RT Journal Article
SR Electronic
T1 Intertidal sea stars (<em>Pisaster ochraceus</em>) alter body shape in response to wave action
JF The Journal of Experimental Biology
JO J. Exp. Biol.
FD The Company of Biologists Ltd
SP 1717
OP 1725
DO 10.1242/jeb.078964
VO 216
IS 9
A1 Hayne, Kurtis J. R.
A1 Palmer, A. Richard
YR 2013
UL http://jeb.biologists.org/content/216/9/1717.abstract
AB Sea stars are some of the largest mobile animals able to live in the harsh flow environment of wave-exposed, rocky intertidal shores. In addition, some species, such as the northeastern Pacific Pisaster ochraceus, are ecologically significant predators in a broad range of environments, from sheltered lagoons to the most wave-exposed shorelines. How they function and survive under such an extreme range of wave exposures remains a puzzle. Here we examine the ability of P. ochraceus to alter body form in response to variation in flow conditions. We found that sea stars in wave-exposed sites had narrower arms and were lighter per unit arm length than those from sheltered sites. Body form was tightly correlated with maximum velocity of breaking waves across four sites and also varied over time. In addition, field transplant experiments showed that these differences in shape were due primarily to phenotypic plasticity. Sea stars transplanted from a sheltered site to a more wave-exposed site became lighter per unit arm length, and developed narrower arms, after 3 months. The tight correlation between water flow and morphology suggests that wave force must be a significant selective factor acting on body shape. On exposed shores, narrower arms probably reduce both lift and drag in breaking waves. On protected shores, fatter arms may provide more thermal inertia to resist overheating, or more body volume for gametes. Such plastic changes in body shape represent a unique method by which sea stars adapt to spatial, seasonal and possibly short-term variation in flow conditions. Ahlateral projected area of one half of the sea star (mm2)ALaverage arm length (mm)AMLPmaximum lateral projected area (mm2)ANCOVAanalysis of covarianceAplanarplanar area (mm2)CDcoefficient of dragCLcoefficient of liftDSDixon Island, shelteredFDforce of drag (N)FLforce of lift (N)hCheight of the sea star in the centre of the body (mm)HEHelby Island, exposedhTheight at the tip of the sea stars arm (mm)Nsample sizeSESeppings Island, exposedSSSeppings Island, shelteredVwater velocity (m s−1)ρdensity of seawater (kg m−3)