The role of coloration and behaviour in the camouflage of the common cushion star, Asterina gibbosa

Many marine invertebrates exhibit high variation in body coloration that can serve different adaptive functions, including camouflage. In many animals, effective concealment is a three-way interaction between body appearance, behaviour, and the substrate. However, it is generally not well understood in many animals how camouflage is achieved in individuals when there exists high, but fixed, intraspecific variation in coloration. Here, we tested whether variation in coloration and background choice of common cushion stars, Asterina ­gibbosa, can provide them with effective background matching. We used digital photography to quantify objectively the coloration of starfish and substrates in their intertidal environment and the match between starfish and preferred and non-preferred substrates. We demonstrated that starfish generally match their preferred substrate type (usually undersides and sides of boulders) more closely than other potential substrates and have continuous variation in coloration among individuals. Furthermore, we tested experimentally whether starfish actively selected a background type that individuals matched better. Regardless of individual coloration, starfish preferred dark over light experimental gravel type but showed no preferences between green and orange gravel. Our results indicate that starfish coloration and behaviour are likely to function both in camouflage and in finding shelters, but further work is needed to establish the function, if any, of variation in colour types.