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First published online May 1, 2006
Journal of Experimental Biology 209, 1894-1903 (2006)
Published by The Company of Biologists 2006
doi: 10.1242/jeb.02225
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The hydrodynamic effects of shape and size change during reconfiguration of a flexible macroalga

Michael L. Boller* and Emily Carrington{dagger}

Department of Biological Sciences, University of Rhode Island, Kingston, RI 02881, USA


Figure 1
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  		Fig. 1. Recirculating flow tank with modifications for direct measurement of reconfiguration. The overall length of the tank was 2.4 m; the working section was 0.15 mx0.15 mx0.30 m (WxHxL). Algae (in the working section) were inverted to keep the force transducer dry. The 45° mirror allowed for the visualization of the frontal area of the alga as it reconfigured in flow.

 

Figure 2
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  		Fig. 2. Shape parameters measured directly during reconfiguration. The stipe angle was defined as the angle between the tank wall (A), the stipe/holdfast junction (B) and the center of the stipe/crown interface (C). The crown angle was defined by the upper edge of the crown (D), the center of the stipe/crown interface (C) and the lower edge of the crown (E).

 

Figure 3
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  		Fig. 3. Drag (FD) on all Chondrus from 0 to 2 m s–1 water velocity. Thin lines are individual algae measured at ~0.1 m s–1 intervals. The broken lines are the upper and lower predicted drag for the largest and smallest individuals (based on Arep) using the reconfiguration drag model (Eqn 6).

 

Figure 4
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  		Fig. 4. Stipe angle versus velocity for a subset of Chondrus representing the range of values observed. The rapid change in angle at low velocity (<0.2 m s–1) resulted in the crown contacting with the tank floor. Subsequent change in angle was due to the compression of the crown, allowing the stipe to become more parallel to the flow. Different symbols represent individual algae.

 

Figure 5
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  		Fig. 5. Change in crown angle with velocity for a subset of Chondrus representing the range of values observed. Variability in angle at low velocity was due to changes in the position of branches within the crown. Subsequent changes in angle were due to the compression of the crown. Different symbols represent individual algae.

 

Figure 6
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  		Fig. 6. Change in frontal area (AF) with water velocity for a subset of Chondrus representing the range of values observed. Initial increases in area at low water velocities (<0.2 m s–1) were due to an overall posture change of individuals. Subsequent decrease in area was due to crown compression. Different symbols represent individual algae.

 

Figure 7
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  		Fig. 7. Normalized area versus velocity for all Chondrus. The line is aU, the exponential decay function describing the normalized area from 0.2 to 2.0 m s–1 (Eqn 4). Model parameters (±95% confidence intervals) are: a{infty}=0.44±0.02, aR=0.75±0.03, ßa=0.70±0.08 m s–1; R2=0.98. Ucrit,a (2.47 m s–1) is noted by the arrow.

 

Figure 8
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  		Fig. 8. Drag coefficient (CD) versus water velocity for all Chondrus. The line is CU, the exponential decay function describing CD from 0.2 to 2.0 m s–1 (Eqn 5). Model parameters (±95% confidence intervals) are: C{infty}=0.75±0.03, CR=0.87±0.12, ßC=0.42±0.08 m s–1 and R2=0.59. Ucrit,C (1.56 m s–1) is noted by the arrow.

 

Figure 9
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  		Fig. 9. Drag coefficient versus crown angle for representative Chondrus at low to intermediate water velocities (0.2 to 1.0 m s–1). Reconfiguration was inversely related to crown angle such that maximal reconfiguration approaches 0°. The thin lines are linear regressions for each individual. The thick broken line was for a rigid cone of variable shape, where the cone's crown angle was equal to the angle of the peak of the cone (Hoerner, 1965Go). The angles above the x-axis represent cone of equal frontal area but spire angles of 30, 90 and 150°, respectively.

 

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© The Company of Biologists Ltd 2006