Weird and Wonderful Nudibranchs
January 22, 2024
By Paul Erickson
Rainbow Nudibranch, tropical Indo-Pacific. Photo © by Birgitte Wilms.
Quirky people fascinate me.
Purple-lined Nembrotha, tropical Indo-Pacific. Photo © by Birgitte Wilms.
Take certain kinds of collectors. Some collect snippets of rusty 19th-century barbed wire. Others swipe barf bags (unused), printed with company logos, from commercial airlines. Still others find it appealing to gather banana label stickers, keeping them in treasured volumes like stamp collections.
Then there are quirky scuba divers, like me, obsessed by nudibranchs (NOO-dee-branks or NOO-duh-branks)—small ocean-going mollusks without shells that topsiders (normal people) irreverently call sea slugs. Some fellow nudi-fanatics pay tens of thousands of dollars to fly tens of thousands of miles to find and photograph these creatures, most of which are no bigger than the blossom of a pussy willow.
So what’s the attraction? For one thing, they comprise a living art museum. Many display gorgeous, psychedelic, tie-dye-like color combinations. One species looks like a Chinese New Year dragon. Another is the spitting image of Shaun the Sheep in Wallace and Gromit movies. Both scientists and amateur, citizen-scientist divers discover new nudis every year. They’ve discovered more than 3000 species.
While most nudibranchs live in tropical waters, many prowl the submerged sands, rocks, crevices, and miniature seaweed jungles surrounding Cape Ann. Only the most observant divers have the ability and patience to find them.
So, for some advanced expertise regarding our local nudibranchs, we interviewed Jerry Shine—one of New England’s most avid and experienced divers. Jerry downplays his knowledge of our local nudibranchs. Yet as modest as he is, Shine wrote the superbly researched book Nudibranchs of the Northeast, featuring his fantastic close-up photographs.
Jerry Shine, cold-water diver and former merchant marine ship captain with some of the underwater camera gear and strobe lights he uses to photograph nudibranchs. Photo © Jerry Shine.
As a result of his dedication and countless hours enduring cold northwest Atlantic waters, even in winter, Jerry knows some 28 or more species of Gulf of Maine, and specifically Cape Ann nudibranchs, as well as you might know the names of birds visiting your feeder.
Beyond his masterful photos accompanying this brief essay, Jerry is also fascinated by the remarkable behaviors of these little beasts. For example, a number of Cape Ann nudibranchs have spicy diets and quirky table manners. They dine on stinging hydroids and sea anemones—close relatives of venomous corals and sea jellies.
“When you first look at nudibranchs, they appear to have no natural defenses,” says Jerry. “But they are anything but defenseless. When some of our local varieties attack and nibble on hydroids, for example, they steal the hydroids’ weapons—microscopic, explosive, venom injecting stingers called nematocysts. Then they move the stingers through their bodies and into frilled structures on their backs.” (Note: Our local hydroids can’t sting people; our skin is too thick.)
Remarkably, nudibranchs achieve this maneuver without triggering the stingers.
Subsequently, when a fish attempts to eat a nudibranch hors d’oeuvre, it triggers the purloined stingers and, in pain, instantly spits out its would-be victim, which is usually no worse for the wear.
Accompanying these words are some of Jerry Shine’s photos of nudibranchs found off the coast of Cape Ann along with pictures of tropical varieties photographed in distant seas by New Hampshire diver Birgitte Wilms.
I hope you’ll agree that nudibranchs display the beauty and elegance sculpted and painted by the greatest artist of all—the artist we call nature.
One way of spotting tiny nudibranchs is to look for their egg masses, often forming spirals—an elegant example of animal architecture. Photo © Jerry Shine.
One of our local nudibranchs dines on tiny, flower-like, stinging animals called hydroids. Photo © Jerry Shine.
A nudibranch slurps up pink-hearted hydroids like candy. Photo © by Jerry Shine.
PAUL ERICKSON
Science Editor
Paul trained in life sciences at Bates College and is a natural history writer, diver, and photographer. He worked at the New England Aquarium for 26 years and served as an on-camera correspondent for many programs, including ABC’s Good Morning America and WBZ-TV’s Eyewitness News, Evening Magazine. He has also worked as an educator at the Glen Urquhart School and aboard the Salem-based Sea Shuttle Endeavour. Paul has photographed underwater habitats in the Red Sea, Solomon Islands, Fiji, Belize, the Philippines, New England and Loch Ness, Scotland. His latest books, published by Tilbury House, are Don’t Mess with Me: The Strange Lives of Venomous Sea Creatures and The Pier at the End of the World. Paul lives in Ipswich.
