Texture analysis of Laminaria digitata (Phaeophyceae) thallus reveals trade-off between tissue tensile strength and toughness along lamina

Texture analysis is a method to test the physical properties of a material by tension and compression. The growing interest in commercialisation of seaweeds for human food has stimulated research into the physical properties of seaweed tissue. These are important parameters for the survival of sessile organisms consistently exposed to turbulent flow and varying drag-forces. These tactile properties also affect consumer perception and acceptance of materials. Here, we present a standardised method to determine these physical properties using, as an example, the brown seaweed Laminaria digitata (Hudson) J.V. Lamouroux, which is prevalent on coastlines along the northern Atlantic Ocean. Morphological features of a healthy L. digitata thallus (lamina) seem modified to withstand physical distress from hydrodynamic forces in its wave-swept habitat. The trade-off in tissue responses to tensile and compression forces along the lamina, linked to an age gradient, indicates a twinned alignment of its cellular microstructure, similar to those of modern nanotechnology, to optimise the toughness and flexibility of constituent tissue. Tensile strength increased from young to old tissue along a positive toughness gradient of 75%. Based on our results, a short interpretation is given of the heterogeneity in L. digitata lamina from morphological, ecological and physiological perspectives