Holding (not so) fast: surface chemistry constrains kelp bioadhesion

Benthic macroalgae must attach firmly to the substrate to prevent being detached and washed away by water motion. The success of the bioadhesion system can be strongly influenced by surface chemistry and so this should be optimized for large-scale cultivation. This is especially important during the early stage of cultivation when the juveniles have little thigmotactic attachment, which is needed to interlock with surface rugosity. Juvenile sporophytes of Saccharina latissima (Phaeophyceae) were directly applied onto polymer films of varied surface composition to determine how the attachment force of the developing holdfast was influenced by surface chemistry. Eight polymer chemistries were examined: polyamide (PA), polyethylene (PE), polyester (PES), polypropylene (PP), polymethylacrylate (PMA), polyvinylalcohol (PVA), polyvinylchloride (PVC) and thermoplastic polyurethane (TPU). The PP and PE were also examined as three grades: commercial grade with additives, pure polymer, or pure polymer following a corona treatment. Additive inclusion and corona significantly reduced the water contact angle (p < 0.0001), indicating an increase in the surface free energy available for bioadhesion. After 6 weeks, the attachment force was greatest on PVA, PA and PVC (0.19-0.33 N), correlating strongly with the achieved biomass (R-2 = 0.68). Additives and corona treatment improved holdfast attachment force, particularly corona treated PE (0.28 +/- 0.08 N: 0 N without corona). Generally, attachment force appeared greatest on chemistries with a contact angle of 60-75 degrees. These results confirm that the bioadhesion of the phaeophyte holdfast is strongly influenced by the surface free energy of the substrate chosen. Through alteration of the additive composition, attachment could be improved to create bespoke cultivation substrates. Corona treatment is highlighted as a very suitable method for improving holdfast attachment force during cultivation.