A mysterious disease is driving a global collapse of Diadema sea urchins, with the Canary Islands experiencing particularly severe declines. Without these crucial grazers, entire reef ecosystems may be pushed into dangerous imbalance. Credit: Shutterstock Sea urchins play a crucial role in the ocean, acting as ecosystem engineers much like large grazers on land. As they feed on seaweed and seagrass, they trim back algae and help protect slow-growing species such as corals and certain calcifying