Marine animal colour patterns and visual perception in coral reef fishes? (2026)

Abstract

Coral reefs are home to a variety of uniquely patterned and colourful organisms, whose striking colour signals and patterns are comprised of diverse and complex traits. These traits include the brightness (luminance or achromatic properties), hue and saturation (chromatic properties) as well as pattern geometry (the spatial arrangement of pattern elements). These colour signals drive numerous fundamental ecological processes and mediate interactions between animals, including inter- and intra-specific communication and predator avoidance through defensive strategies such as camouflage, mimicry, aposematism and deimatic displays. However, the salience of a signal is not solely influenced by colour pattern components, but also by the behaviour of the signaller, the background against which the signal is viewed, the distance between the signaller and observer, and the observer’s own visual system, including spectral sensitivities and visual acuity. Therefore, to fully understand the function of defensive colouration – particularly, how these visual signals are designed to communicate the presence of chemical defences – it is essential to investigate and incorporate the visual system of the intended receivers, and to consider how it affects conspicuousness and detectability of these visual signals. Despite this, many studies of defensive colouration in coral reef organisms are still signaller-centric, often quantifying colours and patterns without incorporating the perceptual and ecological context of relevant receivers such as potential predators. Therefore, the extent to which these signals reliably convey the presence of chemical defences, and how the effectiveness of these signals varies across viewing conditions and observe types, remains unclear. This thesis addresses this knowledge gap by investigating how defensive colour patterns are perceived by ecologically relevant receivers in coral reef environments. Specifically, it aims to: (i) evaluate how differences in visual systems may potentially influence signal perception; (ii) quantify the conspicuous and detectability of colour patterns under varying environmental and behavioural contexts; and (iii) assess the relationship between visual signal design and the presence of chemical defences. These aims provide an integrative framework for understanding how defensive colouration functions as a multimodal communication strategy in visually complex environments.