Crypsis in Paraxanthus Barbiger (Decapoda: Brachyura): Mechanisms Against Visual Predators

Abstract

Marine organisms have evolved a suite of responses to minimize the exposure to predators. Visual crypsis is one such strategy to avoid predation. Paraxanthus barbiger (Poeppig, 1836) is a species that exhibits different color morphotypes over heterogeneous substrates as a means of protection against visual predators. Our main objectives were to quantify the occurrence of color morphotypes over a three-year period and to investigate, via an experimental approach, on the possible mechanisms involved that would provide crypsis to this species. Field surveys occurred over a three-year period at two nearby sites on the central Chilean coast. Initial observations indicated that small juvenile P. barbiger exhibited higher degrees of color polymorphism than larger (> 20 mm carapace width) conspecifics. Furthermore, survival rates of small (< 10 mm carapace width) P. barbiger exposed to predators increased on heterogeneous substrata under both natural and laboratory conditions. Laboratory experiments further demonstrated that newly settled P. barbiger actively select heterogeneous substrata. Hence, cryptic responses of this species might reduce predation-mediated mortality through color pattern disruption of individuals with respect to their environment.