The blue dragon: The spectacular sea slug behind beach closures in Spain

https://english.elpais.com/climate/2025-08-26/the-blue-dragon-the-spectacular-sea-slug-behind-beach-closures-in-spain.html

The blue dragon: The spectacular sea slug behind beach closures in Spain
This summer, it was sighted in Cadiz, Valencia, Alicante, and Lanzarote. Its sting can cause skin irritations similar to those of a jellyfish

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The blue dragon, the small sea slug that forced beach closures in Spain (Spanish audio)
Blue dragon ('Glaucus atlanticus') specimen collected in the Bay of Algeciras. Courtesy image.

ESTHER SÁNCHEZ
Madrid - AUG 26, 2025 - 10:47 EDT

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The species lives on the ocean surface, drifting with the currents. “They float upside down, like when we float on our backs, to camouflage themselves with the sea’s blue color, and on their underside they are white, blending with sunlight when seen from below. It’s a defensive strategy,” he says. This feature distinguishes the blue dragon from other sea slugs, which stay in the intertidal zone or at greater depths. On the Iberian Peninsula, around 300 species have been described, and new ones are still being discovered.

The blue dragon roams the waters of the North and South Atlantic and the Pacific in temperate waters, but sightings in the Mediterranean, as is now happening, are rarer. “The species was cited [in a scientific publication] in the second decade of the 20th century in the Balearic Islands, although the first record was in 1839 in the Canary Islands, but then a long time passed before it was detected again,” Cervera notes. This is in contrast to the Portuguese man-of-war, which has a wider distribution in the Mediterranean.

The arrival of these specimens has been linked to rising Mediterranean temperatures, which at the end of June exceeded 28ºC (82ºF), with thermal anomalies of five degrees. The researcher stresses that there is still not enough evidence to confirm this link, since studies are lacking on the species’ ecology and the most favorable environmental conditions for it. “What would be very interesting is to carry out monitoring, and whenever someone sees a specimen, they should take a photo and send it to us so we can keep a record,” he suggests.

… video at link if someone can post it? Tia…