A bit more on the Portuguese Man O’ Wars this past week

Posted By on February 18, 2023


Brenda commented that I didn’t link any information on the the large numbers of Portuguese Man O’ Wars earlier this week, so figured I would share a beach photo of a bourgeoning Portuguese Man O’ War spawn that were washing up all over the beach this past week (click above). The interesting colored spot on the shore has me linking and reading a bit more … and finding this “lefthanded vs righthandedness” section intriguing.

For each man o’ war or bluebottle, the float can be oriented towards the left or the right (dimorphism), believed to be an adaptation that prevents the entire population from being washed on shore to die.

The “left-handed” bluebottles sail to the right of the wind, while the “right-handed” bluebottles sail to the left. The wind will always push the two types of bluebottles in different directions, so at most half the population will be pushed towards the coast.

Regional populations of Portuguese man o’ war can have substantial differences in float size and the number of long tentacles used for hunting. The regional form previously known as P. utriculus, the bluebottle, has a float rarely exceeding 10 cm in length and has one long hunting tentacle that is less than 3 m long. In comparison, the typical man o’ war has a float of around 15 cm, reported up to 30 cm, and several hunting tentacles that can reach 30 m in mature colonies when fully extended.

A Portuguese man o’ war is somewhat asymmetrically shaped: the zooids of the colony hang down not quite from the midline of the pneumatophore, but offset to either the right or left side of the midline. When combined with the trailing action of the tentacles (which function as a sea anchor), this left- or right-handedness makes the colony sail sideways relative to the wind, by about 45° in either direction. Colony handedness has therefore been theorized to affect man o’ war migration, with left-handed or right-handed colonies potentially being more likely to drift down particular respective sea routes. While previously believed to develop as a result of what winds a colony experienced, handedness in fact emerges early in the colony’s life, while it is still living below the surface of the sea.


Photo from mid-February 2023 that I really liked and wanted to include


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