Potential and limitations of finite element modelling in assessing structural integrity of coralline algae under future global change

Abstract

Abstract. Coralline algae are important habitat formers found on all rocky shores. While the impact of future ocean acidification on the physiological performance of the species has been well studied, little research has focused on potential changes in structural integrity in response to climate change. A previous study using 2-D Finite Element Analysis (FEA) suggested increased vulnerability to fracture (by wave action or boring) in algae grown under high CO 2 conditions. To assess how realistically 2-D simplified models represent structural performance, a series of increasingly biologically accurate 3-D FE models that represent different aspects of coralline algal growth were developed. Simplified geometric 3-D models of the genus Lithothamnion were compared to models created from computed tomography (CT) scan data of the same genus. The biologically accurate model and the simplified geometric model representing individual cells had similar average stresses and stress distributions, emphasising the importance of the cell walls in dissipating the stress throughout the structure. In contrast models without the accurate representation of the cell geometry resulted in larger stress and strain results. Our more complex 3-D model reiterated the potential of climate change to diminish the structural integrity of the organism. This suggests that under future environmental conditions the weakening of the coralline algal skeleton along with increased external pressures (wave and bioerosion) may negatively influence the ability for coralline algae to maintain a habitat able to sustain high levels of biodiversity.

Structural and Elemental Analysis of the Freshwater, Low-Mg Calcite Coralline Alga Pneophyllum cetinaensis

“…The structural integrity of Pneophyllum cetinaensis showed a highly heterogeneous distribution of elastic modulus and hardness within and between the specimens. Surprisingly, Hardness (H) and Elastic modulus (Er) in Pneophyllum cetinaensis are within the same range of value measured in different coralline algae species living in different marine environments (intertidal: [ 45 ], subtidal: [ 46 ]). Cristallographic size and texture play an important role in the optimization of the calcite material properties [ 47 ].…”

Impact of high CO2 on the geochemistry of the coralline algae Lithothamnion glaciale

“…Even in the long term experiment, we cannot predict if these changes in the elemental composition will be permanent and if so, the extent of how these changes in the elemental composition will affect the coralline algae. The loss in elasticity and hardness (embrittlement) together with the highly heterogeneous structure will potentially increase the susceptibility of the thallus to fracturing in an increasingly wave dominated environment 21 . Increased likelihood of fracturing or damage to the algae will have detrimental impacts to the future ability of coralline algae to perform its ecosystem function.…”

“…In sea urchins the high Mg-Calcite phase has higher mean elastic modulus (E) and hardness (H) values compared to pure calcite 20 . Finite Element Modelling of the growth structure of coralline algae specimens cultured under high CO 2 indicates a reduction of the algae’s ability to withstand predation and erosion due to wave action in response to the changes in growth geometry of the organisms 15 21 . However, the added effect of changes in elemental concentration and mineral growth have not been quantified to date and might indicate synergistic or antagonistic impacts of ocean acidification on the structural performance of coralline algae.…”

pH up-regulation as a potential mechanism for the cold-water coral <i>Lophelia pertusa</i> to sustain growth in aragonite undersaturated conditions

“…While some species have been shown to continue to grow even under low pH conditions, a weakening of the ultra-structure can impair ecosystem functionality, i.e. its ability to withstand predators and wave action (Chan et al, 2012;Ragazzola et al, 2012;Melbourne et al, 2015).…”