The Brighter the Light, the Darker the Shadow: The Impact of Artificial Light at Night on Coastal Invertebrate Behaviour and Physiology

Abstract

The widespread expansion of Artificial Light at Night (ALAN) due to human activities is dramatically altering natural light cycles, yet its full ecological consequences remain poorly understood. While previous studies have explored ALAN’s effects on isolated ecological processes, this thesis provides a novel, multifaceted investigation into how ALAN interacts with celestial light cues, climatic conditions, behavioural rhythms, and trophic interactions in coastal invertebrate communities. By examining multiple levels of biological organisation—from individual behaviour and physiology to population-level effects—this research offers new insights into how ALAN disrupts key ecological functions in nocturnal coastal ecosystems.

A field study revealed that ALAN significantly reduces T. saltator abundance and disrupts its migration patterns, demonstrating for the first time that ALAN can override natural celestial navigation. The study also showed that the interaction between ALAN, lunar phase, and cloud cover plays a critical role in modulating these effects—an aspect previously unexplored. A controlled mesocosm experiment further provided the first evidence that ALAN suppresses nocturnal locomotor activity, shifts peak behavioural rhythms, and disrupts the expression of circadian genes, diminishing the organism’s responsiveness to natural lunar cycles. Additionally, a novel dietary and microbiome analysis revealed that ALAN alters T. saltator's dietary diversity and gut microbial composition, suggesting potential ALAN-driven changes in nutrient cycling and ecological interactions.

By bridging behavioural, physiological, and ecological perspectives, this thesis provides unprecedented insights into ALAN’s far-reaching consequences on a keystone coastal species. The findings highlight the complex, multi-scale effects of artificial lighting, challenging traditional assessments that overlook its interactions with natural light cues and climatic conditions. This work advances our understanding of ALAN’s ecological impacts and underscores the urgent need for conservation strategies that account for its disruptive influence on biodiversity and ecosystem processes.

Date of Award	2025
Original language	English
Sponsors	Envision DTP
Supervisor	Stuart Jenkins (Supervisor), Amy Ellison (Supervisor), Thomas W. Davies (Supervisor) & David C. Wilcockson (Supervisor)