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Facts about the Portuguese Man O' War

[Phylum: Cnidaria] [Class: Hydrozoa] [Order: Siphonophorae] [Family: Physaliidae (monotypic)]

The jelly-like Portuguese men of war (also called bluebottle) are commonly known for their oceanic floating habits and powerful sting. Yet, they are frequently mistaken as being jellyfish.

This guide contains fun and interesting facts about the Portuguese man-of-war (Physalia physalis) species and why these hydrozoans are feared by swimmers and scuba divers.

Portuguese Men-of-War are Not Jellyfishes

It's easy to see why many people think these creatures belong with the Class: Scyphozoa (jellyfish species).

However, the Portuguese man-of-war are Siphonophora - meaning they are a class of hydrozoans.

Here's the thing:

They certainly look like sea jellies. But, they are actually related closer to stinging hydroids and fire coral.

The blue gas-filled bladder and long flowing tentacles help Portuguese man-of-war float freely with ocean currents. But, making contact with the venomous tendrils of these cnidarians can cause intense pain and other symptoms that may affect the whole body.

Pro Tip: Click through to the diving injuries section for information about Portuguese man-of-war sting symptoms and treatment (e.g. applying white household vinegar to stabilise unfired nematocysts).

Where Do Portuguese Man O' War Live?

The genus contains two species. Physalia physalis (Portuguese man-of-war) prefers the cold waters of the Atlantic Ocean. The other species, Physalia utriculus (bluebottle) inhabits the warmer waters of the Indo-West Pacific.

In fact, the Gulf Stream of the northern Atlantic, and the tropical and subtropical regions of the Indian and Pacific, are other oceans where the population is expanding.

Here's the thing:

These regions are seeing warming ocean temperatures combined with a decrease in oxygenated water. As a result, reports of man of war sightings in Canada and Scotland are becoming commonplace.

Man of War Characteristics and Behaviour

The appearance and characteristics of Portuguese men-of-war are somewhat deceiving. To the untrained eye, the organism might look like it's a single creature. But in fact, it is a colony made up of four different types of polyps (called zooids).

This pleustonic species floats at the surface of almost all oceans (excluding the smallest and shallowest - the Arctic Ocean). Hence, the colony relies on the wind and ocean currents for movement.

In fact, a key difference between the Portuguese man-of-war and jellyfish is that they are unable to move on their own. Whereas, the makeup of jellyfish anatomy means they are able to create independent movement.

Interactions of Man O' War with Divers

Portuguese man-of-war stings rank among the common scuba diving injuries, along with the most frequent of all, barotraumas.

Their cnidocytes deliver a potent proteic neurotoxin, which can easily paralyse small fishes. Most of the stings from Physalia occur at the surface or on the beaches.

In case you were wondering:

The sting site may swell and you may see red slashes or welts. Besides suffering moderate to severe pain for a few days, other common symptoms of Portuguese man o' war sting include burning pain, fever, malaise, and red welts on the skin.

Pro Tip: The most likely place to encounter the submerged tentacles of cnidarians is the final three metres before you reach the surface. So, scuba divers and free divers should always look up and check around before surfacing.

What Do Portuguese Men-of-War Eat?

Physalia physalis are typical examples of marine invertebrates that are also carnivores. The float (gas bladder) can measure thirty (30) centimetres long (12 inches) and be thirteen (13) centimetres wide (5 inches).

But, don't be surprised to see long, flowing tentacles dangling up to fifty (50) metres (165 feet) below the surface.

Portuguese Man-of-War Sting Symptoms and Treatment.It uses the venom-filled stingers to paralyse and capture its prey, such as:

Portuguese Man-Of-War Reproduction

In fact, the individual colonies of polyps can only be entirely male or entirely female.

As a result, they will use a reproductive process known as 'broadcast spawning' (e.g. sexual reproduction).

When groups of females release their eggs, usually when the Autumn arrives, the males will respond by releasing their sperm 'simultaneously'. Thus, fertilisation takes place close in the water column close to the surface.

Threats and Natural Predators

Despite being a venomous open ocean predator, the estimated life span of the Portuguese man-of-war is only one (1) year.

There are only a few predators that will eat siphonophores (stinging, gelatinous invertebrates). But, the ones that prey on the man o' war species the most are loggerhead sea turtles (Caretta caretta), octopi, and Mola Mola (the ocean sunfish).

Pro Tip: It's thought that the common clown fish (Amphiprion ocellaris) may have limited immunity to the man of war's stings. This would explain how they can feed among its poisonous tentacles.

Fun Facts about Portuguese Man-of-War

  • Barring the Arctic Ocean, Physalia physalis exist in every ocean and they often float together in large colonies. In fact, groups of up to one thousand are commonplace.
  • Portuguese men-of-war are not commercially valuable and they have relatively few predators in the wild.
  • The Portuguese man-of-war can deflate its pneumatophore (floating bladder partially filled with carbon monoxide) to escape its predators by submerging below the surface. The same process helps to keep them from drying out on hot sunny days.
  • The holoplanktonic violet sea-snail (Janthina janthina) is a marine gastropod that preys on Portuguese men-of-war, using a bubble raft to float upside down and wait at the surface. The blue Glaucus sea slug employs the strategy, but they also repurpose the stinging cells to use to defend themselves against their predators.
  • Even if the colony dies, severed tentacles can still fire nematocysts and sting humans, even when they are floating in the water or they get washed up on the beach.
  • Nematocysts have two sizes, the smallest being 11 nanometres and the biggest is 24 nanometres. One (1) nanometre measures the same as one-billionth of a metre.
  • The Portuguese man-of-war species get their peculiar name from the similarity of their bladder shape to that of an old, wooden warship at full sail floating on top of the water.
  • A small creature, called the man-of-war fish (Nomeus gronovii), lives among the Portuguese man-of-war's venomous tentacles. Even though the fish is small, around eight (8) centimetres long (3 inches), it has no natural immunity against the stinging venom.

Related Information and Help Guides

Note: The short video [2:53 seconds] presented by Deep Marine Scenes contains stunning footage of the Portuguese man of war (bluebottle).

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