Does variable coloration in juvenile marine crabs reduce risk of visual predation?

We discovered that newly settled marine rock crabs, Cancer irroratus, exhib it a variety of non-adult colors early in life. This color polymorphism pre dominates in populations of minute juvenile crabs living in polychromatic h abitats where it apparently renders them inconspicuous to visual predators such as fish. Experiments revealed lower frequencies of non-adult color mor phs in monochromatic three-dimensional habitats with predators and polychro matic habitats from which predators were excluded. These patterns result fr om selective predation on visually contrasting color morphs. Adult crabs ar e monochromatic, conspicuous, and not associated with shelters. Both polymo rphic newly settled and monochromatic large individuals occur in environmen ts dominated by small predatory fish where larger adult crabs are at low ri sk of predation. Behavioral and visual crypsis may only be important early in life when post-settlement mortality is high, and survival at that stage determines recruitment and ultimately population densities. The well-known examples of camouflage among insects usually apply to adults who, unlike th ese marine counterparts, are small relative to their predators and thus rem ain vulnerable throughout their lives. Many other large marine crustaceans are cryptic only early in life, suggesting that this early developmental co lor polymorphism might be an important difference between marine and terres trial arthropods.