An Invasion of the Naked Sea Butterflies

By Terri Kirby Hathaway

Posted Aug. 1, 2016

Naked sea butterflies invaded the northern Outer Banks in late July, along with cooler 60 degree F water. Clione limacina are shell-less mollusks. They are neither eggs nor jellies, and do not sting. Also called sea angels, they are completely harmless!

These distinctive Arctic creatures, related to snails and sea slugs, are tiny, translucent animals, roughly 1 to 2 inches long. They look like ice cream cones with small wings that help them swim. Their heads and tails are orange-red in color. The visceral mass — which contains the digestive, respiratory, excretory and reproductive organs — is a darker brownish-orange.

Naked sea butterflies are normally found from the Arctic to Cape Hatteras, so North Carolina lies at the southern extent of their range. They thrive in water temperatures between 28 and 63 F.

Even though they are small, these animals are voracious predators. They feed on shelled sea butterflies by catching them, holding onto the shells and pulling the animals out. In turn, naked sea butterflies are food for baleen whales such as humpbacks and bowheads.

These delicate animals are protandrous hermaphrodites. Each individual contains male and female reproductive organs. They start out as males and develop eggs as they grow. After the eggs are fertilized, the sea angels release gelatinous egg strings into the water column where they float until they hatch. The larvae have a small shell when they hatch, but it is cast off after a day or two.

So, how did these beautiful tiny creatures invade our waters? After several days of strong winds from the west or southwest, the warm surface waters on the Outer Banks were blown offshore. Colder, nutrient-rich water located deeper below the surface rose up in its place. This process is called upwelling. Check out NOAA National Ocean Service’s excellent visual representation of this process at oceanservice.noaa.gov/facts/upwelling.html.

When the cold water moves up from the deep to replace the warm surface water, it tends to bring interesting things — such as naked sea butterflies, salps or other cold-water creatures — with it.

The ocean changes day to day; it is a very complex and dynamic system with many variables. This is why I am infatuated with the ocean and everything in it. How can you not be curious about and connected to something that is constantly changing and offering up new discoveries?

Here’s to the invasion of the naked sea butterflies! What’s next?

Mother, mother ocean, I have heard you call.
– “A Pirate Looks at Forty,” Jimmy Buffett