Snorkeling off the coast of the Florida Keys is a thrilling experience for anyone interested in the natural world. Coral reefs are the “rainforests” of the sea: complex ecosystems teeming with oodles of colorful species. I could go on and on about the creatures I saw: sea turtle, dolphin, nurse shark, barracuda, hogfish, parrotfish, damselfish, butterfly fish, flying fish, wrasse, snapper, tang, frigate bird, pelican, tern, sea urchin, sea star, sea squirt, and of course coral, which is itself made from little colonial animals. However, I’d like to focus on one critter of which I was particularly aware: the Portuguese Man-of-War.
The PMW, a relative of jellyfish, has three notable characteristics. First of all, like many of its kin, it stings. I avoided any tactile encounters, but my brother took a direct hit from a tentacle that wrapped around the front and back of his torso, leaving a red mark that lasted a week. He said it was like a line of bees all stinging repeatedly. Although severely painful, these stings are rarely fatal, and we were brave enough return to the water. Because they move slowly and are a striking bluish-purple color, PMWs are easy to spot and avoid once you start paying attention.
The second notable feature of the PMW also helped us to steer clear of it. The PMW has a large gas bladder with a sail that floats on the ocean surface and is blown by the wind. This balloon looks like a Portuguese ship, hence the name. Because it relies on the wind for transportation, it ends up wherever the wind happens to be blowing: washed up on the beach, or against a cliff on the windward side of the shore. At Dry Tortugas National Park, dozens of PMWs were collecting where the sea laps against the outer wall of the abandoned military fort, apparently blown there by the wind. Several swimmers were getting stung, but these all seemed to be people swimming near the wall. By swimming farther out, we escaped this marine hornet’s nest and enjoyed water nearly free of PMWs.
The cool part about this scenario is that one can walk along the short outer wall and look down at the bobbing group of PMWs (and even shout warning to approaching naïve snorkelers, if one is feeling benevolent). They are close enough to reach down and touch, if you’re dumb enough to do so. I noticed that when two PMWs bumped into each other they stuck, such that there were several little clumps of PMWs. Small PMWs were especially likely to form clumps, while the big ones were more often solitary. This brings up the third, and most fascinating, fact: the PMW is actually a colony of polyp animals, not a single animal. The polyps cooperate so well that they act just like a unified individual, not the committee that they are. We are accustomed to thinking of living organisms as distinct entities, but the PMW shows how arbitrary this distinction can be. Is each polyp an “individual,” or are they just parts of a whole, the way that an animal’s cells are not thought to be unique organisms? Does that question even have a real answer? The addition of a new hierarchical level of organization can be an important evolutionary step (as in the evolution of multicellularity itself)… the little PMW is arguably more complex than we are, and its status as a “superorganism” could allow it to take evolutionary paths not available to simple organisms. For example, the clumps of PMW I observed made me think about the colonial nature of this species, and wonder if some of those clumps might be able to rearrange themselves into a single large PMW (the colony is usually formed from asexual budding, but could there be another way?).
As we have noted before here at SC, there is something exciting and primal about being around dangerous species. Even a swimmer’s bane like the PMW is a wonderful and bizarre wild creature to be respected and even appreciated.