Topsy-turvy life of the North Island barnacle

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Special thanks to Publisher of The North Island Eagle, Kathy O’Reilly
Originally printed Friday, August 10th in The North Island Eagle 

Ouch!  A little cut on your foot appears as you walk across the rock covered beach. You carefully dance from rock to rock avoiding the sharp pointy tops of the creature responsible. You are reminded that you have seen them on wharf pilings; you have seen them invading the bottom of every West Coast boat; you have even seen them attached to whales!

Last month we launched the summer tidal pool series of articles. We began with beach art and trapped mermaids. I received a request to write some sea facts on a prevalent but often underappreciated ocean annoyer. This week we take a quick look at a creature which causes us more frustration than comfort; a close relative of crabs and lobsters – the barnacle.  

The barnacle is an arthropod (meaning it has an exoskeleton, jointed appendages, and segmented body). Other types of arthropods include insects and crabs. A barnacle is related to insects and crabs? Yep! Lobsters, crabs, and sand fleas are closely related. A barnacle is actually a crustacean.

There are over 1, 000 species of barnacles, with one of the most common (and the most likely you will encounter) referred to as the “acorn” barnacle. Although there is a type of barnacle that is “naked” (meaning it has no outer protection) and also a barnacle that burrows, the barnacles we see here in BC (like the acorn barnacle) are almost always covered by a hard outer shell made from calcite secretions (a white calcium carbonate substance secreted by the animal to make a protective shell).  

The top of an acorn barnacle is called an operculum (a part of the animal’s structure that opens and closes or forms a “lid”). When this top opens a feathery long plume extends for feeding on plankton and algae. This style of feeding is usually referred to as “suspension feeding” or “filter feeding” And now it gets weird. That operculum “top” we just talked about? Well, it’s not really the top at all. The barnacle is actually upside down and attaching itself with its forehead! A cement gland forehead! And those feathery plumes? Well, they are called “cirri” and technically speaking they are the feet. Yes, a barnacle eats with its feet! And, wait for it, it breathes through them as well! That’s right, no nose. It does not have a heart either.

So, quick re-cap, we have a heartless animal that is attached upside down with cement glands to whatever it wants and then opens up its bottom to eat and breathe with its feet? Yep, a truly upside down situation. Which brings me to my next factoid; barnacles are actually quite a complex marine animal. Unlike other crustaceans that are either male or female, barnacles are hermaphrodites (meaning they contain both sexes). They reproduce through cross fertilization. A baby barnacle is a small larva that sort of looks like a one eyed shrimp which swims around until it finds a suitable spot to settle down and grow (usually by other barnacles not far away).

Well, folks, there you have it. As you explore the tidal pools this summer, or clean your boat, docks, and pilings, remember that “top” isn’t a top at all but rather the bottom of a unique upside down filter feeding crustacean.

Bryce Casavant is a former BC Conservation Officer and Doctoral Candidate with Royal Roads University. He writes for the Eagle from his home on Vancouver Island. 

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