Structural integrity of Ellisolandia elongata reef: a mechanical approach to compare tensile strengths in natural and controlled environments

Geniculate coralline algae are oases of biodiversity, providing nursery areas and shelter for the species that live among their fronds. The key of their success in the intertidal is the ability to withstand hydrodynamic forces. Under culturing conditions most of the physical and ecological stressors such as intense hydrodynamic forces and grazing are extremely reduced, thus affecting species mechanical properties and their response to external threats. The aim of the present study is to investigate tensile mechanical properties of Ellisolandia elongata cluster of fronds from natural (sheltered and exposed reef) and culturing conditions (after one month of culturing). The tensile test showed that the first failure stress (σI) was not significantly different between the natural and culturing conditions indicating that the two reefs were characterized by the same distribution of pre-existing, inherent structural flaws. Interestingly the σmax (maximum stress before rupture) was significantly different between the two conditions, with the culturing condition being more resistant to average load compared to the natural conditions. The maximum stress before rupture (σmax) showed the influence of the environment in reducing strength and elasticity of the fronds.