This project explored the niche separation, protective coloration, and chemical defences of the polymorphic nudibranch Polycera quadrilineata through a series of work packages (WPs). Field observations (WP1) revealed no evidence of niche separation between colour morphs, as both morphs were equally distributed across microhabitats. Image analysis demonstrated that both morphs provide camouflage against their natural backgrounds in terms of coloration, with the dark morph showing more effective camouflage in terms of luminance. The dark morph may use distance dependant aposematism, with the black stripes blurring from a distance, but contrasting with yellow and white stripes when viewed in close proximity. Behavioural experiments indicated that fish predators more readily attack the light morph, but both morphs were equally rejected and avoided after initial attacks. Overall, results support different modes of protective coloration, with the light morph more conspicuous against natural backgrounds from a distance, and the dark morph with more contrasting internal patterns when viewed up close.
In WP2, the study examined predation risk and habitat preference, finding no significant differences in microhabitat associations or predator-driven selection between morphs. The light morph was more frequently attacked but survived similarly to the dark morph. Nudibranchs did not display preferences for specific bryozoan-algae combinations, although the light morph showed less inclination to visit seaweed without bryozoans.
WP2 focused on chemical profiling and the “go slow” hypothesis. Conspicuousness and chemical defences were assessed, with the light morph being more visually conspicuous from a distance against natural backgrounds and the dark morph being more conspicuous up close due to high contrast of the internal colour pattern. Both morphs were equally chemically defended to the fish predator Lipophyrs pholis. Ongoing work, delayed due to the COVID-19 pandemic, involves chemical analysis of nudibranch tissue in collaboration with Italian researchers. Due to the COVID-19 delay, additional studies on nudibranch chemical defences and predation strategies were conducted, supporting the “go slow” hypothesis.
