Hakai Magazine

barnacles on a humpback whale's tail fluke
A group of barnacles lives a mobile existence, attached to the skin of whales such as this humpback. Photo by Matthew Maran/Minden Pictures

What Whale Barnacles Know

For generations, these hitchhikers have been recording details about their hosts and their ocean home.

Authored by

by Mara Grunbaum

Article body copy

In the grand scheme of things, Michael Moore regrets losing his sense of smell decades ago as the result of chemical exposure in veterinary school. It may have spared him some discomfort, though, on the day in September 2010 when he arrived on a beach in Massachusetts to examine the colossal decaying carcass of a washed-up humpback whale. The eight-meter animal had been found dead in Chatham, on the elbow of Cape Cod, and Moore, a veterinary scientist at Woods Hole Oceanographic Institution (WHOI), wanted to determine what killed it. But when he reached the gigantic cadaver, he found that its organs had already decomposed too much for him to glean much of use. He did see one sign of life, however: clusters of freeloading whale barnacles, embedded in the whale’s skin like calcium carbonate body piercings. Their shells clicked softly as they extended their feathery back legs, sweeping the air for plankton that were no longer floating by.

Whale barnacles are a specialized family of acorn barnacles, the filter-feeding marine crustaceans that affix themselves to various surfaces and encase their soft bodies in volcano-shaped shells. Like the whales they live on, whale barnacles can grow to dramatic proportions compared with the species you might see on the seashore. “They’re the size of a small coffee cup, and they’re quite spherical, like imploded tennis balls,” Moore told me. “If you’re into barnacles, they’re pretty extraordinary, because they’re so big.”

close up of barnacles on pectoral fin of a humpback whale

Some species of whale barnacles can grow to be about the size of a clementine orange. They attach as larvae and then grow calcareous plates that embed in the whale’s skin. Photo by Bertie Gregory/Minden Pictures

Moore, by his own admission, is not into barnacles—in fact, he hates them. He comes by his disdain honestly, having spent countless hours trying to remove the stubborn invertebrates from the propellers of his boats. But he knew who would appreciate the critters still alive and clinging to the whale carcass: Jesús Pineda, an ocean ecologist at WHOI. Moore sliced off a few barnacles with a long knife, placed them on ice in a cooler, and shuttled them back to WHOI’s seaside campus to hand off to his colleague.

Pineda, who has built an academic career on being into barnacles, was excited. Of the 1,000-plus species of barnacles on Earth, whale barnacles are some of the most difficult ones to find—and therefore study—while they’re still alive. Instead of spending their lives stuck in one spot like many of their relatives, whale barnacles hitchhike on the heads and flippers of migrating baleen whales and feed on the plankton that their mobile homes swim through. This arrangement also protects the barnacles from gulls, carnivorous sea snails, and other predators on shore. But because they can’t seal themselves shut like other species, whale barnacles don’t survive long out of the water. That makes it a lucky break to acquire living specimens even when a nonliving whale washes up. Plus, no one knows much about how to care for the barnacles once they’re detached from their blubbery bodyguards. Moore’s find presented a rare opportunity for Pineda to give it a try.

Pineda transferred the barnacles, bits of rotting whale still attached, to an open tank in WHOI’s Environmental Systems Laboratory. Seawater gently flowed over them, and Pineda laced it with freeze-dried brine shrimp—also known as sea monkeys—in the hopes of keeping the barnacles fed. He wanted to breed them and study how their larvae attach to whale skin. But after several weeks, the barnacles died without reproducing, and 11 years later, Pineda is still waiting for another shot.

Jesús Pineda, an ocean ecologist at Woods Hole Oceanographic Institution

Jesús Pineda, an ocean ecologist at Woods Hole Oceanographic Institution, is an expert in whale barnacles. The images on his computer are of barnacle larvae. Photo by Tom Kleindinst/Woods Hole Oceanographic Institution

For as long as humans have known about whales, we’ve also known about their barnacles. These unbudging appendages, which colonize a dozen-odd different whale species, latch on so tightly that they’re practically part of the whales’ skin. As a result, they were carried into caves by southern African people who foraged washed-up whale meat 164,000 years ago. They were described and sorted by Charles Darwin and Jean-Baptiste Lamarck in early taxonomic studies, and delicately illustrated in the works of Musashi Sekiju, a 19th-century samurai naturalist. They were even immortalized in literature by none other than Herman Melville: he describes the Pequod sailing alongside “the barnacled hulls of the leviathan” in a passage from Moby-Dick.

When it comes to modern scientific research, though, whale barnacles haven’t gotten much notice. There’s little money in them; the Nobel Committee is unlikely to call up whoever finally demystifies their quiet, vagabond lives. But for the handful of scientists who do work with them, they inspire a unique fascination. “I joke sometimes, when I give a talk or publish a paper, that all 10 people in the world who study whale barnacles will be really interested,” says Larry Taylor, a biology instructor at Helena College University of Montana.

Taylor, whose PhD research focused on fossilized whale barnacles, is one of a small group of scientists determined to learn more about these wayfaring creatures. Despite the hurdles involved in studying them—and there are many—they’re convinced that the overlooked animals have things to teach us about the whales they live on, the history of Earth, and what might be to come.

Here’s what we know about whale barnacles’ lifestyles: like all barnacles, they begin their lives as microscopic swimming larvae. At some point, they find a spot to settle and start building up a shell to protect their vulnerable bodies. They secrete six hard plates that fuse together into a wraparound retaining wall, with an opening on top through which they conduct all of their outside business. As the larvae grow into shrimplike adults, they add concentric rings of material to the bottom of the shell wall, expanding it into the mineral equivalent of a stacking-ring baby toy. They spend the rest of their lives with their heads glued in place, unfurling their leg-like cirri to filter-feed and using their long, flexible genitalia to mate with their neighbors. Many barnacle species do these things while attached to rocks, piers, mussel shells, or Michael Moore’s boat propellers. Whale barnacles do them on the surface of living whales.

Some barnacles, including the tassel-shaped species Xenobalanus globicipitus, can live on many different types of cetacean. Others are pickier, attaching mostly to whales of a particular species. Tubicinella major, which looks like a corrugated vacuum hose, lives almost exclusively on right whales. Coronula diadema—named by the father of taxonomy himself, Carl Linnaeus—prefers to settle on humpbacks. Each of these barnacles has a shell structure specially evolved to anchor itself into its host’s flesh. Many species have chambers within their wall plates into which prongs of whale skin grow upward, strengthening the barnacle’s grip.

Individual whales have been known to collect up to 450 kilograms of barnacles. That’s an enormous mass, but relative to a 30-tonne humpback, it would weigh only about as much as an extra layer of clothes. And as far as scientists can tell, the hangers-on don’t particularly bother a healthy whale. They may slightly increase drag as the whale swims, but they may also be helpful as a set of brass knuckles when adult males battle each other over the chance to mate.

close-up of a barnacle on a gray whale’s skin

This close-up of a barnacle on a gray whale’s skin shows the feathery feeding appendages, called cirri. The barnacle waves the cirri through the water to filter-feed on plankton. Photo by Mark Carwardine/Minden Pictures

Here’s what we don’t know about whale barnacles, at least with any certainty: just about everything else. Like, how do their larvae, no bigger than a grain of salt, find a migratory whale to grab onto in the first place? Once they locate one, how do they navigate around its gargantuan body—hundreds of thousands of times larger than theirs—to find their permanent homestead? “It just seems preposterous,” says John Zardus, a marine biologist at the Citadel in Charleston, South Carolina. He specializes in studying barnacles that live on other living things.

Studying those symbiotic barnacles that live on sea turtles, dolphins, crabs, and other marine animals has given Zardus some idea of how whale barnacles might hack it. Adults mate on the whale, but rather than take their chances during their host’s oceanic migrations, they likely wait to release their larvae until the whales gather in coastal areas to breed. The larvae then go through several developmental stages, which can take up to two weeks, before they’re ready to settle. “It’s not like the larva is being released from a whale and it’s going to [immediately] attach to the whale next door,” Zardus says.

When a larva is ready, a chemical signal is most likely what tips it off that it’s in the presence of whale skin. This could be a pheromone emitted by already settled adult barnacles—a strategy commonly used by other barnacle species—or it could be some molecule that wafts off the surface of the skin itself. If other barnacles are any indication, the larva probably reaches out with its sensitive antennules to familiarize itself with the epidermis. It squeezes a drop of sticky polymer out of one antennule to adhere itself temporarily, then sticks down a second antennule and releases the first one, swinging it over to another spot. By repeating this process, a larva “ends up walking around on the surface, leaving little gluey footprints,” says Zardus. “These larvae can possibly crawl all over the host until they find the right location where they want to be.”

Where they want to be is generally on the whale’s forehead, its tail, or the leading edges of its flippers. Those are the places on a whale’s body that water flows over most efficiently. That gives the barnacle a front-row seat when the whale swims through a cloud of plankton, which the barnacle also gets to eat. When the larva finds a good place to settle down, it exudes a stronger glue onto the skin and cements itself for the rest of its life, which may last about one to three years.

southern right whale

The head and “chin” of this southern right whale show rough, thick calluses called callosities. Whale barnacles, and particular types of whale “lice” (crustaceans), live within the callosities. Photo by Gabriel Rojo/Minden Pictures

Much of this is informed speculation, Zardus stresses, because living whale barnacles and their larvae are extremely hard to come by. Collecting them from a living whale is out of the question, since it would require cutting into the whale’s flesh. A dead whale that washes up has to be discovered before its barnacles die of hunger, desiccation, or predation. But even then, as Pineda discovered at WHOI, things don’t always work out. In 2005, scientists in Japan managed to harvest larvae from barnacles on a stranded humpback and nurture them for about two weeks before they died—the furthest anyone has gotten. You can source adult specimens from ancient fossil deposits or defunct whaling operations, but all of those are lifeless shells.

Some of this was on Seth Finnegan’s mind when Taylor, then his graduate student at the University of California, Berkeley, proposed doing his PhD thesis on whale barnacles. That there would be enough information in long-dead barnacles to reveal anything interesting—let alone anything about ancient marine ecosystems, which are the usual focus of Finnegan’s lab—seemed, to Finnegan, like it might be a stretch. But Taylor made enough of a plan to satisfy his adviser’s skepticism, and Finnegan signed off on the project. “Once he convinced me that it was at least worth looking into,” says Finnegan, “we began investigating.”

Taylor is about as charming an advocate as whale barnacles could hope for. He has multiple ear piercings, speaks rapturously about invertebrate adaptations, and has occasionally tweeted under the handle BarnacleBoy86. In the fall of 2015, while Taylor was casting around for a dissertation topic, one of his professors assigned a research paper about prehistoric whale populations. Finnegan, meanwhile, had suggested he read about how scientists had analyzed the chemical composition of clamshells to learn about changes in the clams’ environments.

“I literally had both of those papers sitting on my lap,” Taylor recalls, “and out of nowhere, my brain went off.” I wonder if you could do something similar with whale barnacles, he thought. Like clams, barnacles construct their shells from calcite, the most abundant natural form of calcium carbonate. They accumulate layer upon layer of calcite in their wall plates, pulling dissolved oxygen and minerals from the seawater around them. For a scientist, these layers function like tree rings, marking time as the organism grows larger. But unlike trees, which add a single woody ring per year, barnacles seem to accrete a new layer of calcite in as little as a few weeks.

fossilized whale barnacle, Coronula diadema

This fossilized whale barnacle, Coronula diadema, shows how barnacles build their shell with layers of calcite. The chemical composition of these layers can help determine where in the ocean the layer might have formed, providing clues to whale migration. Photo courtesy of Larry Taylor

Taylor did some digging and found an intriguing 40-year-old study by J. S. Killingley, then a researcher at Scripps Institution of Oceanography at the University of California San Diego. Killingley had analyzed calcite layers in the shells of gray-whale barnacles and found that their exact chemical composition depended on the water in which they formed. Unlike stationary clams, though, the barnacles had spent their lives tagging along on their hosts’ epic migrations. That meant the differences between layers represented movement, rather than conditions changing locally.

Two years later, Killingley had worked with Scripps biologist William Newman (affectionately known to colleagues as Barnacle Bill) to come up with the e = mc2 of barnacle biochemistry: an equation that relates the ratio of oxygen isotopes in a shell layer to the temperature and composition of the water it grew in. Because different parts of the ocean have unique temperature and salinity profiles, explains Taylor, measuring these isotopes could theoretically allow you to figure out roughly where in the ocean each layer had formed. “The basic idea is that there are these chemical tracers in the environment,” he says. “The barnacle puts some of those tracers in its shell and thereby keeps a kind of growing record of places that it’s been.”

Killingley and Newman had worked with modern barnacles, not fossilized ones. And because they already knew where their whales had come from, they never actually used the isotopes in a barnacle shell to reconstruct the migration of its host. But Killingley’s two obscure papers were all the encouragement that Taylor needed. With Finnegan’s blessing, he decided to hunt down some ancient whale barnacles and see what they could tell him about where they—and their whales—had gone.

The Burke Museum, on a corner of the University of Washington campus in Seattle, is the oldest and largest natural history collection in Washington State. It’s home to more than 12 million preserved fish, 20,000 bird skeletons, and 170,000 spiders in vials, as well as 40-odd whale barnacles stored in cardboard boxes, jars of fluid preservative, or latching Tupperware. The newest of the whale barnacle specimens were collected more than four decades ago. In January 2020, when I visited the museum to look at them, it was the first time they’d seen the light of day in years, according to invertebrate zoology collections manager Melissa Frey.

Frey brought the barnacles to her office and laid them out on a workbench for me to examine. They were plum-sized and ridgy, with delicate crevices and teardrop-shaped openings arranged with kaleidoscopic symmetry around their outer rims. On their undersides, calcite walls fanned out like mushroom gills to form the narrow chambers that whale skin had wedged into. Except for the ones pickled in preservative, still attached to a scrap of whale flesh, they all had empty cavities where their crustacean bodies had once been.

Taylor borrowed some modern whale barnacles from a similar collection at the California Academy of Sciences in San Francisco. A network of scientists who respond to marine mammal strandings helped him acquire several more. The San Diego Society of Natural History had half a dozen fossilized shell fragments from Pleistocene sediment deposits in Southern California. But to find the wholly intact ancient shells he wanted, Taylor knew he was going to have to look further afield.

In early 2017, Taylor, Finnegan, and two colleagues loaded up their excavation gear and flew to Panama City. They spent another day on the road to the Burica Peninsula, a coastal hangnail that straddles the border between Panama and Costa Rica. Today, the waters surrounding the peninsula are a known winter gathering spot for humpback whales that migrate to California, Alaska, and Antarctica in summer. One of the paleontologists accompanying Taylor and Finnegan had found a couple of old whale barnacles along the terraced shoreline once before.

Still, as the scientists spread out at low tide to comb the rocky beach for exposed fossils, Taylor found himself filled with anxiety. “I was afraid I’d brought these people together and used, like, thousands of dollars of grant money just for people to be disappointed,” he says. Hours later, right around sunset, Finnegan called him over to look at an interesting formation dating back perhaps 270,000 years. There, gleaming in the warm evening light, was a Coronula diadema fossil, almost perfectly preserved.

A fossil of Coronula diadema found in Panama.

A fossil of Coronula diadema found in Panama. Photo courtesy of Larry Taylor

The scientists found seven more fossilized shells and shell fragments in four days of beachcombing at Burica. They piled them into a padded bag with other specimens, then brought them back to Berkeley for Taylor to inspect more closely. An electron microscope scan revealed that the fossils’ fine structure was similar to that of the modern whale barnacles—a good sign that the ravages of time and geology hadn’t changed them too dramatically. And four of the fossils still contained uninterrupted growth records, Taylor determined, from the oldest layers on the uppermost rims of the barnacle shells to the newest ones at the base of each wall plate.

To begin to decipher a barnacle’s history, Taylor cleaned off any remaining sediment and lined up one of its six wall plates under a microscope. He used a drill bit as narrow as a human hair to extract a calcite sample about every millimeter along its side. He carefully labeled each of these microscopic shell sections and walked them over to another lab in the building for analysis. The results came, without fanfare, in an email: a table of numbers representing the oxygen isotope ratios in every layer of the shell that he had bored.

It wasn’t until Taylor started plotting the data that he knew he was onto something. Each fossil showed its own distinct pattern: isotope measurements that spiked and dipped as the barnacle stacked up shell layers during its oceanic travels. The lines on each graph took different paths in the year or so before the barnacles arrived in Panama, where they finally stopped recording when they died. The fluctuations in each barnacle shell were consistent with their cetacean chauffeurs having visited different feeding grounds—maybe, say, the Bering Sea to the north and Antarctic waters to the south—before wintering in Central America. “You saw clear evidence of migration in these fossil barnacle specimens,” says Taylor. “As a new scientist, I was like, ‘Holy shit, it works’!”

Larry Taylor in the field in Panama

Whale barnacle researcher, Larry Taylor, from the Helena College University of Montana in the field in Panama. Taylor did his PhD on fossilized whale barnacles. Photo courtesy of Larry Taylor

Other than whale barnacles, nothing else reliably recorded the month-to-month movements of ancient whales, says Taylor. Bone tissue doesn’t care about the chemistry of the water it grew in; baleen does, but it’s hardly ever fossilized. But a well-preserved whale barnacle is the perfect time-traveling tracking device. “We won’t be able to tell you, ‘This whale hung a left at Malibu,’” says Taylor, “but [we can] get a general sense of where animals might have been moving.”

Here’s why that’s cool: when in their evolutionary history baleen whales started migrating remains an open question. One hypothesis suggests that it happened around three million years ago, when massive ice sheets started spreading across much of the northern hemisphere. The colder temperatures would have frozen whales out of some of their habitats and put more constraints on where plankton could flourish in Earth’s oceans. And that would encourage the whales to start making longer and more directed journeys to seek out shelter and food. A fossilized whale barnacle is a unique window into this behavior in a whale that’s been dead for hundreds of thousands of years. Taylor’s finding is proof of concept, says Finnegan, but it also confirms that migration has been an integral part of baleen whales’ lives for a very, very long time.

Taylor and Finnegan hope to eventually analyze whale barnacles from many different time periods—including about 125,000 years ago, right in the middle of Earth’s last interglacial period. Scientific estimates put ocean temperatures from that time in roughly the same range as modern ones, and sea levels potentially up to 20 meters higher than they are today. That’s not too different from the future that we’re currently barreling into, explains Finnegan. Understanding how whales shifted their migratory patterns in response to past climate changes could theoretically give scientists a hint of what they’ll do about changes coming from here on out.

Zoom out a little more, and do a lot more scientific legwork, and the whales themselves could one day start serving as another sort of tracker. If you know where they were at any given time in Earth’s history, you can assume there were plankton there also, and the fossil record will likely confirm that. But if you knew how the whales were moving—where they wanted to be in summer versus where they wanted to be in winter—you would know something about how plankton were distributed in time, not just in space. And then, maybe, you could start figuring out how those seasonal shifts were affected by the climate, too—and that could help you understand the future of the entire ocean food web.

In 1924, the Canadian naturalist Ira E. Cornwall made careful study of humpback barnacles collected at a whaling station in Cachalot, British Columbia. He described their cask-like shape, their six-sided symmetry, and their 18 interior chambers that, given the barnacles’ freshness, were still “filled by the black skin of the whale.” He corrected a few anatomical points that Darwin’s monograph on barnacles had, in his view, characterized incorrectly. And he tried, in the restrained way that would be expected of a serious man of science, to convey a sense of urgency: “As the whales, and consequently the whale barnacles, are becoming scarcer each year, it seems advisable to describe, and figure these barnacles while they can be obtained.”

Here’s the problem with being a barnacle that lives on a particular whale species rather than rocks, shells, or crumbling old dock pilings: if your whale species goes extinct, you’re not long for this world either. A group of scientists in Europe recently raised this alarm while describing a whale barnacle fossil they found on the Mediterranean coast of Spain. Its circular outline and star-shaped array of indentations identified it as Cetopirus complanatus, a species that attaches only to right whales. Right whales don’t visit the Mediterranean today, but the Spanish whale barnacle and others have been used to make the case that, centuries or millennia ago, they did.

North Atlantic right whale

The North Atlantic right whale is one species of about a dozen that host whale barnacles. Photo by Nick Hawkins/Minden Pictures

Since then, though, right whale populations have been decimated by nearly a thousand years of whaling. Some of them have made incremental recoveries, but the North Atlantic right whale remains critically endangered, with fewer than 250 individuals left in the world. Especially concerning to whale barnacle detectives is that no one has documented Cetopirus complanatus on a living right whale for almost 170 years now—a gap no one had particularly noticed until the European scientists went looking for references. It raises the possibility that, while everyone was busy trying to save the large and charismatic right whales, one of the barnacle species that had been quietly evolving alongside them for millions of years had already disappeared.

In their 2017 paper describing the Spanish barnacle, the scientists tried one last Hail Mary. “We take advantage of this space for launching a plea to fellow naturalists interested in whale barnacles,” they wrote. “We invite all those colleagues who do fieldwork with cetaceans, those that are in charge of managing cetacean carcasses, or are interested in the biology of [symbiotic barnacles], to take note … of every whale barnacle species they are able to identify on living or dead right whales.” That would help them clarify whether Cetopirus complanatus has, in fact, become extinct—but so far, they’ve yet to receive any response.

Michael Moore doesn’t perform any necropsies these days. He now directs the Marine Mammal Center at WHOI, and after an organ transplant that left him immunosuppressed five years ago, he can’t risk exposing himself to the bodily fluids of dead whales anymore. At one point, Pineda hatched a plan to try to collect free-swimming barnacle larvae from Cape Cod Bay at the end of summer, when migrating humpbacks usually pass through. But he couldn’t, because—wouldn’t you know it—that was the year the whales didn’t even show up.

Pineda recently started wondering if he should try again one of these days. Taylor took a teaching job but is still pursuing his whale barnacle research on the side. Zardus has a custom tank for raising young barnacles all set up: it’s called a larvulator. He’s sure he could use it to raise whale barnacle larvae, too—if only he could get his hands on any live whale barnacle embryos.

For many of these scientists, whale barnacles are a passion project. What grant money there is for barnacle research often goes to engineers trying to keep them from colonizing navy ships, or to materials scientists who want to study their adhesive molecules to make medical-grade superglue. “You know, there’s never going to be an Institute of Whale Barnacle Studies,” says Finnegan. “In some ways it’s their weirdness and marginality that makes them attractive to a certain sort of person.”

Some of the whale barnacles from Cachalot ended up at the Royal British Columbia Museum (RBCM) in Victoria, where Melissa Frey worked before moving to Seattle. She remembers that specimen #A-304-00001, collected in 1923, caught her attention in particular. “I recall being intrigued by the prospects of what the whale barnacles in collections could tell us about historical distributions of whales,” she writes in an email. But as far as anyone actually trying to find out, “maybe—maybe—there was one inquiry specifically about whale barnacles during the five years that I was at the RBCM.”

Here are some other things we don’t know about whale barnacles: how did their ancestors make the leap to become hitchhikers? How did they evolve over time alongside their seafaring hosts? How much more could these portable data recorders tell us about where whales have been, and where they might be going? And what other records could they be quietly keeping—records that might help us understand the past, present, and future of our oceans, if only someone who knew how to translate them finally got a good look?