Surface properties of the skin of dolphins

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Baum, C. , Simon, F. , Meyer, W. , Fleischer, L. G. , Siebers, D. , Kacza, J. and Seeger, J. (2002): Surface properties of the skin of dolphins , 11 th Int. Con. Mar. Cor. Biofoul., San Diego .
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Summary. In delphinids small biofoulers are potentially challenged to high shear water flow and liquid-vapor interfaces of air bubbles during jumping. In the present study we investigated the skin of the pilot whale, Globicephala melas, with emphasis on topological, biochemical and rheological properties of the skin surface enhancing the efficiency of self-cleaning based on the common behaviour of dolphins.The surface properties were characterized combining rheological measurements with cryo-scanning electron microscopy (C-SEM), transmission electron microscopy (TEM), photoelectron spectroscopy (XPS), and enzyme histochemistry.The results obtained show that the skin of the pilot whale exhibited only marginal loads of biofoulers. The skin surface was even and smoothed by a hydrated jelly material alternating with embedded lipidic droplets. The surface topology demonstrated displayed no particular microniches in the size of biofoulers. The jelly material derived from deeper intercellular space between stratum corneum lamellae and was enriched by various hydrolytic enzymes. Unlike the mucoid-based properties of marine fouling polymers, the rheological mesurements revealed the high elasticity in combination with high energy dissipation rates of the jelly material of the dolphin skin assembled from covalently cross-linked aggregates. XPS measurements carried out on deep-frozen skin samples and the bare jelly material showed the presence of free amino groups and lipidic ester groups, which were dominant chemical features of the skin surface.Since cetaceans lack skin glands the protective power of the skin was considered to be based on the biochemical adaptation of the corneocytes. In regard to the higher shear resistance of the jelly material collected from the stratum corneum contrasting to the biophysical properties of mucoid-based biopolymers, we concluded that the gel is not a substitute of mucus, can withstand higher shear regimes and evens the skin surface. The retention of hydrolytic enzymes incorporated within the gel to some extent broadens the self-cleaning abilities of the dolphin integument by degrading non-dolphin biopolymers. Moreover, the hydrolytic enzymes initiate the desquamation process and probably remove contaminations as large as the desquamating cells (50x80 µm). Since the skin surface exhibits less contact area and microniches biofoulers may adhere to or hide within, we argue that biofoulers challenged to air bubbles or high shear water flow during jumping are easily removed from the skin surface. In this connection, the implications to the self-cleaning abilities are discussed, as based on chemical heterogeneity of the amphiphilic skin surface of the pilot whale and the fouling polymers of conditioning films in relation to the hydrophobic liquid-vapor interfaces of air-bubbles and hydrophilic water flow.We thank Dr. D. Bloch and Dr. H.-P. Joensen, University of the Faroe Islands, for their help in specimen collection from legal harvest. This study was supported by a grant of the Deutsche Forschungsgemeinschaft (ME 1755/1-1 and 1-2).

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