In the ocean, [bioluminescence] is the rule rather than the exception.

Widder’s line underscores how common light-making organisms are in marine ecosystems, especially in the deep sea. It pushes back against a surface-world intuition that glowing life is rare or exotic, reframing bioluminescence as a dominant ecological strategy—used for camouflage, communication, attracting prey, and evading predators. The phrasing “rule rather than the exception” also functions rhetorically: it invites readers to revise their baseline assumptions about the ocean as a largely dark environment and to recognize that much of marine life operates through sensory channels (light signals) that humans seldom witness directly.