The Portuguese Man o' War Predator/Prey Interactions

After looking at the positive interactions of Physalia physalis with different species in the sea, we can take a closer peek at their predatory and prey-like behaviors with various ocean-life.

The Portuguese man o’ war would be considered a mesopredator within the ocean, feeding on mostly small fish and fish larvae. Much of the Portuguese man o’ war’s predatory behavior is passive since its main weapons are the extended tentacular palpons, flowing with the currents in the waters below and waiting for prey to come into contact. Though they do not seek out prey actively, as soon as the tentacle senses the touch of a fish or larvae, it activates to a terrifying result. On the surface of the tentacles, thousands of equipped nematocyst batteries work quickly to penetrate soft-bodied organisms’ muscles and paralyze them with toxins. This toxin affects the neurological and respiratory centers, and in high doses it is quickly lethal. After envenomation, the prey is drawn up by the tentacle’s muscular structure, and the gastrozooids work to consume the newly acquired sustenance. According to a study done on Physalia physalis predation, the average rate of consumption by the siphonophore can come close to 120 fish larvae a day.

An illustration of a Portuguese Man o' War preying on a fish

When looking at their population cycles and the effect on prey populations, the Portuguese man o’ war undergoes long and large oscillations in all areas of their habitat. A typical period of the cycle is 20-years, per a study done in 2013, and the amount of all Cnidarians is increasing across the world. These oscillations can lead to blooms, which are substantial increases in the population size within a short time period due to higher reproduction rates. Blooms result in higher population density as well, which affect the predation rates of prey within the area. In particular, blooms of Physalia phsalis significantly affect the populations of fish due to the predation on a major portion of larvae within densely populated regions of their environment.

In addition to being an effective predator, the Portuguese man o’ war becomes an effective prey due to its slow, passive movement. Apart from the toxic sting, it has minimal defense at best, with a delicate, jelly-like body. The most common predators for the Physalia physalis are sea turtles, whose mouths are lined with papillae made of keratin. These hard projections throughout the mouth and throat negates the stings that would otherwise paralyze or kill other species. They also use their flippers in order to push away any stinging tentacles that try to make their way towards their more vulnerable neck and face while eating. Loggerhead and leatherback turtles will flock to areas with high densities of Portuguese man o’ wars for predation.

A Loggerhead sea turtle consuming a Portuguese Man o' War

More interesting predators to the Portuguese man o’ war are species of sea slugs, Glaucus atlanticus and Glaucilla marginatus, that are able to not only consume nematocysts but also incorporate them into their own bodies for self-defense. After consuming the nematocyst cells, they house them in the tips of many projections on their bodies called cerata. When threatened, the sea slugs can release the cells, causing a sting even more severe than a normal sting by a Portuguese man o’ war due to the concentrated nature of the stored cells.

A sea slug consuming the nematocysts of a Portuguese Man o' War

Now that we’ve explored the relationships that the Portuguese man o’ war shares with various sea dwelling creatures, stay with us for a deep dive into their exciting interactions with one of the most well-known species: human beings.

Works Consulted

The Portuguese Man o' War Predator/Prey Interactions

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