Colour change in a filefish (Monacanthus chinensis) faced with the challenge of changing backgrounds

Abstract

The marine macroalga Caulerpa taxifolia is increasing its distribution worldwide, both within its natural range, where it can replace seagrass following a disturbance, and in areas where it is invasive. C. taxifolia presents a bright green background colouration for inhabitants, while seagrass habitats are typically much deeper green in coloration. The fan-bellied leatherjacket, Monacanthus chinensis inhabits both seagrass Zostera muelleri and C. taxifolia habitats in Moreton Bay, Australia and is camouflaged in these contrasting habitats by brown and bright green colour morphs, respectively. Aquarium experiments measuring colour change of brown and green morphs with respect to contrasting habitats (i.e., brown morphs in C. taxofolia and green morphs in seagrass) revealed that over 21 days, brown morphs significantly altered their skin colouration towards the colouration of green morphs, but green morphs did not alter their colouration. In a habitat preference experiment, brown morphs, which match the colouration of the seagrass, significantly preferred seagrass to C. taxifolia, whilst green morphs showed no preference. We conclude that variations in C. taxifolia coverage present a substantial challenge to this species at short time scales (weeks). This challenge may be overcome by colouration changes at longer timescales assuming fish can survive predation during the adjustment period.