Lines of dehiscence as a biomechanical strategy for controlling damage during blade development in the bull kelp Nereocystis luetkeana

Although tearing is most often considered mechanical damage, it plays a central role in blade development in the bull kelp Nereocystis luetkeana. Although developmental tearing has been described in other macrophytes, the presence of a line of dehiscence that directs fracture apart from reproduction or abscission remains rare and poorly understood. This study shows that lines of dehiscence in Nereocystis promote clean, longitudinal blade splits by reducing tearing strength and facilitating crack propagation in flow. These effects are especially pronounced in juvenile blades, in which anisotropic tearing properties have not yet fully developed. By combining structural weakening with flow-driven crack extension, Nereocystis generates new blades through a mixed strategy of physiological patterning and passive fracture, revealing a previously underrecognized biomechanical strategy for controlling damage and adjusting morphology.