Skeletal morphology and material properties of a fragmenting gorgonian coral

• Published in: Marine ecology. Progress series (Halstenbek) 2002-03, Vol.228, p.131-141
• Main Authors: Boller, M. L., Swain, T. D., Lasker, H. R.
• Format: Article
• Language: English
• Subjects: Animal and plant ecology; Animal, plant and microbial ecology; Animals; Anisotropy; Asexual reproduction; Autoecology; Bending; Biological and medical sciences; Coral reefs; Corals; Flow velocity; Fundamental and applied biological sciences. Psychology; Glomerulonephritis; Gorgonacea; Marine; Material properties; Plexaura kuna; Protozoa. Invertebrata; Sea water ecosystems; Skeleton; Stiffness; Synecology
• ISSN: 0171-8630; 1616-1599
• DOI: 10.3354/meps228131

Among species in which fragmentation is an important mode of asexual reproduction, mechanisms that facilitate fragmentation should be advantageous. The Caribbean gorgonianPlexaura kunareadily fragments on reefs of the San Blas Islands, Panama, to form aggregations of genetically identical colonies. To understand the mechanics of fragmentation and the role of structural properties, the force required to break branches was measured on live colonies in the field, and morphology, flexibility, and strength of the axial skeleton were measured in laboratory experiments. Young’s modulus, used as a measure of stiffness, was higher inP. kunathan in many other gorgonians and significantly varied among clones, ranging from 2.859 to 6.073 GN m–2. This level of variation indicates that drag should vary among clones due to differences in their flexibility. Of the morphological traits measured, coplanar constrictions influenced the force required to break a branch while anti-planar constrictions and branch anisotropy did not. The modulus of rupture, a measure of the strength of the branch, significantly varied among clones ofP. kuna, ranging from 50.87 to 92.58 MN m–2. Using hydrodynamic theory we predict that the 55% variation in skeletal strength is sufficient to produce variation in fragmentation rate among clones. The stiffness of the skeleton of some colonies may prevent bending and shedding of drag resulting in failure due to the weakness of the skeleton. Clonal variation in flexibility and strength provides a mechanism through which selection may act to favor fragmentation and clonal growth.