • Inadequate contemporary Red List coverage may hinder conservation management of species at highest extinction risk.