Fig. 3. Example model predictions of dynamic tuning in macroalgae subjected to unbroken waves showing how inertial effects can dominate applied force. In the case of the large surface-canopy kelp Nereocystis luetkeana (solid line and the ordinate on the left), peak tensile force (including forces due to the momentum the plant acquires as it moves) may occur when the waves arrive at a frequency equal to half the natural frequency of the seaweed, and these forces may greatly exceed the tensile force from drag alone. (The natural frequency is the frequency at which the plant would tend to oscillate if nudged slightly in still water.) Similarly, in an erect understory kelp, Eisenia arborea (dashed line and the ordinate on the right), total bending moments (i.e. moments including forces due to the momentum the plant acquires as it moves) may at times substantially exceed bending moments that would arise from drag alone. In this situation, the tuning is most apparent when the dominant frequency of the waves is the same as the natural frequency of the alga. Note that these model predictions assume a zero longshore current; if one is present, it may partially offset the exceptionally large tension ratios seen for N. luetkeana. In both curves, the magnitude of the orbital velocities produced by the waves is held constant across frequency. Denny et al. (1998) provide full details on this topic.