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Integrative and Comparative Biology Advance Access published online on March 29, 2006
Integrative and Comparative Biology, doi:10.1093/icb/icj031
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© The Society for Integrative and Comparative Biology 2006. All rights reserved. For permissions, please email: journals.permissions@oxfordjournals.org.

Complex Life-Histories of Marine Benthic Invertebrates: A Symposium in Memory of Larry McEdward

Good eaters, poor swimmers: compromises in larval form

Richard R. Strathmann 1 * and Daniel Grünbaum 2
1 Friday Harbor Laboratories, University of Washington, 620 University Road, Friday Harbor, WA 98250, USA
2 School of Oceanography, Box 357940, University of Washington, Seattle, WA 98195-7940, USA

* To whom correspondence should be addressed.
Richard R. Strathmann, E-mail: rrstrath{at}u.washington.edu


  Abstract

Compromises between swimming and feeding affect larval form and behavior. Two hypotheses, with supporting examples, illustrate these feeding-swimming trade-offs. (1) Extension of ciliated bands into long loops increases maximum clearance rates in feeding but can decrease stability of swimming in shear flows. A hydromechanical model of swimming by ciliated bands on arms indicates that morphologies with high performance in swimming speed and weight-carrying ability in still water differ from morphologies conferring high stability to external disturbances such as shear flows. Instability includes movement across flow lines from upwelling to downwelling water in vertical shear. Thus a hypothesis for the high arm elevation angles of sea urchin larvae, which reduce speed in still water, is that they reduce a downward bias imposed by the vertical shear in turbulence. Observations of sea urchin larvae in vertical shear and comparisons among brittle star larvae are consistent with the performance trade-offs predicted by the model. (2) Structures and behaviors that reduce swimming speed can enhance filtering for feeding. In the opposed-band feeding mechanisms of veligers and many trochophores, cilia push water to swim but movement of cilia relative to the water occurs when cilia overtake and capture particles. Features that may increase clearance rates at the expense of speed and weight capacity include structures that increase drag or body weight and a ciliary band that beats in opposition to the feeding-swimming current. Larval feeding mechanisms inherited from distant ancestors result in different swimming-feeding trade-offs. The different trade-offs further diversify larval form and behavior.

From the symposium "Complex Life-Histories in Marine Benthic Invertebrates: A Symposium in Memory of Larry McEdward" presented at the annual meeting of the Society for Integrative and Comparative Biology, January 4-8, 2005, at San Diego, CA.
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