Portuguese Man o' War | Oceana
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Marine Life Encyclopedia

Corals and Other Invertebrates

Portuguese Man o’ War

Physalia physalis

Distribution

Worldwide in tropical to temperate latitudes

ECOSYSTEM/HABITAT

Coastal to open ocean (pelagic)

FEEDING HABITS

Foraging predator

TAXONOMY

Class Hydrozoa (hydrozoans), Family Physaliidae (men o’ war)

The Portuguese man o’ war is a highly venomous open ocean predator that superficially resembles a jellyfish but is actually a siphonophore. Each man o’ war is actually a colony of several small individual organisms that each have a specialized job and are so closely intertwined that they cannot survive alone. In this manner, the larger colony consists of a float that keeps the colony at the sea surface, a series of long tentacles that are covered with stinging cells, a rudimentary digestive system, and a simple reproductive system.

The Portuguese man o’ war is a predatory species. It uses its feeding tentacles to sting and paralyze small fishes, pelagic crustaceans, and other invertebrates. The feeding tentacles may be up to 160 feet (50 m) long in some individuals! These tentacles deliver a powerful sting and are also used for defense against predation. Few species eat the Portuguese man o’ war, but some predators that specialize on stinging, gelatinous invertebrates (e.g., loggerhead sea turtles and ocean sunfish) are known to feed on this and other siphonophores.

Each individual Portuguese man o’ war is either a male or a female, and they reproduce sexually via a method known as broadcast spawning. Large groups of individuals come together, where females release their eggs and males release their sperm into the water column, all at the same time. This method increases the likelihood that eggs will be fertilized.

The Portuguese man o’ war is not valuable, commercially, and is common throughout the tropics. In some places, it is increasing in numbers, likely a result of changing open ocean food webs. This species’ sting can be very painful if encountered by people. When there are large numbers of individuals in an area, it is best to avoid swimming.

Fun Facts About the Portuguese Man o’ War

1. The Portuguese man o’ war is not a jellyfish, but rather a siphonophore, which is a colony of specialized animals called zooids that work together as one.

2. The Portuguese man o’ war doesn’t swim. Instead, it uses wind and ocean currents to propel it forward.

3. The Portuguese man o’ war was named after its resemblance to 18th century Portuguese warships.1

4. The Portuguese man o war’s float can be up to 6 inches (15 cm) tall.

5. The Portuguese man o’ war’s tentacles grow as long as 165 feet (50 m).2

Engage Youth with Sailors for the Sea

Oceana joined forces with Sailors for the Sea, an ocean conservation organization dedicated to educating and engaging the world’s boating community. Sailors for the Sea developed the KELP (Kids Environmental Lesson Plans) program to create the next generation of ocean stewards. Click here or below to download hands-on marine science activities for kids.

Kids Environmental Lesson Plans

References:

1 NOAA Ocean Facts

2 South Carolina Department of Natural Resources

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