Dosima

Abstract: November 2011 saw an unprecedented irruption of buoy barnacles Dosima fascicularis in coastal waters off the Western Cape, South Africa. Buoy barnacles not uncommonly strand in the region attached to feathers, plastic litter and other small objects, but the 2011 irruption saw exceptional numbers of unusually large colonies (average 23.5 individuals; SD 18.5), most of which relied on their own floats. The largest individuals (49 mm capitulum length) were larger than previous records for the species. Buoy barnacles were first observed at sea off the Cape Peninsula on 2 November 2011. During the following three weeks they washed ashore along at least 500 km of coast from Paternoster on the West Coast to De Hoop, east of Cape Agulhas. Mass strandings attained densities of up to 42 (SD 23) colonies per metre of beach (n = 10), with a wet mass of around 10 kg m−2. They were accompanied by large numbers of bluebottles Physalia physalis and other neustonic organisms. Of 100 buoy barnacle colonies examined, only t...

Abstract: The stalked barnacle Dosima fascicularis secretes foam-like cement, the amount of which usually exceeds that produced by other barnacles. When Dosima settles on small objects, this adhesive is additionally used as a float which gives buoyancy to the animal. The dual use of the cement by D. fascicularis requires mechanical properties different from those of other barnacle species. In the float, two regions with different morphological structure and mechanical properties can be distinguished. The outer compact zone with small gas-filled bubbles (cells) is harder than the interior one and forms a protective rind presumably against mechanical damage. The inner region with large, gas-filled cells is soft. This study demonstrates that D. fascicularis cement is soft and visco-elastic. We show that the values of the elastic modulus, hardness and tensile stress are considerably lower than in the rigid cement of other barnacles.

Abstract: Dosima fascicularis is the only barnacle which can drift autonomously at the water surface with a foam-like cement float. The cement secreted by the animal contains numerous gas-filled cells of different size. When several individuals share one float, their size and not their number is crucial for the production of both volume and mass of the float. The gas content within the cells of the foam gives positive static buoyancy to the whole float. The volume of the float, the gas volume and the positive static buoyancy are positively correlated. The density of the cement float without gas is greater than that of seawater. This study shows that the secreted cement consists of more than 90% water and the gas volume is on average 18.5%. Our experiments demonstrate that the intact foam-like cement float is sealed to the surrounding water.

Abstract: The presence of the buoy barnacle Dosima fascicularis is first documented for Spanish waters. More than the half of the specimens collected was attached to tar pellets from the Prestige oil spill.