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In this work we examine how particle dynamics and orientation patterns can revel information about fluid structures, how particles can be used as a device to measure fluid statistics, and how in return, fluid structures interact and influence the dynamics of particles. We begin by studying the spatial field of orientations of slender fibers that are advected by a two-dimensional (2D) fluid flow. We introduce emergent scar lines as the dominant coherent structures in the orientation field of passive directors in chaotic flows. We use the standard map as a simple time-periodic two-dimensional flow that produces Lagrangian chaos. This class of flows produces persistent patterns in passive scalar advection, and we find that a different kind of persistent pattern develops in the passive director orientation field. We identify the mechanism by which emergent scar lines grow to dominate these patterns at long times in complex flows …