{"word_count": 503, "character_count": 3257}
Résumé de la communication de Mimi A. R. KOEHL (University of Berkley, California, USA) donnée à l’occasion du séminaire Les constructions en milieu marin / Constructions in marine environment du 14 au 19 mars 2016At the meeting about Marine Constructions, I focused on sessile marine organisms attached to the sea floor and exposed to moving water. These organisms depend on moving water for transport of nutrients, oxygen, wastes, gametes, and propagules. However, they also risk being dislodged or broken by moving water. Therefore, their body designs represent trade-offs between minimizing and maximizing the effects of ambient water flow. I used the giant kelp, Nereocystis leutkeana, to illustrate how body design affects the performance of an organisms in moving water, and also how moving water can alter body design.Many species of macroalgae have flat, strap-like blades in habitats exposed to rapidly flowing water, but have wide, ruffled blades at protected sites. We used the giant bull kelp, Nereocystis luetkeana, to investigate how these ecomorphological differences affect performance and how they are produced. The undulate blades of N. luetkeana from sites with low flow remain spread out and flutter erratically in moving water, thereby enhancing interception of light, but also increasing drag. In contrast, strap-like blades of kelp from habitats with rapid flow collapse into streamlined bundles and flutter at low amplitude in flowing water, thus reducing both drag and interception of light. Transplant experiments in the field revealed that shape of the blade in N. luetkeana is a plastic trait. Laboratory experiments in which growing blades from different sites were subjected to tensile forces that mimicked the hydrodynamic drag experienced by blades in different flow regimes showed that change in shape is induced by mechanical stress. During growth experiments in the field and laboratory, we mapped the spatial distribution of growth in both undulate and straplike blades to determine how these different morphologies were produced. The highest growth rates occur near the proximal ends of N. luetkeana blades of both morphologies, but the rates of transverse growth of narrow, strap-like blades are lower than those of wide, undulate blades. If rates of longitudinal growth at the edges of a blade exceed the rate of longitudinal growth along the midline of the blade, ruffles along the edges of the blade are produced by elastic buckling if a blade is wide enough. In contrast, flat blades are produced when rates of longitudinal growth are similar across the width of a blade. Because ruffles are the result of elastic buckling, a compliant undulate N. luetkeana blade can easily be pushed into different configurations (e.g. the wavelengths of the ruffles along the edges of the blade can change, and the whole blade can twist into lefthanded and right-handed helicoidal shapes) which may enhance movements of the blade in flowing water that reduce self-shading and increase mass exchange along blade surfaces. Principles learned from design of organisms can inform the design of man-made structures in marine environments. However, organisms can grow, remodel, and heal, while man-made structures cannot (yet).Summary