Canary Island Sea Urchin Populations Face Local Extinction Amid Global Pandemic

A widespread marine pandemic is causing severe depletion of sea urchin populations globally, with recent assessments confirming near-total collapse in several critical areas. The species *Diadema africanum*, vital to the Canary Islands' marine ecosystem, has been driven to the brink of local extinction following extensive mortality events documented throughout 2023 surveys.

Research led by Iván Cano, a doctoral student at the University of La Laguna, details the crisis, which began in early 2022 with die-offs observed off La Palma and La Gomera before spreading eastward across the archipelago. Visual censuses conducted across the seven main islands revealed drastic declines in adult densities of *D. africanum*; specifically, Tenerife saw a 99.66% drop and La Palma a 73.8% decrease when compared to 2021 figures, establishing the lowest recorded levels since monitoring commenced.

This localized catastrophe in the Canaries mirrors synchronous mass mortality incidents affecting various *Diadema* species across the Caribbean, the Mediterranean Sea, the Red Sea, and the Western Indian Ocean, prompting an international research team to classify the event as a worldwide pandemic. The 2022-2023 outbreak proved more destructive than previous events in 2008 and 2018 because the subsequent recruitment of juveniles and production of larvae have almost entirely ceased, indicating a profound disruption to the species' life cycle.

*Diadema* genus sea urchins function as essential ecosystem engineers by grazing on algae, thereby safeguarding vulnerable hard coral structures that require sunlight to survive. The documented loss of these grazers has correlated with a significant surge in algal cover and a subsequent decline in hard coral cover in affected zones. In the Caribbean, for example, this pattern has been observed where coral cover has reportedly halved while algal cover increased by 85%.

Tenerife experienced a population decrease reaching 99.7%, accompanied by a complete recruitment failure throughout 2023, with no larval settlers detected following the historical settlement peak. Oceanographic data suggest that anomalous high-energy southern swells and long-lasting eastward currents may have contributed to the initial outbreaks in La Gomera and La Palma. Researchers caution that without these crucial grazers, global rehabilitation efforts for already damaged coral reefs will face significant impediments, echoing the severe phase shift in the Caribbean following the 1983 die-off of *Diadema antillarum*.

While the primary threat is ecological, *D. africanum* in Tenerife have also been subject to other environmental studies; an assessment in 2022 examined microplastic content in 33 specimens, finding that ingested items were predominantly microfibers composed of cellulosic, polypropylene, and polyethylene terephthalate. A similar pathogen, a ciliate *Scuticociliate* parasite suspected in the Caribbean outbreaks, is also implicated in the current global die-off, raising concerns about potential spread to the Pacific Ocean.