Watch Barnacles Host an Underwater Light Show While Feeding on Bioluminescent Dinoflagellates

by Owen James Burke

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Screenshot from Orca’s YouTube video.

Barnacles, those jagged calcified things on rocks and pilings upon whom we always seem to cut ourselves, they don’t do all too much, do they? No, not really. But watch again, more closely, and you might find something of intrigue.

Growing up near the mouth of the Hudson River, I didn’t get too see too much aquatic life through the silt- and mud-stained waters, apart from what I hooked and pulled aboard Blues Dory. A trip to the Bahamas as a young teen left me enamored by the corals and polyps of clear water and tropical reefs. I didn’t want to go home to the murky waters of Long Island Sound.

Then, some time after my tropical enlightenment, my marine biology class took us to the town docks, where I kept my skiff. Our instructor told us to peer over the edge, into the water. It was incredible, something I had stepped over day-in and day-out during my summers, had gone completely over my head, or under the soles of my shoes.

Thousands of barnacles, of which I had never thought anything more than a nuisance were flailing their cirra, or tiny arms about like the corals and polyps in the reefs I’d seen in the Bahamas.

Barnacles are fairly simple organisms; they don’t even have gills. Their gaseous exchanges take place by propulsion driven by their cirra, which are also the mechanisms used to trap prey. In the video below, barnacles are capturing a bioluminescent dinoflagellate which, when its nucleus is disturbed, gives off a flash of light. A single swipe of the small crustacean’s tiny arms and hundreds of these dinoflagellates are disturbed, causing an underwater light show spectacular.

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