Barnacle Adhesion: Reattachment of the Adult Barnacle Chthamalus Fragilis Darwin to Polystyrene Surfaces Followed by Centrifugational Shearing

Abstract

Adult specimens of Chthamalusfragilis Darwin were removed carefully from the leaves and stalks of marsh grass and placed with their bases on the bottoms of polystyrene dishes containing sea water in order to allow reattachment of the animals. During overnight culture, animals secreted small volumes of a sea water-insoluble material which reattached the animals to the surface of the polystyrene dishes. The secreted material made a contact angle with the polystyrene surface of ~ 15?, indicating that, before setting, the liquid precursor of the set material has considerable wetting properties. Dishes with reattached barnacles were mounted in a centrifuge to load the animals in shear and were subjected to increasing speeds of rotation until each of the reattached barnacles became detached. Reattached barnacles sustained relative centrifugal forces of up to 6,800 x g before detachment, which usually occurred at the barnacle basis/ cement interface. The strength of adhesion of individual barnacles reattached to polystyrene ranged from 0.0014-0.3589 Newtons. Using the area of attachment between cement and polystyrene dish, the strength of adhesion averaged 1.05 x 105 Nm-2, with a range of 0.14 x 105 to 2.79 x 105 Nm-2. These data are comparable to forces of adhesion reported for the temporary attachment of cyprid larvae and the normal attachment of adult barnacles to plastics and other materials measured by techniques which load the animals in tension. Our observations and measurements indicate that the material secreted by adult barnacles under in vitro culture conditions exhibits significant adhesive properties. It is unlikely that adult barnacles detached from marsh grass reattach to polystyrene by Stefan effects. It is well known that barnacles secrete, under water, adhesive materials which facilitate and maintain their attachment to a variety of natural and man-made substrates including the coverings of other marine organisms such as other barnacles, mussels, oysters, crabs, turtles, fishes, and whales, bare and painted metals and woods, concrete, plastics, and various other synthetic materials. Attachment is initiated during a short period of the barnacle life cycle, the cyprid larval stage, towards the end of which exploring cyprids settle on a suitable substrate and secrete an adhesive which firmly binds the larvae to the surface (Nott and Foster, 1969). An extensive literature relates light (Visscher and Luce, 1928; Pomerat and Reiner, 1942), fluid flow rates (Smith, 1946; Crisp, 1955; Crisp and Stubbings, 1957; Rittschof et al., 1984), surface texture (Pomerat and Weiss, 1946; Gregg, 1948; Wethey, 1986), and other environmental factors to cyprid settlement (Barnes, 1970). Attached larvae quickly metamorphose to young adult forms and begin the sedentary phase of their life cycle (Doochin, 1951; Bernard and Lane, 1962; Walley, 1969). The strength of attachment of both cyprid larvae and postmetamorphic adult barnacles to a variety of substrates has been measured by several investigators. By attaching cyprids to an electrobalance and loading them in tension, Yule and Crisp (1983) determined that the strength of temporary attachment of exploring cyprid larvae of Semibalanus balanoides (L.) to slate panels exhibited forces in the range of 1.47 x 105 to 3.81 x 105 Newtons per square meter (Nm-2). The strength of temporary adhesion of exploring cyprids of S. balanoides to slate, glass, and several plastics was reported by Yule and Walker (1984b, 1987) to be in the range of 0.6-3 x 105 Nm-2, with larvae attaching more avidly to surfaces with inherently higher surface energies such as slate and glass. It has been argued that these ranges of forces do not support the view that suction is the underlying mechanism holding barnacle larvae in place (Yule and Crisp, 1983). The strength of adhesion of adult sessile