Buoy Barnacles arrive on our coastline

by Rob Tarr in January 2011 - Marine Scene

It was interesting to note the degree to which a lowly, and to all intents, uninteresting little critter managed to grab some media attention during November 2011. There were various, internet articles and radio interviews.

The reason for the interest was the extreme rarity of the event in Western Cape waters; hundreds of Bouy Barnacles washed up on our beaches from the west coast to Cape Agulhas, and probably even further, in what was described as a “massive bloom”. Regular, observant, beach walkers were phoning friends and emailing pictures trying to find out more about these creatures that no-one had apparently seen before. By all accounts this was an once-in-a-lifetime event – experienced marine biologists and marine life enthusiasts had never before seen Bouy Barnacles on South African shores.

Buoy Barnacles, Dosima fascicularis are broadly related to insects, crustaceans and spiders, being joint-legged animals, and they feed on small planktonic organisms that they capture by repeatedly extending their star-shaped array of maxillae (legs) into the water. Interestingly, unlike other barnacles whose legs have fine filter-feeding webs attached, the legs of the Buoy Barnacle seem more adapted for grasping particles than to filtering them out of the water. But the thing that sets them apart from their other barnacle cousins is that they are uniquely able to float on the surface of the ocean using their own self-created ‘buoy’ or flotation device. The tiny larvae will first opportunistically settle on any small particle found floating on the surface, and then, as the animal grows, it produces its own float: a foam-like substance that looks, feels and acts like a piece of polystyrene. Often, others attach to the same float, and they then communally grow the float so that it supports the group.

Why did this big wash-up of Buoy Barnacles occur? No-one can say for sure, but this species is reported to occur in a region of the South Atlantic Ocean called the subtropical convergence zone. It is here where the cold waters of the Antarctic region meets the warmer waters from the north, approximately 40 degrees south. (They also occur in other oceans of the world). It is possible that the South Atlantic current that passes west of Cape Town brought floating organisms (called pleuston by scientists who categorize everything!) west of Cape Town and that subsequent extensive south-westerly winds then blew the organisms onto our beaches.

The great scientist Charles Darwin also studied the Buoy Barnacle, and described the float in 1851. He became fascinated by barnacles in his later years and spent eight years studying them, finding answers to numerous of his questions on animal adaptations in the process. However it was apparently an arduous journey, as he is quoted as saying: “I hate a barnacle as no man ever did before.”