NUDIBRANCHS ARE BIZARRE OCEAN CREATURES
Whit Gibbons
Q. I enjoy learning about bizarre animals like the terrestrial one you recently wrote about called a hammerhead worm. With all the strange animals found on land, the oceans must be full of even more creatures most people have never seen or heard of. What are some of your favorites?
A. You are correct that the world’s oceans are home to a seemingly endless array of poorly understood life-forms and myriad unfamiliar creatures. My list of favorites would be too long for this column but would certainly include the nudibranchs. Nudibranchs are gastropod mollusks, like mussels, clams and scallops, but as adults they have no shell, so their soft body and gills are completely exposed. I’ve never heard of anyone eating a nudibranch. My grandson Parker has found several spectacular examples in the Atlantic Ocean.
These remarkable creatures, of which more than 3,000 have been described, range in size from 1/8 of an inch to almost 2 feet and include some of the most colorful animals in the world. Though some are drab in appearance, some are strikingly beautiful. I have seen one nudibranch, in an Atlantic coastal marsh, which puts me (and Parker) in the small percentage of the world’s 8 billion people who have ever seen, or maybe even heard of, one.
Though unfamiliar to most people, nudibranchs have a worldwide geographic range 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 crawling on the ocean floor near the Gulf of California at a depth of more than 7,700 feet. All nudibranchs are carnivorous, many feeding on sponges and corals. What they might eat 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 does a gorgeous animal with no protective shell, living in a sea full of hungry fish, crabs and other predators keep from becoming a tasty morsel? 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 example, as reported in the Sea Slug Forum of the Australian Museum, are nudibranchs preying on jellyfish or other sea creatures that boast stinging cells called nematocysts.
For example, blue sea dragons are stunning nudibranchs found 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. Scientists do not fully understand the mechanism, but 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 (or may not) simply be teenage sport. And tiny creatures that most people will never know about. Maybe if more of us knew about the captivating nudibranchs, we would be less likely to 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.
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