The Portuguese Man O’ War’s blue, alien-like appearance may invite a closer look. But beware! Their long, trailing tentacles pack a painful and sometimes dangerous sting. Often, they wash ashore, tempting curious kids to poke them with sticks. Other times, they float just beneath the surface, prompting surfers to stay alert for the jellyfish-like creatures.
But these notorious drifters aren’t all the same. A new study published in Current Biology by scientists from Yale University, the University of New South Wales (UNSW), and Griffith University in Australia reveals that the Man O’ War found off of Florida’s coast isn’t the same as the ones seen off eastern Australia.
While oceans are connected and many marine species have global ranges, the Portuguese Man O’ War (often called “bluebottles”) has adapted to different regions. Recognizing these distinctions could help us better predict their presence and protect people from their venomous sting.
Bluebottles in the Sea
What looks like a serene, single jellyfish floating in the vastness of the sea is actually a colony of specialized individuals called polyps. Belonging to the siphonophore order and known taxonomically as Physalia, these polyps work together as one unit.
Their balloon-like float keeps them at the surface, drifting with the wind using a small sail. This shape inspired their names: “bluebottle” for the float’s bottle-like appearance, and “Portuguese Man O’ War” for its resemblance to an old warship. Below the surface hide tentacles that can stretch up to 100 feet, filled with venom, trapping and paralyzing small fish, and occasionally harming humans.
Man O’ Wars are found in the Atlantic, Pacific, and Indian Oceans. In areas where they’re common, locals know to steer clear. Contact with their tentacles can cause intense pain, allergic reactions, and in rare cases, even death. That’s why researchers at UNSW set out to study their genetics, helping to prevent human encounters.
Read More: This Predatory Jellyfish Lived Before Plants Had Even Evolved
Merging Genetics and Citizen Science
The team sequenced the genomes of 151 Physalia samples and compared them with thousands of images submitted by citizen scientists on iNaturalist.org. The result: four genetically distinct species — Physalia physalis, P. utriculus, P. megalista, and P. minuta.
“We assumed they were all the same species,” said study co-author and Griffith University professor Kylie Pitt in a press release. “But the genetic data clearly show they’re not only different, they’re not even interbreeding despite overlapping ranges. The bluebottle is uniquely suited to long-distance travel, using its gas-filled float and muscular crest to catch the wind and sail the sea surface.”
These differences had been proposed as far back as the 18th and 19th centuries based on appearance, but only now has modern genetic analysis confirmed it.
Why Did Bluebottles Split Into Separate Species?
Despite living in the vast and connected open ocean, bluebottles have evolved into genetically distinct groups. “There’s this idea the open ocean is all connected ... and they’re all globally connected because they drift with the wind and the current,” added Pitt in the news release. “But that’s absolutely not the case.”
Using ocean circulation models, researchers showed that these populations align with major wind and current systems. Even though they travel well, thanks to their gas-filled floats and wind-catching crests, there are still barriers that limit interbreeding.
What’s especially intriguing is that multiple species coexist off eastern Australia. “What was the selection pressure that led to the differentiation?” Pitt noted. Answering that could reshape how we understand biodiversity in the open sea.
This research was supported by a 2022 Australian Research Council Linkage grant awarded to UNSW for the project Bluebottle Dynamics. The goal? To develop a forecasting tool together with Surf Life Saving Australia, the Bureau of Meteorology, and others, to help predict and prevent painful bluebottle stings.
Read More: Venomous Snot Helps These Jellyfish Stings Without Their Tentacles
Article Sources
Our writers at Discovermagazine.com use peer-reviewed studies and high-quality sources for our articles, and our editors review for scientific accuracy and editorial standards. Review the sources used below for this article:
Current Biology: Population genomics of a sailing siphonophore reveals genetic structure in the open ocean
National Oceanic and Atmospheric Administration: What is a Portuguese Man o’ War?
Having worked as a biomedical research assistant in labs across three countries, Jenny excels at translating complex scientific concepts – ranging from medical breakthroughs and pharmacological discoveries to the latest in nutrition – into engaging, accessible content. Her interests extend to topics such as human evolution, psychology, and quirky animal stories. When she’s not immersed in a popular science book, you’ll find her catching waves or cruising around Vancouver Island on her longboard.
