Barnacles are fascinating and often unappreciated

Probably few people exploring the intertidal zones of local beaches pay much attention to barnacles.

By Barbara Julien

Probably few people exploring the intertidal zones of local beaches pay much attention to barnacles. Grey, crusty, unexciting at first glance, they tend to be ignored as we crunch over them on rocks while looking for the more colourful starfish and flower-like anemones.

Yet cirripedia are fascinating and under-appreciated animals, carpeting inorganic rock with a seething mass of life.

They are named for the feathery food-capturing appendage — the cirra, which means “curled” in Latin -— which waves above the openings of their plated conical shells.

This appendage looks like a tongue but is actually made of six pairs of spine-covered legs. In adulthood, the creature is attached to the rock it lives on (or the pilings or the whale) by a glycoproteinous membrane secreted by “cement glands” on top of its head.

Its mouth is in the middle of its body, and although it contains blood it has no heart, yet has a sensitive nervous system reacting minutely to light and shadow, water and desiccation.

Two plates will close over its aperture in response to environmental variations, and as it grows the shape of the shell even within a single species will vary in response to erosion by water and water-born particulates, making species classification difficult.

A type of crustacean (related to crabs and lobsters), barnacles are divided into “acorn” and “peduncular” types. The most common species found on Victoria’s shoreline is Balanus cariosus which is of the acorn group, but species can be hard to distinguish without dissection, specialized knowledge, and a magnifying glass with which to examine such details as mouth parts, or the spines on the sixth leg.

Barnacles, then, are not the empty toothy-looking shell we see at first glance.

Under their plated chitinous coverings are porous “walls” and skin, through which they absorb oxygen.

Their lifecycle is surprisingly colourful, to the initiated. As it matures, a larval barnacle moults, casting off and re-growing the walls and skin. Free swimming at first, in its final larval stage it attaches to a surface head-first, after emitting its protein-ous glue.

Barnacles are hermaphroditic, in that all individuals carry egg sacs, ovaries and testes. Self-fertilization however is rare. So how is reproduction accomplished between crusty walled individuals stuck immobilized on rocks and boat hulls?

One method is “sperm casting,” by which some absorb sperm ejected by others into the water, in a way perhaps analogous to their method of feeding by passively scooping up plankton. Another tactic was the evolution of, proportionately, the longest male organ in the animal world — the only organ that ever leaves the shell of the sessile adult barnacle and extends toward its closest neighbours.

Limpets and mussels compete with acorn barnacles for space, and mussels, whelks and some starfish prey on them.

If we try to walk barefoot on a barnacle-strewn beach we surmise that their jagged openings are protection against other forms of danger.

The acorn barnacle is not edible to humans, but the gooseneck is. This is one of the pedunculate group of species which have a “capitulum” at the end of a muscular stem (the peduncle) whose base cements to rock. Goosenecks occur around Clayoquot Sound where they are the only barnacles in North America legally harvested for food.

Barnacles, being neither threatened with extinction nor particularly photogenic, are commonly ignored, but they have their own beauty.

Anyone walking on the rocks below the Dallas Road cliffs may notice in tide pools lit up by sunlight, the dreamy balletic sway of cirra delicately waving in unison just under the water.

Barnacles have adapted to bioregions all over the globe and fit snugly and unassumingly into our own.

They’re not just empty shell on rock: even the most unprepossessing creatures possess hidden depths, if we look.

 

 

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