Barnacle Castles

Poulsbo, WA – This time of year, we love to take advantage of the daily low tides, a time when the sea rolls back her foamy, wet quilt for a few hours and we can examine the busy world of the intertidal zone. It is the diverse area of beach that is regularly exposed and lies between the high low tide marks. The creatures of the intertidal zone are one tough bunch of seasoned over comers as each species aggressively defends its favorite place to hang out or hang on as the case may be.

One of the most common creatures in the intertidal zone has claimed the upper reaches, the ruthless, seemingly barren place most exposed to changes in temperature, moisture and salinity, but also farthest from would-be marine predators. It is in the path we terrestrials use to clamber down to the water’s edge, crunching and cracking as we go. Unfortunately, the crunchy sound effects come from our shoes breaking the exterior plates of today’s marine wonder… the rugged barnacle.

cropped-cropped-img_95551.jpgThere are over 1,400 species of barnacles currently known, and the Pacific Northwest hosts six main varieties. They are common and abundant in the intertidal zone, easy to track and observe even when the tide is high. They are filter feeders, pulling in drifting plankton, but they themselves are also an important food source in the intertidal zone. Marine worms, snails, sea stars, as well as some fish and shorebirds will eat barnacle, although the barnacle’s armored exterior often forces predators to sing for their supper.

Zoologist Louis Agassiz once said a barnacle is “nothing more than a little shrimp-like animal, standing on its head in a limestone house and kicking food into its mouth.” It is a funny visual, but is also a good way to remember the unusual anatomy found in the barnacle family. After they hatch, barnacle larvae float as drifting plankton searching for a suitable place to settle down and build their own calcium castles. Interestingly, adult barnacles secrete compounds to attract the tiny larvae to their castle compound. Once a suitable building site is selected, a young barnacle literally glue its head to the spot with a tenacious monster glue and begin construction of its very own castle.

Barnacle glue is so strong that it usually remains long after the barnacle that built it is gone. Dentists are intrigued with its holding power.

During low tides, we see thousands of them dotting the rocky “shorescape” like little white castles, each fortified with five to six rock hard plates that form sturdy walls and another four plates that create an impenetrable door. If you are able to observe barnacles submerged in pools or channels of incoming water, you are in for a somewhat comical treat, as a muscle guard opens the castle door for the important business of royal feasting.

Six pairs of little feathered “feet”(cirri) emerge to begin their repetitive waving and swatting through the plankton rich water to pick up lunch – a drive-through experience in reverse. It truly is a wonder to watch, especially when you know their remarkable background story.

Unusual design lies in even the most common of creatures, so be sure to include them as you track wonder.

Acorn Barnacle - Rockaway Beach
Acorn Barnacles are the most common barnacle on our shores and can be identified by their diamond-shaped opening and wavy outer plates. They grow in very tight spaces so when there is not room to expand out, they expand up, so often look elongated.
Haystack Barnacles have little vertical spiny projections that look like hay stacked in a field after a harvest. The inner plates come together to look like a beak. This example is pretty crusty, but look at the base to see a few vertical growth lines.
The Giant Barnacle looks like a giant cup with a bottom and sides. It lives in deeper water, so it is very rare to find a live one exposed in the intertidal zone of bays and inlets. It prefers areas where water is rushing past.  Most of the larger barnacles found on the beach are Haystack Barnacles, not Giant Acorn Barnacles.
Leaf Barnacles (also called Goose or Goose-Necked) feeding with their feathery leg-like cirri. Theses cool looking barnacles remind me of reptile toes and are commonly found on the open coast where water moves fast.
Common Goose Barnacle is different from the others in that it attaches to drifting objects like wood, buoys, bottles and even the shell of the Purple Sea Snail where the larvae were once attracted to the shady underside of the object. The stalk is long, thick rubbery and flexible. The barnacle itself if enclosed in 5 yellow/orange edged white plates. Find them washed up on the west coast beaches clinging tenaciously to beached objects.

Little Brown Barnacles can be identified by the small oval opening and little cross seen across the oval. (not pictured yet)

Crenate Barnacles have very smooth white outer plates. (not pictured yet)

WT LogoCultivate Wonder… Discover Design

Where and When – Barnacles are very easy to find all year-long on any beach with stable surfaces such as big rocks, pilings, etc. Acorn Barnacles are the most commonly seen in the upper intertidal zone, along with Little Brown and Haystack Barnacles. Giant Barnacles live deeper down and are rarely seen alive from the beach, although you may find an empty “castle” washed up on the beach. Gooseneck Barnacles are the most rare and unusual in the Salish Sea. They can be found where there is a strong current so be aware of wave action when you see them.

Barnacle shells are as tough as nails, but even they have a breaking point.  When you are on the beach or climbing over the rocks, be careful where you step. The crunching you hear is most often the sound of barnacles shells breaking or chipping. When possible, use sandy areas to walk. In the intertidal zone, you will not be able to avoid stepping on barnacle shells, but find try to walk carefully over barnacles without stomping or deliberately stepping on shells.

Wonder Triggers for Young Trackers

  • Find a group of barnacles growing together. Study how they fit together. Is there something in their design that helps them fit so many in a small area?
  • Study one larger barnacle.  Can you see the outer plates that form the walls of the “castle?” Can you find the little door that seals shut when the water recedes? What patterns do you see in the door plates? Some barnacle have inner plates that form a cross, while others look like the letter W. Can you think of other ways to describe the inner plates of different barnacles?
  • Touch the barnacles to see how they glued securely. Find a spot on a rock where a barnacle has fallen off and see if you can scratch off the glue. Barnacle “glue” is amazing because it can hold up in and out of salty water for a long time. Dentists are studying it to learn about stronger glues for dentistry. Can you think of other ways barnacle glue might be helpful?
  • If you are in a place where the water is rushing past the barnacles, watch them open their inner plates and extend their cirri to comb the water for things to eat. Do the barnacles move slowly or quickly? Do the cirri go in and out of the barnacle’s body or stay extended? Where do you think the mouth is?

References and Resources

Oregon Coast Aquarium

National Oceanic and Atmospheric Administration

The Wild Classroom – Intertidal Zone

Bay Nature – How do Barnacles Make Baby Barnacles?

Monterey Bay Aquarium – Barnacles

Images – Sharon Pegany, Copyright 2018

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