Sea Change

In February 2022, Cano and colleagues first observed widespread die-offs of D. africanum near La Palma and Gomera in the western Canary Islands. Over the next few months, the outbreak spread eastward across the archipelago. Infected urchins exhibited unusual behaviors—they became sluggish, moved oddly, stopped reacting to stimuli, and eventually lost both flesh and spines before dying.

Figure 1. Sea Urchin Numbers Crash Worldwide, Cause Still Unknown

The researchers recognized these signs, as this was not the first mass mortality event in the region. Similar outbreaks occurred in early 2008 and again in early 2018, killing roughly 93% of D. africanum on Tenerife and La Palma, as well as around 90% of populations in the nearby Madeira archipelago. Figure 1 shows Sea Urchin Numbers Crash Worldwide, Cause Still Unknown.

But the 2022 outbreak was different. Unlike the 2008 event, when many affected populations recovered—sometimes surprisingly quickly—the 2022 die-off showed no such rebound. Instead, a second wave of mass mortality swept across the Canary Islands throughout 2023.

To gauge the scale of the impact, Cano and colleagues surveyed D. africanum at 76 sites across the seven main islands from summer 2022 to summer 2025, comparing these findings with historical records. They also enlisted professional divers to report on urchin abundance at their regular dive sites between 2018 and 2023. In addition, dispersing larvae were collected using traps at four locations off eastern Tenerife in September 2023, coinciding with the peak of the spawning season, and the number of newly settled juveniles was recorded at the same sites in January 2024.

“Our analyses show that D. africanum populations across the Canary Islands are at an all-time low, with several sites approaching local extinction,” Cano said.

“Furthermore, the 2022–2023 mass mortality event impacted the species across the entire archipelago. For instance, since 2021, populations have declined by 74% on La Palma and an astonishing 99.7% on Tenerife.”

Prickly issue

The team also found that effective reproduction has largely ceased on Tenerife’s eastern coast: traps caught only negligible numbers of larvae, and no early juveniles were observed in surveyed shallow rocky habitats.

“Reports from other regions suggest that the 2022–2023 die-off may be part of a wider marine pandemic, with serious consequences for these critical reef grazers,” Cano concluded.

“The exact pathogen behind these die-offs remains unknown,” Cano explained. “Mass mortality events in Diadema elsewhere have been linked to scuticociliate ciliates of the genus Philaster, a type of single-celled parasite.”

“Previous Canary Islands die-offs were associated with amoebae like Neoparamoeba branchiphila, often following periods of unusually strong southern swells, similar to the conditions in 2022. Without a confirmed identification, we can’t say whether the agent arrived via currents or shipping from the Caribbean, or if climate change played a role.”

“At this point, it’s unclear how this marine pandemic will evolve. Fortunately, other Diadema populations in Southeast Asia and Australia appear unaffected—but we cannot rule out future outbreaks or further spread.”

Source: SciTECHDaily

Cite this article:

Janani R (2025), Global Sea Urchin Populations are Plummeting, Mystery Persists Over the Cause, AnaTechMaz, pp. 637