Scientists were shocked to find that bluebottles are not one species

Bluebottles – also known as Portuguese man o’ war – are jellyfish-like marine creatures with long, stinging tentacles that often wash up on beaches. It’s been widely assumed that bluebottles all belong to a single species, but a new global genetic survey has revealed otherwise.

Dr. Samuel H. Church of Yale University coordinated the genome work with Australian colleagues, including Professor Kylie Pitt from Griffith University. Their findings overturn two centuries of scientific classification.

Four species of bluebottles

The team sorted the specimens into Physalia physalis, P. utriculus, P. megalista, and a newly named Physalia minuta, the last discovered in waters south of New Zealand. Each species carries distinctive sail colors and float shapes – traits once dismissed as harmless variation.

Genetic markers show the four lineages do not interbreed, even when they occupy the same stretch of ocean. This pattern means evolution is at work in the open sea, not only along coastlines or around islands.

“We were shocked, because we assumed they were all the same species,” said Professor Pitt. Her remark echoes a long‑held textbook view now overturned.

Every colony is a siphonophore – a floating commune of genetically identical zooids that act as one animal. The arrangement lets a bluebottle grow long feeding tentacles while the gas‑filled float keeps the colony at the surface, a lifestyle that defines the neuston layer.

Differences go beyond appearance

Raw genomes alone rarely hint at an animal’s appearance, so the researchers combed through 4,000 beach photographs. Color signatures and sail angles in the pictures matched the genetic lineages one by one.

Citizen scientists had, in effect, been taking field notes for years without knowing it. Their uploads supplied location data that helped map where each species turns up during different wind seasons.

Machine‑learning tools flagged subtle differences, such as a deep‑purple crest on P. megalista or the small, clear float on P. minuta. Laboratory vouchers later verified those traits under a microscope.

The public photo trove also clarified left‑handed versus right‑handed sails, a feature that decides which way a bluebottle is blown. Such handedness now appears tied to species identity rather than simple developmental chance.

Ocean currents separate bluebottle species

Ocean circulation models recreated likely drift paths from hatchling to adult, revealing corridors that keep populations apart. Prevailing winds in the Pacific sweep P. utriculus west toward Australia, while the South Equatorial Current loops P. megalista into the Atlantic. 

The new species, P. minuta, hugs eddies of the Tasman Front, a route that spirals larvae southward before they ever cross open ocean. Because gonads detach and sink below the surface to spawn, deep water layers also partition gene flow.

Subtle climate shifts could shuffle these corridors and mix the species in the future, but for now the lines stay crisp. That stability gives evolutionary forces room to sculpt body size, venom genes, and reproductive timing without interference.

The finding challenges a common idea that wind‑powered drifters form one gigantic, well‑mixed population. Instead, even a creature built for travel can remain genetically provincial.

Bluebottle stings vary by species

Surf Life Saving Australia ranks bluebottle contact as a leading reason for first‑aid calls, spurring a research grant to build a beach sting forecast.

Knowing which species is likely to arrive could sharpen those alerts, because tentacle length and venom chemistry differ among the four.

During the summer of 2017, more than 38,000 people were treated for bluebottle stings in Queensland alone – a spike of 900 percent over the prior season.

Forecasting bluebottle seasons

Public health planners can now add species identity to their toolbox instead of relying on wind direction alone.

Lighter winds often carry the smaller P. minuta onto sheltered south‑facing bays, where novice swimmers gather.

Lifeguards armed with species‑level forecasts might adjust patrols or signage accordingly. Thermal anomalies that favor jellyfish blooms may not boost every bluebottle equally, given their genetic split.

Future sting seasons could therefore hinge on which lineage catches the breeze rather than on sheer water temperature.

Hidden population structure in the ocean

The bluebottle story joins other case studies of copepods and pteropods that show hidden population structure in the high seas.

Collectively, these results overturn the old axiom that “everything is everywhere” once an organism can drift. Marine cleanup projects often claim surface life is sparse, implying little ecological risk when skimming plastics.

Evidence of partitioned diversity urges far more caution before nets sweep across convergence zones.

Broader implications of the research

Pharmaceutical scouts have isolated novel peptide toxins from P. physalis, but untapped species may hold different compounds with medical promise. A four‑species framework sets a clearer path for bioprospecting teams. 

Climate models aiming to forecast oceanic carbon cycling need accurate species counts because each colony’s buoyant gas is nearly 13 percent carbon monoxide. Four distinct production rates could alter estimates of gas exchange at the air–sea interface.

Researchers who track long‑range migrants, from sea turtles to seabirds, can now refine diet studies. Predator scat may tell which bluebottle species dominates a given flyway, adding another layer to ecosystem maps.

Toxin genes in bluebottle species

Work is already under way to test whether the four lineages differ in toxin genes, an angle that could explain regional differences in sting severity.

Another puzzle lies in the handedness trait, which might be hardwired by alleles rather than molded by early winds.

Field biologists plan to tag floats with tiny temperature loggers to see how much time each species spends in sun‑baked surface water. Results should reveal whether thermal tolerance helped split the lineages in the first place.

The study is published in the journal Current Biology.

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