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.
Highlights
Sessile marine organisms secrete adhesives which are cured underwater and which remain durable in the water [1,2]
After metamorphosis from the cyprid to the juvenile, both acorn and stalked barnacles usually produce only a thin layer of permanent adhesive, the so-called cement, by which they adhere to the substratum
We could show that the elastic modulus and hardness of the cement surface were higher in seawater than in distilled water
Summary
Sessile marine organisms secrete adhesives which are cured underwater and which remain durable in the water [1,2]. Barnacles are among the most troublesome and dominant fouling organisms [4]. They settle as cypris larvae on any hard substratum, whether it is man-made such as ships and bridges or organisms such as crabs and turtles. After metamorphosis from the cyprid to the juvenile, both acorn and stalked barnacles usually produce only a thin layer of permanent adhesive, the so-called cement, by which they adhere to the substratum. The cells enclosed in the cement contain gas [5 –7], the nature of which remains unknown. The excretion of CO2 together with the cement is doubly advantageous for the animal: it causes the formation of gas-filled cells in the cement and contributes to the pH regulation in the haemolymph [8]
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