OF BARNACLES AND BOTTOM PAINT

BARNACLES

Boat owners see barnacles much the same way backyard birders view squirrels or the way gardeners feel about any number of small mammals that gnaw on fresh veggies: They don’t much like them.

And like feeding birds or growing vegetables entails battling with these respective pests daily and often to no avail, boat owners’ efforts to mitigate barnacles (and the other flora and fauna collectively known as “marine fouling”) is ongoing and often feels futile. Yet while rodents and lagomorphs may have a certain charm in a different context (animated films, Beatrix Potter books, internet memes, etc.), barnacles are almost universally undervalued. (Apparently “Barnacles!” is used as a stand-in expletive on the animated TV show SpongeBob SquarePants.) Even in tide pools and aquarium touch tanks, the barnacle can’t compete. It lacks the star power of the sea star, and even common hermit crabs (they steal other animals’ shells!), the drab green rockweed (you can pretend it’s mermaid hair!), and timid periwinkles (they’re not as boring as barnacles!) have more allure.

The largely inert barnacle seems to barely qualify as an animal. And it likely doesn’t help that the one “amazing science fact” about the barnacle—the relative size of one of its organs—is not well suited for kids’ books, and so the barnacle is largely ignored in the “nature is cool” literature that has an outsize impact on wildlife popularity.

This is not to say that no one likes barnacles. Some people love them. In fact, many of the people who know the most about barnacles—biologists—have been obsessed with these creatures for years. In the middle of publishing his best-known research on evolution, Charles Darwin essentially spent eight years nerding out on barnacles, attempting to classify these enigmatic organisms. His deep dive into the species he called Cirripedia was inspired by his observation of a barnacle on his research vessel, HMS Beagle, years earlier, a burrowing barnacle that Darwin, no joke, had named “Mr. Arthrobalanus.”

Biologist Rachel Carson was also fascinated by barnacles. And both Darwin and Carson had their barnacle-related work overshadowed by the game-changing nature of their later works. In The Rocky Coast, one of her pre– Silent Spring books, Carson spends much time pondering the barnacle, introducing the species with this poetic description: “Like drifts of old snow no longer white, barnacles come into view; they blanket rocks and old spars wedged into rock crevices, and their sharp cones are sprinkled over empty mussel shells and lobster-pot buoys and the hard stipes of deep-water seaweeds, all mingled in the flotsam of the tide.” And they don’t just provide for scenic shorescapes. Carson characterizes these barnacles as pioneers—humble creatures that likely made way for all the other life forms to settle on the inhospitable rocky coastline of northern New England. She writes, “The first permanent inhabitants must have been such plankton-strainers as the barnacles and mussels, who require little but a firm place to which they may attach themselves.”

And most boat owners would likely ask these barnacles, of all the firm places in the ocean, why must you attach yourself to my hull?

BOTTOM PAINT

As long as naturalists have been fascinated by barnacles, boaters have been frustrated by them. Even Darwin, after his eight-year obsession, ultimately found himself exasperated by the barnacle and its refusal to fit neatly into any taxonomic system. In a letter to a friend in 1854 he wrote, “I hate a Barnacle as no man ever did before, not even a sailor in a slow-sailing ship.”

Throughout history, sailors have tried just about everything to discourage growth on the bottoms of their ships. Unfortunately, though perhaps not surprisingly, the literature on this history of antifouling solutions is limited. But in the mid-1940s, the U.S. Navy commissioned a study by the Woods Hole Oceanographic Institute. The resulting monograph published in 1952, Marine Fouling and Its Prevention, is a very thorough scientific examination of every aspect of the topic that could well be considered the Origin of Species/Silent Spring of the biofouling canon. A chapter titled “The Fouling Community” runs through the more than 2,000 species that might attach themselves to a ship’s bottom, and in

“The Principal Fouling Organisms” barnacles get a shout-out as “the most familiar of the arthropods found on ship bottoms.”

And in the report’s chapter called “The History of the Prevention of Fouling” there’s another dubious shout-out, this time to Darwin himself. The previous science on antifouling had been scarce, the authors note. Up to that point only one “real” scientist, Sir Humphry Davy, had done a truly rigorous study of various compounds’ effectiveness in preventing unwanted marine growth. The authors continue: “It is interesting to note in passing that a generation later another great English scientist, Charles Darwin, became the authority on barnacles and thus contributed valuable knowledge of the subject without apparently becoming concerned with its practical aspects.” (Apparently his empathy with the “sailor in the slow-sailing ship” did not compel him to seek a solution.)

But there were many others more directly affected by these slow-sailing ships who were driven to find a better way to protect boats from barnacles, et al. The Navy’s antifouling report provides this succinct recap of the evolution of their solutions: First, ships use metal sheathing to prevent growth, and copper is finally identified as the most effective antifouling agent. But then as iron ships replace wooden boats, copper sheathing can no longer be used as it causes electrolytic corrosion of the metal hull. Finally, the invention of coppercontaining bottom paints allows copper to be used on top of an anticorrosive hull coating.

Though this history spans centuries, these three distinct eras occurred in somewhat rapid succession. Various metals, including lead and copper, were likely used on ships as far back as the Greeks and Romans, but the first documented use of copper sheathing on a hull was in the 18th century. Iron ships began to be built in the 1830s, and the third antifouling era, the use of copper-based bottom paint, was ushered in the mid-19th century. The first factory to produce a copper bottom paint, the Tarr and Wonson Paint Factory on Rocky Neck in Gloucester, Massachusetts, filed their patent for “Improvements in Paints for Ships’ Bottoms” in 1863.

But the history of antifouling unfortunately did not end there. Shortly after the report’s publication in 1952, a new biocide, tributyltin (TBT), was introduced and began to be used widely in bottom paint in the 1960s. The marine equivalent of Carson’s main target, the pesticide DDT, TBT was a harsh poison that caused significant problems in the marine environment, including severe deformities in many shellfish species. Carson passed away in 1964, and it’s hard not to wonder whether the Environmental Protection Agency’s 1988 ban would have been hastened had she been alive. It seems only natural that she would have taken up the cause on behalf of her beloved tide-pool dwellers.

With TBT off the table, most boat owners turned back to copper-based paints, which remain common today. Now, it can be hard to pinpoint the main culprit of rising copper levels in ocean water (industrial pollution from factory runoff and mining operations, for example, is a major source). But it’s hard to argue that large numbers of boats coated in paints that work by leaching small amounts of a substance is not at least partially to blame for the increase in concentration of that substance, especially in densely packed marinas and crowded harbors. In 2011, Washington became the first state to enact a ban on copper-containing bottom paints, perhaps not surprising given that copper toxicity is particularly harmful to salmon.

BIOMIMICRY

Though the debate continues about copper bottom paints, what’s clear is that continuing to rely on biocides of any type is not sustainable. Fortunately real progress in the search for an environmentally friendly antifouling agent is being made in the study of biomimicry: looking to nature for inspiration in solving engineering challenges and environmental problems. For example, the fact that sharks generally do not attract barnacles or algal growth has led scientists to develop sharkskin-inspired coatings that not only have use on ships but have also been studied in medical settings as a way to discourage microbial growth on working surfaces.

Taking cues from an entirely different ecosystem, researchers in Australia have developed antifouling coatings made up of

“nanowrinkles” (truly microscopic structures) that mimic the leaves of the carnivorous pitcher plant and create a slippery surface that barnacles and other members of the “fouling community” cannot attach to. The advances in technology that allow these researchers to mine the nanostructures of plants and animals for inspiration are also allowing today’s scientists to uncover the secrets of the enigmatic barnacle in a way Darwin could have only dreamed of.

BARNACLES (PART II)

Underneath its crusty exterior, the barnacle is actually a fascinating creature, and one that produces one of the strongest bioadhesives—a cement that puts your 5200 to shame. (According to NOAA, the tensile strength of barnacle glue is 5,000 psi. A tube of 3M’s strongest marine adhesive sealant has a tensile strength of only 700psi.)

While scientists have long known that barnacle cement is a two-part solution, they had long assumed it worked much like a two-part epoxy: mix first to activate the adhesive. But that didn’t explain how the barnacle was able to use this adhesive so effectively underwater. In a 2014 article in Nature Communications, a team of researchers shared the results of a groundbreaking study. With improved photon technology, they were able to, for the first time, observe barnacle larvae attaching to a rock in high enough resolution as to see that the two-part adhesive was not mixed but rather used simultaneously—a lipid-based substance moves the water molecules out of the way while the other, a photoprotein, adheres to the surface.

The benefits of this research are two-fold. As the researchers put it, “Knowledge of the lipidic contribution will hopefully inspire development of novel synthetic bioadhesives and environmentally benign antifouling coatings.” In other words, not only can the barnacle teach us how to make a bombproof glue, but in learning how barnacles actually attach themselves to surfaces so stubbornly, we might also be able to do better job of preventing them from doing so—without polluting our oceans.

BOTTOM PAINT (PART II)

In a fitting second life, the pioneering antifouling paint producers, the Tarr and Wonson Paint Factory, which closed in 1980, was recently renovated and now serves as the home of Ocean Alliance, a nonprofit organization sponsoring oceanographic research. The Ocean Alliance uses drones to study whales, and perhaps there is something we can learn from the whale—specifically, how to live with barnacles.

Barnacles have a type of symbiotic relationship with whales—it’s called commensalism. The relationship is not mutually beneficial. But it’s not a parasitic relationship either; for the most part, the whale is not harmed by the barnacles that live on it. (It takes upward of 1,000 pounds of barnacles on an average humpback whale before it experiences drag!)

Maybe this type of symbiosis is what boaters can aspire to. And maybe the barnacles themselves will show us the way to this peaceful, if slightly lopsided, coexistence. Or maybe the relationship could be one of true mutualism, albeit a bit indirect. In exchange for the wisdom of the barnacle—a nontoxic dental cement, a better epoxy—the boat owner provides it a home.

But for now, there’s bottom paint.