concept

Rugosity

A measure of a surface's three-dimensional complexity: the ratio of the true distance traced across every crevice, branch and hollow to the straight-line distance between the endpoints. A flat sand bottom has a rugosity near 1; a dense coral reef can reach 2 to 5. The number matters because structure creates habitat: every crevice, overhang and branching canopy is a micro-environment with its own light, flow and refuge. The rougher the surface, the more ecological niches it packs — which is why a reef can host an enormous number of species on a tiny patch of seafloor.