Portuguese Man o' War

By Danielle Devonport

Niche and Habitat

The Portuguese Man o' War floats along the surface of tropical, marine waters. These colonies are generally found living in warm tropical and subtropical water such as along the Florida Keys and Atlantic coast, the Gulf Stream, The Gulf of Mexico, and the Indian Ocean, the Caribbean Sea. They are especially common in the warm waters of the Sargasso Sea. Their habitat makes up 71% of the Earth's surface and is nearly three times the area of all terrestrial habitats.

This predatory species feeds mainly on juvenile fish, small adult fish, shrimp, pelagic crustaceans, and other invertebrates. Nearly 70 to 90% of their prey is fish. They use their feeding tentacles to sting and paralyze their prey. Few species eat the Portuguese man o' war, but some predators include loggerhead sea turtles and ocean sunfish.

Environmental Impacts

With more and more Portuguese man o' war washing up on shore and higher numbers of colonies in the oceans, humans and the surrounding beach environments are at great risk. In human beings, typical lesions that arise immediately after contact with a Portuguese man-of-war (i.e., while still in the water) include linear plaques and excruciating pain. In some cases, envenomation can induce systemic manifestations such as nausea and vomiting, cold sweating, cardiac arrhythmia, syncope, and death. In addition, allergic responses to venom may manifest as anaphylactic shock, leading to death within minutes. The PMOW's that wash up on shore, are still able to sting and should be avoided at all costs.

Friends or Foes?

A small fish called the man o' war fish, Nomeus gronovii, is partially immune to the venom from the stinging cells and can live among the tentacles. It seems to avoid the larger, stinging tentacles but feeds on the smaller tentacles beneath the gas bladder. This fish and a variety of other marine fish benefit from the shelter from predators provided by the stinging tentacles, and for the Portuguese man o' war, the presence of these species may attract other fish to eat.

The thick-skinned loggerhead sea turtles, ocean sunfish, and "blue dragon" sea slugs are considered the top predators of this species. The "blue dragon" sea slug has been known to devour the Portuguese man o' war and actively harvest and appropriate its toxins. After storing the man o' war's stinging cells in their skin, they use it as a predator deterrent.

Web Resources for Audience to Explore

National Geographic: Portuguese Man-of-War

National Geographic is the official magazine of the National Geographic Society. It primarily contains articles about science, geography, history, and world culture.

Animal Diversity Web (ADW): Physalia physalis

ADW is an online database of animal natural history, distribution, classification, and conservation biology at the University of Michigan. It is an online encyclopedia, a science learning tool and facilitates inquiry-driven learning, and a virtual museum.

Oceana: Portuguese Man o' War

Oceana is an international organization focused solely on oceans, dedicated to achieving measurable change by conducting specific, science-based policy campaigns with fixed deadlines and articulated goals. Their website has a marine life encyclopedia section on their website.

Sailors of the Sea: Kids Environmental Lesson Plans (KELP)

Sailors for the Sea Powered by Oceana is a conservation organization that engages, educates and activates the sailing and boating community toward restoring ocean health. Kids Environmental Lesson Plans (KELP) are downloadable activities that educate junior sailors and school children about marine science and give them the tools to learn, discover and protect our precious waterways. The lessons are easy to teach and use items found around the house or sailing center.

NOAA

NOAA stands for the National Oceanic and Atmospheric Administration. Their mission is to provide science-based solutions through collaborative partnerships to address evolving economic, environmental, and social pressures on our ocean and coasts.