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Dive Dry with Dr. Bill

#353: The Barnacle Billy Buffet

Barnacles are one of Nature's skid proof surfaces. If you've ever hiked along the intertidal to search through tidepools, you've probably taken advantage of these tiny, hard-shelled critters to ensure stable footing on the normally slick rocks. However, should you slip and fall, barnacles suddenly turn into tools of torture as they penetrate your skin leaving bleeding cuts in several places. I've even had them do a good job of shredding a wetsuit or two when the surge has propelled me into a subtidal wall covered with them. Of course most of my wetsuits are already well shredded thanks to the numerous "shark attacks" I've survived (just teasing).

Although many think barnacles may be related to snails based on their appearance, they are actually crustaceans related to shrimp, crab and lobster. I'm going to focus on one group of barnacles commonly referred to as acorn barnacles. These are the ones most commonly seen on the intertidal and, when exposed at low tide, subtidal rocks. Barnacles have cone or volcano shaped shells firmly cemented to the rocky substrate. Scientists have studied the natural adhesives they secrete in a search for new products to buy at Chet's Hardware (or Home Depot for those of you living on "The Big Island" across the Channel).

If you look through the center of the hole on top, you will normally see two plates or valves that are usually tightly closed when the barnacle is exposed to air. These valves provide a water- and air-resistant seal to keep moisture inside the shell and prevent the crustacean from becoming dehydrated. Of course if they remained hermetically sealed inside, how could they feed? When the "tide rushes in and plants a kiss on the shore," the barnacles open up their valves and extend a series of seemingly furry feet. These appendages, sometimes referred to as cirri, sweep through the water column to capture plankton and organic matter for the barnacle to munch on. In fact, barnacles belong to the biological subclass Cirripedia which means "feathery foot."

Now you might ask, how does a barnacle stick its feet out of the hole on the top of the shell? Doesn't that mean they are actually standing on their heads... just like good old Cal Worthington? Actually that is indeed the case! It doesn't give YOU a better deal, but it does help them feed. When a barnacle settles on the rock, it attaches by its head and builds the shell to protect it. They are then able to extend their several "feet" out side it and kick in the food.

Since I've covered munching, I really should touch on the other "M" word, mating. However, I'll try not to get too explicit about this highly unusual group of species since children may be reading this column (shouldn't they be in school now?). Because barnacles are cemented to the bottom, they cannot move about in search of a mate. In fact, they are usually hermaphrodites, either alternating between "maleness" and "femaleness" or being both at the same time. The "males" are faced with a difficult challenge. Adjacent females may be some distance away, making the conjugal act not an easy task. To succeed at this basic and very necessary function, male barnacles have developed... uh, reproductive structures... that may be eight times as long as their bodies. Now who says size doesn't matter? Sorry to any sensitive readers, but Steinbeck and I have repeatedly stated that biologists tend to be libidinous, licentious, lubricious and lascivious folks (look those up in Word Power Made Easy if it's still in print).

We'll leave the rest up to your imagination before I get censored. Fertilized barnacle eggs hatch into larval forms that drift with the plankton. They feed and grow as they wander, dispersing to new habitats to colonize them and contributing new genetic material to any existing population they may settle in. Barnacles can detect appropriate places to settle through chemicals released by other members of their species, or possibly by the substrate itself. You've never seen a barnacle on sand or silt... but of course they do colonize the skin of gray whales

If you haven't put a fresh coat of bottom paint on your boat, its hull may become their new home. I remember back in the early 1970s my Harvard roommate, then a Navy ensign, was visiting Toyon with his wife. We were having a great time reminiscing when the wife looked at their boat tickets and realized it was leaving two hours earlier than they thought. We jumped into my old yellow dory ("Eleutheria" which later became Barney's Banana Boat and finally Boppo the Clown's before finally sinking for the last time). When I cast off the boat to head towards town, it kept going in circles. I looked down over the transom to see a huge mass of barnacles forming a gargantuan ball on the prop. Fortunately the Toyon School's K-V was nearby and I got them to the boat on time.

Locally we have several species of acorn barnacles. Common names have included the giant, thatched and buckshot barnacle. You can see them on the Pleasure Pier pilings, the rocks at Casino groyne, the concrete of Cabrillo Mole... and, of course, the hulls of boats in the harbor unless Paul has cleaned them already. When the gray whales visit our waters, they bring with them barnacles attached to their skin.

Barnacles played an important role in several of my biology classes at Toyon. When a group of young ladies from Denver's Kent School came out to study marine biology (and test out the idea of coeducation) in the early 1970s, I had a lab exercise they referred to as the "idiot's delight." Teams of students had to count all the barnacles in three inch square holes cut out of cardboard in three areas within their distribution. Although a tedious exercise, it did show that barnacles were most dense in the middle part of their range and tapered off in the direction of both higher and lower tide. At the lower end they were limited by predators and competition for space with other intertidal life. Higher up in the intertidal they were limited by a lack of moisture and shorter immersion times during which to feed.

Another humorous Tale of Toyon involving barnacles was my annual "survival hike." Remember, these were the days of the late 60s and early 70s when organic living was very fashionable. I would hike with my students to Little Harbor, where each was expected to gather natural foods and make a meal (in the days before the Conservancy was formed of course). I would make a stew out of barnacles (the animals, not the shells), limpets, cactus and seaweed. How did it taste? Well, not like chicken... more like all the other inedible meals I make. Not one of my students ever requested my "secret recipe" (and Duke never tried to sell it to competitors either). Of course unknown to me, several of my students would stop for a burger or a steak at the Airport-in-the-Sky before arriving at our campsite "not hungry." Grrr.

© 2009 Dr. Bill Bushing. Watch the "Dive Dry with Dr. Bill" underwater videos on Catalina Cable TV channel 49, 10:00 AM and 5:00 PM weekdays and on Charter Communications Cable channel 33 at 7:30 PM on Tuesdays in the Riverside/Norco area. Please help me climb out of self-imposed poverty... buy my DVD's (see this link). Yes, take Dr. Bill home with you... we'll both be glad you did!

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Buckshot barnacles ready to count (601, 602, 905...), thatched barnacle showing two valves on right;
acorn barnacles extended "feathery" feet to feed, barnacle larva from plankton.


Decided to add another set of images that I took through my microscope yesterday. These show the cirri or feeding feet,
the shell with two valves seen through the hole, and two images of the valvces used to keep the barnacle moist during low tide.

This document maintained by Dr. Bill Bushing.
Material and images © 2009 Star Thrower Educational Multimedia