Implications of hyposaline stress for seaweed morphology and biomechanics

Seaweeds are primary producers that form a key component of coastal ecosystems. In estuaries and the intertidal zone they are frequently exposed to temporary hyposaline conditions. Previous research has shown that seaweed health status and photosynthetic activity are reduced due to hyposaline stress, but its effects on seaweed physical properties are unknown. This knowledge gap has important implications for the prediction of seaweed hydrodynamics and mechanical failure due to hydrodynamic stress, particularly in extreme conditions (e.g. storm events). In this study, we begin to address this knowledge gap by investigating the effects of hyposaline stress on the morphological and mechanical properties of the kelp Saccharina latissima (order Laminariales). We analysed the morphology of 23 seaweed blades and performed tension and bending tests on more than 90 samples prepared from them. The obtained data provide evidence that both morphology and mechanics of S. latissima are affected by hyposaline stress, i.e.: (i) blades bleach, develop blisters underneath the cortex, and change dimensions (increased volume and thickness, decreased width); and (ii) blade material becomes more flexible and more difficult to break (i.e. tougher). The results indicated a significant correlation between the time of exposure and changes in biomechanics of S. latissima with potential implications for seaweed hydrodynamics and survival strategies.