Seaweed Flourishes as Diadem Sea Urchins Vanish

The diadem sea urchin, once a common sight in the seas around Lanzarote, is now almost impossible to find.

The long-spined urchin was once regarded as a plague around the island’s coasts, and was blamed for the “desertification” of marine ecosystems, stripping algae and seaweed from rocks. Fruitless efforts were made to control the population of the urchins in 2005 and 2019.

However, it now appears that a global disease has almost wiped out the urchins. A report printed last winter estimated that 93% of urchins in the western Canaries had disappeared. Examples of other species of urchins can still be spotted around Lanzarote by divers and snorkellers, but the diadem is almost nowhere to be seen.

The disappearance of the urchins could be a factor in the large amounts of seaweed that can now be seen on various sea-beds around the island. Rocks and reefs that were previously stripped by urchins are now covered with seaweed, much of which washes up on shore.