DIVE DRY WITH DR. BILL #784: FEATHER FEET
A while back I wrote about a field laboratory exercise I created for my marine ecology students back in the early 1970s. It involved counting the number of barnacles within a square template to determine population density at various points in their distribution along the shore. Some of my students called it the "Idiot's Delight" lab.
After writing that column, I realized that many of my readers might not know much about barnacles. Some are found too high in the intertidal zone to be commonly seen by divers. Often those of us who do descend into the briny deep curse them when waves or currents dash us against the rocks where barnacles often cause cuts and bruises.
Barnacles are a type of crustacean classified in the phylum Arthropoda. Critters in this phylum are grouped together based on their hard exoskeletons, jointed bodies and paired appendages. Other members of the phylum include lobster, shrimp and crabs. Land-based arthropods include the insects and spiders. Barnacles are classified in the subgroup Cirripedia which translates to "curl or feather feet." I used to be light on my feet and danced like a feather, but they wouldn't admit me to this class. There are an estimated 1,200 species of barnacles.
The members are often divided into acorn or goose-neck barnacles although there are several other types. Acorn barnacles have a classic look that most casual observers will recognize. Their calcium carbonate shells are attached directly to rock or other hard substrate, and are sealed with several plates known as valves. When the barnacle settles out of the plankton, it uses a cement gland to attach itself to the substrate by its head or back. Then it secretes the hard shell around it to protect it from dessication when exposed to the sun or predators when submerged.
Gooseneck barnacles look quite different and are attached to the substrate by a fleshy "neck." Their shells do not protect them from dessication as well as those of acorn barnacles so they are usually found in the lower intertidal or subtidal.
Some barnacles readily attach to drifting material such as logs or giant kelp rafts. They generally feed out in open waters. A few species of barnacle are free living in the open ocean. Another group attaches itself to the bodies of whales and cruises the ocean during the whale's migration. Gray and humpback whales are two local species on which these barnacles may be seen. Others are even parasitic, usually living in crab hosts.
Barnacles are filter feeders. They extend their feathery "feet" (called cirri) outside the confines of the protective shell and constantly sweep the surrounding water to capture yummy plankton. Of course barnacles in the intertidal can only feed while they are submerged as there isn't any plankton in the air! Other groups are submerged most of the time and can feed at will.
WARNING: Parents of young children should stop reading this column to your kids since I'm about to enter the world of sex. Yep, barnacle reproduction! Critical to maintain any species. Since barnacles are cemented to the substrate and encased in thick shells, they can't go out and roam the bars at night in search of a life partner. Of course that hasn't worked for me, either! Most barnacles are hermaphrodites and have both "male" and "female" sex organs. However they are generally unable to fertilize their own eggs.
There are two primary methods for creating a next generation. One is known as sperm casting. "Males" release their sperm into the surrounding water and the "ladies" try to play catch, and hopefully capture enough to fertilize their eggs. Sometimes this is only slightly more effective than the lottery. The other method is for the male to extend its penis out of its shell and enter the shell of a "female" to better ensure fertilization. It is said that a barnacle's penis is larger relative to its body size than that of any other animal.
The fertilized eggs develop into a larval form known as a nauplius. In this stage it may undergo several molts while living in the plankton for periods of up to half a year. Just before it is ready to settle down and raise a family of its own, the nauplius transforms into a cyprid larva. The cyprid does not feed. It's primary purpose is to sense potential sites to settle down on. It may assess various characteristics of the substrate such as texture, geology, chemistry and how damp it is.
Barnacles are actually considered delicacies in countries like Japan, Spain, Portugal and Chile. Way back in the 1970s I made a barnacle and limpet stew while on a survival hike to Little Harbor with my students. I survived it... just like I have the rest of my culinary attempts. I must have a cast iron stomach. Scientists are also interested in studying the very strong cement barnacles use to attach to rocks. They are hoping to synthesize it and market it commercially. I wish they had succeeded much earlier. If so, they might have discovered the secret to removing all the barnacles from the hull of my old boat!
© 2018 Dr. Bill Bushing. For the entire archived set of over 750 "Dive Dry" columns, visit my website Star Thrower Educational Multimedia (S.T.E.M.) Home Page
Image caption: Thatched acorn barnacles and gooseneck barnacles; barnacles on gray whale's head and nauplius larva (courtesy of Wikipedia).
A while back I wrote about a field laboratory exercise I created for my marine ecology students back in the early 1970s. It involved counting the number of barnacles within a square template to determine population density at various points in their distribution along the shore. Some of my students called it the "Idiot's Delight" lab.
After writing that column, I realized that many of my readers might not know much about barnacles. Some are found too high in the intertidal zone to be commonly seen by divers. Often those of us who do descend into the briny deep curse them when waves or currents dash us against the rocks where barnacles often cause cuts and bruises.
Barnacles are a type of crustacean classified in the phylum Arthropoda. Critters in this phylum are grouped together based on their hard exoskeletons, jointed bodies and paired appendages. Other members of the phylum include lobster, shrimp and crabs. Land-based arthropods include the insects and spiders. Barnacles are classified in the subgroup Cirripedia which translates to "curl or feather feet." I used to be light on my feet and danced like a feather, but they wouldn't admit me to this class. There are an estimated 1,200 species of barnacles.
The members are often divided into acorn or goose-neck barnacles although there are several other types. Acorn barnacles have a classic look that most casual observers will recognize. Their calcium carbonate shells are attached directly to rock or other hard substrate, and are sealed with several plates known as valves. When the barnacle settles out of the plankton, it uses a cement gland to attach itself to the substrate by its head or back. Then it secretes the hard shell around it to protect it from dessication when exposed to the sun or predators when submerged.
Gooseneck barnacles look quite different and are attached to the substrate by a fleshy "neck." Their shells do not protect them from dessication as well as those of acorn barnacles so they are usually found in the lower intertidal or subtidal.
Some barnacles readily attach to drifting material such as logs or giant kelp rafts. They generally feed out in open waters. A few species of barnacle are free living in the open ocean. Another group attaches itself to the bodies of whales and cruises the ocean during the whale's migration. Gray and humpback whales are two local species on which these barnacles may be seen. Others are even parasitic, usually living in crab hosts.
Barnacles are filter feeders. They extend their feathery "feet" (called cirri) outside the confines of the protective shell and constantly sweep the surrounding water to capture yummy plankton. Of course barnacles in the intertidal can only feed while they are submerged as there isn't any plankton in the air! Other groups are submerged most of the time and can feed at will.
WARNING: Parents of young children should stop reading this column to your kids since I'm about to enter the world of sex. Yep, barnacle reproduction! Critical to maintain any species. Since barnacles are cemented to the substrate and encased in thick shells, they can't go out and roam the bars at night in search of a life partner. Of course that hasn't worked for me, either! Most barnacles are hermaphrodites and have both "male" and "female" sex organs. However they are generally unable to fertilize their own eggs.
There are two primary methods for creating a next generation. One is known as sperm casting. "Males" release their sperm into the surrounding water and the "ladies" try to play catch, and hopefully capture enough to fertilize their eggs. Sometimes this is only slightly more effective than the lottery. The other method is for the male to extend its penis out of its shell and enter the shell of a "female" to better ensure fertilization. It is said that a barnacle's penis is larger relative to its body size than that of any other animal.
The fertilized eggs develop into a larval form known as a nauplius. In this stage it may undergo several molts while living in the plankton for periods of up to half a year. Just before it is ready to settle down and raise a family of its own, the nauplius transforms into a cyprid larva. The cyprid does not feed. It's primary purpose is to sense potential sites to settle down on. It may assess various characteristics of the substrate such as texture, geology, chemistry and how damp it is.
Barnacles are actually considered delicacies in countries like Japan, Spain, Portugal and Chile. Way back in the 1970s I made a barnacle and limpet stew while on a survival hike to Little Harbor with my students. I survived it... just like I have the rest of my culinary attempts. I must have a cast iron stomach. Scientists are also interested in studying the very strong cement barnacles use to attach to rocks. They are hoping to synthesize it and market it commercially. I wish they had succeeded much earlier. If so, they might have discovered the secret to removing all the barnacles from the hull of my old boat!
© 2018 Dr. Bill Bushing. For the entire archived set of over 750 "Dive Dry" columns, visit my website Star Thrower Educational Multimedia (S.T.E.M.) Home Page
Image caption: Thatched acorn barnacles and gooseneck barnacles; barnacles on gray whale's head and nauplius larva (courtesy of Wikipedia).