Tag Archives: Portuguese man-of-war

Man-of-wars are 1 animal, not a mishmash of critters

Published September 17, 2016 in the “Ocean Watch” column, Honolulu Star-Advertiser ©2016 Susan Scott

At the beach, I recently ran into my neighbor, Marya, who, as usual, had a thoughtful marine animal question. She wondered how it is that a Portuguese man-of-war is a colony of individuals rather than one animal.

“I can’t picture how that works,” Marya said.

I can’t picture it, either, but we don’t need to because it’s an old idea. Besides that, the confusing colony statement detracts from the fact that the Portuguese man-of-war is one of nature’s most exquisite masterpieces.

A man-of-war starts life when a drifting sperm meets a drifting egg and grows into a larva, a flat bean-shaped thing with swimming hairs.

As it matures, the front end of the larva transforms into a blue, air-filled bubble topped with a fleshy pink sail that the creature trims to move at an angle to the wind. When strong tradewinds and storms overpower the little sails, man-of-wars get shipwrecked on our beaches.

While forming its float, the larva also produces, from below, three types of tentacles. One type contains sperm and eggs (man-of-wars are hermaphrodites). Another kind has long tentacles with stinging cells. The third tentacle type consists of hollow eating tubes.

As the creature sails around the ocean surface, its stinging tentacles troll below for small crustaceans and fish. When it gets a catch, the retractable tentacles reel it in to the eating tentacles, which wrap around the food.

Normally having openings invisible to the naked eye, the mouths of man-of-war eating tentacles can expand to three quarters of an inch. After spitting enzymes on the prey to externally digest it, the food tubes suck up the meal.

Most animals function similarly, having a nerve-directed team of genetically identical, but specialized, organs dependent upon each other to live and reproduce. But because the man-of-war grows its float and tentacles by budding (pooching out) from its larva, some biologists in the past declared that each pooch was an individual animal, even though each does a different job and none can live alone. It’s like saying our stomach is one person, our gonads another and limbs another.

Although the statement that each man-of-war is a colony rather than an individual is pervasive, it’s not written in stone. My favorite invertebrate zoology textbook authors write “ … that it sometimes seems more appropriate to consider the colony (of siphonophores, man-of-war and their clan) as one complex individual.” And the authors of my Monterey Bay Aquarium go-to book on gelatinous animals write that although it’s still debated, “ … most specialists now prefer to think of (siphonophores) as individuals with many well-integrated parts.”

Now that we can picture. Thanks, Marya, for another great question.

Violet snails build their own bubble rafts and float away

Published November 9, 2015 in the “Ocean Watch” column, Honolulu Star-Advertiser ©2015 Susan Scott
Violet snails shells are left behind by animals that survive by eating Portuguese men-of-war.©2015 Susan Scott

Violet snails shells are left behind by animals that survive by eating Portuguese men-of-war. ©2015 Susan Scott

AIRCRAFT BEACH, EURIMBA NATIONAL PARK, Australia » For me, beach walking is often as rewarding as snorkeling. Sure, marine animals lying on beaches are dead or dying, but that means I can pick them up or turn them over and admire to my heart’s content. The long-dead animals I found stranded on this 2-mile-long sand beach, suitable for small plane landings, are the largest violet snail shells I’ve ever seen, nearly 2 inches long and an inch high. The exquisite shells, lavender above and purple below, lay 50 or so feet above the high tide line, suggesting that storm winds drove the snails toward shore and high waves spit them out. Most violet snails have better luck. Healthy ones float offshore, upside down, on self-made bubble rafts. Some believe that the snail agitates water with its foot to make bubbles. Another theory is that the snail blows bubbles from air it has taken into its shell. In either case, the creature secretes mucus from its foot to coat its bubbles, creating a rubbery raft.

It’s a precarious existence. To lose the raft is to sink to the bottom and drown. These air-breathing snails can’t swim.

Nor can they steer. Throughout the world’s tropical oceans, violet snails and other members of their drifting community, including Portuguese men-of-war (called blue bottles here in Australia), are at the mercy of winds and currents. That’s why during strong onshore winds, we find both species stranded on beaches.

Unlike us, violet snails don’t get a sting when they bump into blue bottle tentacles. They get a meal. Portuguese men-of-war are violet snails’ main food.

When an animal can’t control its course, it’s tough for the sexes to get together. As a result, when a male violet snail senses a female in the area — they can’t see each other because violet snails have no eyes — he ejects sperm in her general direction. When the sperm hit their target, the female lays eggs and carries them with her beneath her bubble raft.

Eggs hatch into a drifting underwater form. When they mature, the tiny snails build their own bubble rafts and continue the nomadic existence.

I’ve often found violet snail shells on Hawaii’s windward beaches, and could fit about 10 in my palm. Here two barely fit. The snails might be different species, or the big ones might have grown large due to these nutrient-rich waters. On the same beach, I also found the biggest Portuguese man-of-war I’ve ever seen. Whatever their size, violet shells on any beach give me a fine marine animal fix. And I don’t even have to get wet.


Marine biologist Susan Scott writes the newspaper column, “Ocean
Watch”, for the Honolulu Star-Advertiser, www.staradvertiser.com

©2015 Susan Scott