The importance of wave exposure on the structural integrity of rhodoliths

The structure (both gross morphology and internal cellular) of rhodoliths (free-living forms of coralline algae) are important factors in the ability of rhodoliths to create complex habitats. Using Finite Element Analysis, models of the internal structure of rhodoliths have been interrogated to assess how changes to the cellular structure affect structural integrity. These models are accurate in their portrayal of the internal skeleton, yet they fail in other ways. Specifically, they lack accurate environmental loads and material properties (Young's modulus), which form the basis of an accurate quantification of the structural integrity of rhodoliths. Here we measure the material properties of rhodoliths and quantify the hydrodynamic forces acting on them. Applying correct material properties and hydrodynamic forces, our results show that rhodoliths experience larger stresses than previously modelled. Water velocities representing storm surges cause internal stresses exceeding experimentally derived breakage stresses. As the intensity and frequency of storm surges are predicted to increase, the forces generated by them will result in breakage and hence affect their role as habitat builders.