Japanese scientists discover a new species of venomous 'Portuguese man-of-war'

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It should never have appeared in Japan. And yet, during the summer of 2024, a venomous sea creature with hypnotic colours and an astonishing history appeared on the beaches of northern Japan. This is how researchers discovered Physalia mikazuki, a new species similar to the physalia, probably transported by exceptionally warm ocean currents.

While the discovery is fascinating, it also sends out an alarming signal about the health of our oceans.

Gamo beach, in Sendai Bay, is not a place that 'tropical visitors' visit regularly. Its historically temperate waters have always created a natural frontier for species typical of warmer seas. So when, in July 2024, some locals identified strange deep-blue floating structures along the coastline, the attention of scientists was immediately drawn.

For years, scientists believed that the Physalia genus comprised just one species, or two at most. However, analysis of the specimens washed up on the coast of the Tohoku region revealed a different reality: a new species had just appeared in broad daylight.

A new species for science

Yoshiki Ochiai, who was working on a completely different research project in Sendai Bay, came across the organism in question which had never been seen in temperate waters. He collected it, transported it to the laboratory and began a long and painstaking process of observation, comparison and analysis of its anatomical details.

The name chosen, Physalia mikazuki, has a special meaning: in Japanese, 'mikazuki' means 'crescent moon' and recalls the shape of the helmet worn by the legendary samurai Date Masamune, who also founded the town of Sendai. A symbolic link with the region where the species was first seen.

From a purely physical point of view, the differences are far from minor. The size of this new Portuguese man-of-war is much smaller than those we already know of: its float measures between 9 and 72 millimetres, whereas for the better-known species it can reach 30 centimetres. Its colours are intense, including shades ranging from deep blue to violet, with a translucent blue-green membrane running through.

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A worrying arrival

Like all physalies, Physalia mikazuki is not a true jellyfish. It's a siphonophore, i.e. a colony of organisms that cooperate as if they were a single living being. While some float thanks to a gas-filled bladder, others capture prey, others defend the colony and others digest and reproduce. A perfectly tuned biological machine, but extremely dangerous.

Its presence in Japan is not just a scientific curiosity. Researchers have also been able to reconstruct the path  these organisms went through using digital simulations of ocean currents. They were able to demonstrate that abnormal marine heat waves and warmer-than-usual currents had transported the tropical species further north.

The consequences of this change are not negligible. From an ecological point of view, Physalia mikazuki feeds on small planktonic organisms and fish larvae, with the risk of upsetting local balances and having an impact on fishing activities. For humans, the danger is real: getting stung by Physalia mikazuki is painful and potentially dangerous.

This discovery, published in the scientific journal Frontiers in Marine Science, is concrete proof that the ocean is changing, bringing with it species and problems that until recently seemed very far apart.

Source: Frontiers in Marine Science

(©GreenMe.it/Managing Editor: Selma Keshkire - The Press Junction/Picture: Unsplash)