Hydromechanical Adaptations in AlcyoniumSidereum (Octocorallia)

  • Mark R. Patterson


The relation between colony size and shape vs. flow regime was investigated in a boreal species of octocoral, Alcyonium sidereum with particular regard to two hydrodynamic problems faced by these organisms: (1) maximizing the area of feeding surfaces presented to flow while (2) limiting potentially damaging drag forces induced by water movement.

The results are summarized as follows: (1) A. sidereum exhibits three general morphologies depending upon flow regime: A) a stubby lobed morphology (CD = 0.37) is found in areas characterized by turbulent flow of high velocity (U > 25 cm/s), B) an ellipsoidal plate morphology (CD = 0.76) is found in areas of predictable bi-directional flow (10 < U < 25 cm/s), and C) an elongate pencil-like morphology (CD = 0.60), occasionally arborescent, is characteristic of calm areas (U < 10 cm/s). (2) Contraction of A. sidereum colonies during hydromechanical stress reduces their height above the substrate as well as their greatest horizontal dimension by 40–80%, significantly reducing drag. The normalized reduction is significantly greater in the height above the substrate indicating the importance of seeking the wall boundary layer during periods of strong flow. (3) Peak drag forces experienced by finger-like, lobed, and ellipsoidal colonies (isovolumetric) during storms were estimated to be 17 N, 9 N, and 23 N respectively. (4) Colony size (height above substrate) exhibits a positive correlation with water movement.


Wind Tunnel Flow Regime Drag Force Colony Size Drag Reduction 
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Copyright information

© Springer Science+Business Media New York 1980

Authors and Affiliations

  • Mark R. Patterson
    • 1
  1. 1.Museum of Comparative Zoology Laboratories 105Harvard UniversityCambridgeUSA

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