A Look at the Portuguese Man o' War and Mutualism

A great example of symbiosis

After our deep dive into the evolutionary history of the Portuguese Man O’ War, we will float on down to a couple of ecological topics on this fascinating species.

The Portuguese Man O’ War has a special relationship with several different species; this relationship is known as mutualism. Why is this mutualistic relationship important? Mutualism is a positive interaction between two species in which each of the species involved receives a benefit only the other species can provide. In a mutualistic relationship, there are fitness benefits for both parties. The Portuguese Man O’ War has a special relationship with the Nomeus gronovii, yellow jack, and clown fish. The Portuguese Man O’ War and these fish have a mutualistic relationship which is a type of symbiotic relationship. In a symbiotic relationship, two different organisms live in close physical association. The key difference between mutualism and symbiosis is that in a mutualistic relationship both organisms provide a benefit for one another.

We will focus specifically on the interactions of the Portuguese Man O’ War and the Nomeus gronovii (these interactions can be applied to the other fish as well). Another name for the Nomeus gronovii is the Bluebottle-fish. At a young age, they tend to be pelagic, meaning they inhabit the upper layers of the ocean. The adult fish are demersal, which means they live close to the ocean floor. A special experience occurs when the Bluebottle-fish are juveniles and live among the tentacles of the Portuguese Man O’ War.

A close look at the interactions between the Nomeus gronovii and the Portuguese Man o' War

The blue-bottle fish are identified by their compressed body with a large forked caudal fin. Their pelvic fins are similar to large fans. The Nomeus gronovii are resistant to the poison produced by the stinging cells of the Portuguese Man O’ War. However, the Nomeus gronovii do avoid the large tentacles to prevent themselves from getting stung. The main difference between the Nomeus gronovii and the clown fish’s relationship to the Portuguese Man O’ War is the way they are able to resist the stinging tentacles. The Nomeus gronovii are partially immune to the poison. Other marine fish, like the clown fish, can swim amongst the tentacles due to the mucus they secrete that does not trigger production of the poison from the nematocysts. The Nomeus gronovii tend to swim close to the small tentacles underneath the bladder of the Portuguese Man O’ War.

The Nomeus gronovii, also known as the Bluebottle-Fish

Now that we have defined what species are involved in the mutualistic relationship, we can determine how each species benefits. These species benefit in a facultative manner in that they provide an increase in fitness for each other, yet they can still survive on their own without the mutualism. The Portuguese Man O’ War and these several species of fish are specialists, since not all fish are resistant to the stinging tentacles. It takes a certain type of fish to take part in this mutualism. If this were a generalist relationship, we would see the Portuguese Man O’ War interact with many more species of fish. The Portuguese Man O’ War benefits through resource acquisition. The presence of the Nomeus gronovii swimming beneath the Portuguese Man O’ War attracts other fish that are not resistant to the stinging tentacles. When these fish swim close to the Portuguese Man O’ War, they are poisoned by the nematocytes and will become food for the Portuguese Man O’ War. The fish, such as the Nomeus gronovii, benefit in multiple ways such as resource acquisition and protection from enemies. The Nomeus gronovii are protected from enemies by swimming close to the stinging tentacles; other species do not dare to enter for fear of paralysis. The Nomeus gronovii can befit from resource acquisition by feeding off some of the small tentacles and any of the nutrients provided by the Portuguese Man O’ War that they did not consume. Together, these species work together to aid in each other’s fitness. If you are excited continue our adventure exploring these fascinating creatures, stay tuned!

Works Consulted

A Look at the Portuguese Man o' War and Mutualism

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