The Impact of Changing Artificial Light Spectra on Marine Visual Ecology

ORCID

Abstract

Artificial light at night (ALAN) is transforming natural lightscapes worldwide, creating unprecedented nocturnal conditions to which few species are adapted. As a pervasive form of sensory pollution, it alters both when organisms are active and how they perceive one another and their environments. Yet despite a decade of rapid expansion in ALAN research, its influence on visually guided processes such as camouflage – among the most fundamental and evolutionarily significant of anti-predator adaptations – remains strikingly underexplored.This thesis applies a visual ecology perspective to examine how ALAN disrupts camouflage and the ecological and evolutionary processes it supports. Using the intertidal gastropod Littorina obtusata and its fucoid algal habitat as a model, I combine behavioural experiments, field studies, and hyperspectral reflectance analyses to test the hypothesis that ALAN modifies the selective landscape for colour-based traits through both direct (perceptual and behavioural) and indirect (habitat-altering) means. Chapter 1 synthesises evidence from visual ecology, camouflage, and light-pollution research, establishing a conceptual framework for understanding camouflage as a dynamic interaction between signal, background, and observer. It identifies multiple mechanisms by which artificial lighting could alter camouflage effectiveness, including spectral shifts, changes to colour perception, and disruption of the circadian rhythms that often dictate visual encounters.In Chapter 2, a laboratory predation experiment shows that broad-spectrum (‘white’ LED) ALAN alters predator-prey dynamics, reversing the pattern of colour-based selection by green shore crabs (Carcinus maenas) of L. obtusata morphs observed under control conditions, inverting the relative vulnerability of yellow- and brown-shelled individuals, and reducing overall predation. These effects disappear under spectrally filtered (‘mitigation’) light, confirming the crucial role of broad spectrum lighting technologies in expanding ALAN’s ecological impact. Chapter 3 extends the investigation to the habitat level, revealing that ALAN alters the reproductive phenology of key fucoid algae species (Ascophyllum nodosum, Fucus serratus) in the field, shifting the seasonal timing and colouration of the very backgrounds against which intertidal prey such as Littorina conceal themselves. Chapter 4 integrates six-month, multi-site field observations with hyperspectral reflectance analyses to show that both the frequency of L. obtusata colour morphs and within-morph brightness vary systematically along an ALAN gradient, suggesting that artificial lighting may indeed alter selective pressure on colour morphs in wild populations.Together, these findings demonstrate that ALAN has the potential to disrupt camouflage via interacting perceptual and ecological pathways, changing how predators behave, how prey are seen, and the appearance of the environments that mediate their encounters. The consequences extend beyond immediate behavioural effects, implying potential shifts in predator-prey balance, population composition, and the maintenance of colour polymorphism. In Chapter 5, I argue that these results position light pollution as a novel evolutionary force associated with changing visual selection in coastal ecosystems. Methodologically, the thesis highlights the value of integrating behavioural ecology with hyperspectral reflectance spectrometry to quantify colour variation and camouflage effectiveness under changing light regimes. Conceptually, it positions light pollution within a visual ecology framework, showing that its impacts are best understood through the perceptual mechanisms it alters rather than through light intensity alone. Collectively, the results underscore that the impacts of even apparently subtle shifts in illumination have the potential to ripple through perceptual, behavioural, and ecological levels of organisation, altering how species interact within increasingly illuminated coastal ecosystems.

Awarding Institution(s)

University of Plymouth

Supervisor

Thomas Davies, Louise B. Firth, Tim Smyth

Keywords

Marine Biology, marine biology, Marine ecology, sensory ecology, Ecology, crustacean, Gastropod, Macroalgae, Seaweed, snails, light, Pollution

Document Type

Thesis

Publication Date

2026

Embargo Period

2026-12-03

Deposit Date

June 2026

Creative Commons License

Creative Commons Attribution-NonCommercial 4.0 International License
This work is licensed under a Creative Commons Attribution-NonCommercial 4.0 International License

This document is currently not available here.

This item is under embargo until 03 December 2026

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