. The Biological bulletin. Biology; Zoology; Biology; Marine Biology. SEA FAN ORIENTATION 133 cm~2, and cannot withstand great deformations. This accounts for the shape taken by fans as they are bent by waves: the basal portion bends very little but the lower modulus, highly deformable upper part is bent to a position parallel to the direction of wave motion. Thus the parts of the fan farthest from the reef surface meet the maximum current velocities (see Discussion, part I) and are the very parts that offer least elastic resistance to the current. Since the current velocity is greater farther
. The Biological bulletin. Biology; Zoology; Biology; Marine Biology. SEA FAN ORIENTATION 133 cm~2, and cannot withstand great deformations. This accounts for the shape taken by fans as they are bent by waves: the basal portion bends very little but the lower modulus, highly deformable upper part is bent to a position parallel to the direction of wave motion. Thus the parts of the fan farthest from the reef surface meet the maximum current velocities (see Discussion, part I) and are the very parts that offer least elastic resistance to the current. Since the current velocity is greater farther from the reef surface, the effect of this orienting force is greater on the. larger B D FIGURE 3. Diagram of the orientation of a sea fan (or of any flat, flexible object attached by a stem continuous with a midrib) to the direction of an impinging current as seen from above. Dashed arrows and line: direction of flow. Dotted line: orientation of the fan blade in the absence of current. Outlined arrows: relative magnitude of the forces exerted against the current by leading and trailing edges of the fan blade. A: fan blade parallel (0°) to current and showing no twist. B: fan blade at low angle to the current and showing maximum twist being applied to the stem. C: fan blade at larger angle to the current and showing low twist. D: fan blade perpendicular to the current, also showing no twist. DISCUSSION It is highly probable that water movements are the dominant cause of the oriented growth of sea fans. Theodor and Denizot (1965) state that mechanical stability of flexible planar organisms such as sea fans is realized only when the plane of the fan is perpendicular to the direction of impinging water movements. They also state that any twisting of the bases of sessile foliaceous organisms that result from nonperpendicular orientation would decrease their resistance to frac- ture. By way of partial explanation of why either of these statements should be true, we present t
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Keywords: ., bookauthorlilliefrankrat, booksubjectbiology, booksubjectzoology
