Honolulu Star-Advertiser © Susan Scott
October 5, 2019
My neighbor commented this week that in her 20 years in Hawaii, she’s never seen so many Portuguese men-of-war wash up on the beaches like they did this summer.
But we old-timers have. In 1994 the Honolulu City and County lifeguards treated approximately 6,500 Portuguese man-of-war sting victims. I know this because in 1997 my physician husband and I published that number, derived when working with Ocean Safety, in a book about Hawaii’s marine injuries called “All Stings Considered.”
The Portuguese man-of-war’s eating parts, reproductive organs
and stinging tentacles hang below its float. As it sails along the water’s
surface (the sail isn’t visible in the picture), the creature trolls for fish,
sometimes getting shipwrecked before it can eat its catch (inset).
©2019 Susan Scott
During an internet search, I found a 2009 Hawaii News Now article warning beachgoers of PMOWs. A science site search revealed reports of more-than-usual numbers of the creatures washing ashore in Venezuela in 2007, France in 2012, Brazil in 2013, Chile in 2015 and more.
So are there more of these creatures now than in the past? And since most of the animals we saw this summer were juveniles, did they have a bloom?
No one knows. Because their habitat is the surface of the world’s oceans, which occupies 71% of the planet, three times the area of land, studying these animals is difficult in the extreme.
PMOWs are one of several poorly understood offshore species (the blue dragon, for another) that drift with wind and current in tropical and subtropical oceans. These tough animals can survive intense UV exposure, battering waves and hurricane-force winds.
A PMOW’s bubble float is filled with carbon monoxide and air, a mixture controlled by a gas gland under the float. On the bubble’s top rests a pink sail that propels the individual either right or left. When the wind blows, the PMOW sets sail, and in this way can travel thousands of miles across open ocean.
When conditions bring the animals near islands or coastlines, and onshore winds develop, the PMOWs run aground.
As to why we saw so many little ones this summer, it’s unknown whether there’s any seasonality to PMOW reproduction. Researchers do know that each individual float is either male or female. When the time is right, adults cast their mature gonads into the sea where, like countless other marine species, the eggs and sperm get lucky and connect, or become food for plankton eaters.
Tiny PMOWs grow underwater until the bubble gets big enough to float the creatures, their body parts hanging below like squiggly blue strings. One of the longer strings is the animal’s fishing line, armed with stinging cells that we swimmers know all too well.
In the 2019 collaborative study I read for this column, the five research scientists conclude with this:
“Most of our experiences of the Portuguese man-of-war are close to shore, where news stories warn of purple flags, vicious stings, and ruined beach days, however, we still know almost nothing about their behavior, ecology, and lifecycle out in the open ocean.”
We do know, however, that they’re crackerjack sailors.