Sea urchins across Canary Islands and Madeira are collapsing, with Diadema africanum populations falling by up to 99.7% between 2022 and 2023. Scientists fear a global pathogen may be causing it. Researchers said while they don't yet know which pathogen is causing these die-offs, mass mortality events in world have earlier been linked to single-celled parasitic organisms, scuticociliate ciliates.