Monterey Bay Aquarium Research Institute
Marine Botany

Mechanics of Articulated Coralline Algae

       Structural mechanics are an important characteristic of any alga.  Articulated corallines are the hardest plants known due to their calcium carbonate walled intergenicula. However, they are able to retain a certain amount of elasticity and flexibility through their uncalcified genicula. For articulates, the study of mechanics provides further insight into the balance that must be maintained between rigidity and flexibility.

       In the mechanics lab at Hopkins Marine Biology Station, our class attempted to evaluate aspects of the mechanical properties of various algae, including the geniculates. What we found confirmed that the articulates were moderately elastic. Our alga specimen easily withstood being stretched an extra 10% of its length. When pulled to 15% of normal length, the specimen fractured at one of its intergenicula. This result was similar to what occurs outside the lab. Washed up articulates usually show breakage at their holdfasts or genicula. Articulates do not commonly fracture at their intergenicula.          

biomechanics stress/strain curve

       Above is a plot of stress versus strain measured in the lab. With respect to this analysis, strain is defined as the amount of change in decimal form. Stress refers to the amount of force divided by the area of the genicula where fracturing was observed. For this specific genicula the dimensions were approximately 4 cm by .25 cm, for an area of 1 cm2.

Stress = Force (in mega-newtons) / .01 meters2

Applied strain was cycled between 0 and approximately 0.11, the point at which fracturing occurred. These data suggest that articulates are able to handle a surprising amount of force, up to 80 mega-newtons per square meter. Further research regarding the mechanics of articulated corallines could produce very interesting results.

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© 2001 Ian Ehrenreich. All rights reserved.