I wouldn’t be surprised if you’ve never given a second thought to the humble barnacle clinging to the rocky tideline on beaches of the Illawarra and beyond. Admittedly, until well into my adult life, I treated the creatures with mild disdain and a healthy wariness.
This attitude was honed by my experience of having knees, hands and feet shredded by their calcified carapaces while entering and exiting the water for spearfishing.
I once witnessed the skin of my brother’s foot be peeled back by a barnacle as expertly as if the ocean had taken a potato peeler to his sole. I also lived a good two years with pieces of barnacle lodged in my knee after a misplaced kick through shallow, rough water. It took that long for the bits to slowly make their way out of my skin, though a nice round scar remains– a perfect imprint of the barnacle crater. A kiss from the ocean, if you will.
But I’ve since learned that barnacles are pretty fascinating in their own right. Granted, not as fascinating as the life history of eels (that’s an internet rabbit-hole you want to be sucked into, trust me), but they have some pretty great life-history facts to contend with.
There are two main groups of barnacles.There are goose barnacles, which have a leathery ‘neck’ attaching the body of the barnacle to the substrate. You often see goose barnacles attached to flotsam washed up on the shore, and they’re actually a delicacy in several countries around the world.
The second are sessile barnacles that attach directly onto the rock or other substrate. Known by the cute name of acorn barnacles, they account for the majority of known barnacle species.
Now before I get onto acorn barnacles, I should tell you about the lesser known group of barnacles that do not have an external shell. Instead, this group of barnacles, in genus Sacculina, parasitise other crustaceans, including crabs with their soft, sack-like bodies. And if it isn't enough of an insult for an amorphous blob to be feeding off the juices of a crab while it's still alive, Sacculina barnacles engage in parasitic castration. Meaning, they attach themselves to the reproductive organs of the crustacean, rendering it sterile and preventing reproduction, which is akin to death in the natural world.
You’ll notice I said these barnacles parasitise other crustaceans: that is because barnacles are not molluscs, as their shells would suggest. They are crustaceans, related to crabs and prawns.
And now back to acorn barnacles. My absolute favourite fact about these creatures is due to my juvenile sense of humour: acorn barnacles have infamously long penises. Up to 10 times their body size! So long, in fact, that they use that considerable length to impregnate adjacent females within their penile range. The best part, in my opinion, is that the penis dissolves at the end of the mating season and then regrows for the following year. What a skill!
To further prove their reproductive prowess, most acorn barnacles are hermaphroditic, meaning they possess both male and female reproductive organs. So, if no other barnacles are within reach of their long-range missiles, they simply clone themselves through self-fertilisation. This is especially handy since they are permanently stuck to whatever surface they adhered to as juveniles. Even after the crustacean inside dies, the shell remains attached, virtually indestructible. Well, my knees would attest to that anyway.
But how do they get there in the first place? Barnacles begin their lives with a short stint as free-floating planktonic larvae before adhering to a hard surface. This surface can be anything from the hull of a boat to a turtle’s shell but most commonly it's intertidal rocks.
When it’s time to settle down and find a permanent place of habitation, the barnacle uses its head and the cement glands in the antennae to glue itself to the surface. From there, it metamorphoses into a juvenile barnacle that looks just a miniature version of the real deal. From there, each barnacle begins building its shell-home.
The architecture of each shell is roughly the same. The prerequisites for barnacle shell construction, as stipulated by the Barnacle Building Board, are as follows: must be tough as nails, tough enough to gouge human feet and remain long after tenant perishes; and construction must include a trapdoor.
The trapdoor serves as the barnacle’s connection to the outer world. When the tide is out and the barnacle is exposed to the air, the protective door remains closed against the possibility of desiccation. When the tide is high and the barnacle is in contact with the water, it unfurls its feathery legs to catch and feast on plankton and detritus floating by.
My interest in barnacles comes from an aesthetic standpoint too – they can be very beautiful, like the cluster of pink acorn barnacles pictured, found in Wollongong.
Not so boring after all!
My hope is that next time you step on a barnacle, you'll pause, not just to swear at it but also maybe to give a nod of appreciation… thumbs up? Finger guns? Okay, I won’t judge if you still just swear and glare.
