Meet one of the ocean's most intriguing biological mysteries | ECOVIEWS

Whit Gibbons
·3 min read
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From an ecological perspective, our oceans are as special as our land.

Seawater makes up more than 70% of the Earth’s surface. Oceans teem with an enormous variety of animal groups poorly known to science and myriad creatures seldom seen even by ecologists.

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The nudibranchs are one such group. Among the 3.000-plus described species are the regal sea goddess, Spanish dancer and blue sea dragon. These remarkable creatures, which range in size from 1/8th of an inch to almost 2 feet, include some of the most colorful animals in the world. Some are drab in appearance, but some are strikingly beautiful.

A sea creature known as the Neapolitan nudibranch, found in the Atlantic Ocean, Mediterranean Sea and Gulf of Mexico, is one of thousands of species of oceanic mollusks without shells. [Photo provided by Parker Gibbons]
A sea creature known as the Neapolitan nudibranch, found in the Atlantic Ocean, Mediterranean Sea and Gulf of Mexico, is one of thousands of species of oceanic mollusks without shells. [Photo provided by Parker Gibbons]

I have only seen one nudibranch, in an Atlantic coastal marsh. Most of the world’s 8 billion people have never seen or even heard of one.

The name itself is unfamiliar to many biologists, but its etymology is useful in understanding what a nudibranch is. The derivative of the word nudibranch is obvious from the Latin words “nudus” meaning naked and “branchia” meaning gill. Nudibranchs are mollusks, like clams, snails and oysters, but as adults they have no shell, so their soft body and gills are completely exposed.

Though unfamiliar to most of us, nudibranchs have a worldwide geographic range that encompasses a greater area than all insect species combined. They are found exclusively in saltwater habitats from the Arctic Ocean to the Southern Ocean in Antarctica.

Not unexpectedly, most have been found on the surface where they are more easily accessible to researchers who look for them. But deep-sea exploration has found nudibranchs at depths of more than 1 mile.

In 2022 ,the Monterey Bay Aquarium Research Institute reported a new species of nudibranch near the Gulf of California crawling on the ocean floor at a depth of more than 7,700 feet. All nudibranchs are carnivorous, many feeding on sponges and corals. What they may be eating in the midnight zone of the ocean has not yet been determined.

On the other side of the predator/prey coin is this question: How do gorgeous animals with no protective shell living in a sea full of hungry fish, crabs and other predators keep from becoming tasty morsels themselves?

Scientific research has revealed some of their defense mechanisms. As with many animals, camouflage is a frontline strategy. Don’t be seen; don’t be eaten. Many nudibranchs roam around looking like whatever their background is. Others undoubtedly use chemical warfare, making them distasteful or even toxic. The most intriguing, as reported in the Sea Slug Forum of the Australian Museum, are nudibranchs that prey on jellyfish or other sea creatures that boast stinging cells called nematocysts.

Blue sea dragons are stunning nudibranchs, floating in warm oceans around the world. Although obvious to any animal with vision, few predators make a snack of one of these curiously shaped, blue and white nudibranchs. Why? Because blue sea dragons give new meaning to the adage "you are what you eat."

In the Atlantic and Pacific oceans, they prey on the deadly Portuguese man-o-war. In marine waters of the Indo-Pacific they eat the man-o-war’s counterpart, the bluebottle jellyfish. Although the mechanism is not fully understood, a blue sea dragon consumes nematocysts without harm and incorporates them into its own body, transforming itself into a creature with an arsenal of stinging cells.

The ocean is full of intriguing biological mysteries. Big stuff like colossal squids, leatherback sea turtles and orcas that attack sailboats for what may simply be teenage sport. The ocean also contains tiny creatures with fascinating lives that most of us will never know about.

Maybe if more people knew about the captivating nudibranchs, we would be more careful about the way we debase the seas of the world with garbage, plastic bags, pesticide runoff and a thousand other unsavory assaults.

Nudibranchs are very cool. If we can keep our oceans clean, maybe one day you’ll get lucky and get to see one.

Whit Gibbons is professor of zoology and senior biologist at the University of Georgia’s Savannah River Ecology Laboratory.
Whit Gibbons is professor of zoology and senior biologist at the University of Georgia’s Savannah River Ecology Laboratory.

Whit Gibbons is professor of zoology and senior biologist at the University of Georgia’s Savannah River Ecology Laboratory. If you have an environmental question or comment, email ecoviews@gmail.com.

This article originally appeared on The Tuscaloosa News: What you should know about the intriguing nudibranch | ECOVIEWS