Universiteit Leiden

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Dani Crowley

PhD candidate

D. Crowley MSc
+31 71 527 4759

My interests lie in ecology, anthropogenic habitat disturbance and population dynamics within the aquatic environment. The focus of my PhD, will be the effects of light pollution on freshwater fish behaviour and physiology, more specifically during migration and development.

More information about Dani Crowley


My PhD project forms part of the BioClock consortium; a large scale investigation into the effects of light pollution on the biological clock. My role within the consortium is to investigate the impact of light pollution on daily and seasonal rhythms of migratory freshwater fish.

Light in the aquatic environment directly influences the visual conditions experienced by fish. The duration and intensity of light during daily and seasonal rhythms affect an array of physiological and behavioural processes within fish; such as orientation, foraging, breeding and migration. When artificial light is introduced into the aquatic environment, the difference between day and night becomes less clear. This is especially concerning for diurnal and nocturnal migratory fish, as the natural cues used for the triggering of and navigation during migration may no longer be distinguishable from artificial light, which can in turn influence energy expenditure and migration success.

To investigate this, I will conduct various indoor and outdoor studies.

By, cross-correlating telemetry data sets of tagged silver eels with light pollution-, meteorological- and astronomical data from across the Netherlands, we will estimate the contribution of light pollution to the dramatic decline in eel population.

Using swimming respirometers in the field, and the Migradrome-tilted flume in the lab, we will test migrating and non-migrating sticklebacks from, both light and non-light polluted areas to understand if these differing migratory types vary fundamentally in swimming physiology and possibly clock rhythmicity, which could be used as indicators for how they will cope in a light polluted environment.

In addition to this, using a mesocosm system with natural conditions, we will run caged experiments with PIT tagged sticklebacks. These cages will be experimentally manipulated with varying light conditions and activity over time will be monitored.

During my PhD I am supervised by assistant professor dr. Christian Tudorache, associate professor dr. Hans Slabbekoorn and professor dr. Joke Meijer. For this PhD I will be working within the interdisciplinary (humans, plants and animals) BioClock consortium, along side various individuals from across the Netherlands.

Brief biography

In 2020, I acquired a MSc in Marine Biology from the University of Groningen. It was here that I had the opportunity to research light in the aquatic environment, an interest I had previously acquired after seeing the impact of light pollution on sea turtles in Greece. During my studies, I investigated the consequences of costal light pollution on marine organisms across multiple trophic levels. Following this, my thesis focused on researching light driven habitat choice in Lake Victoria cichlids. 

After completing my MSc, I worked in a research aquarium as an animal care taker.

In January 2022, I started my PhD on the effects of light pollution on freshwater fish behaviour and physiology - migration and development.

PhD candidate

  • Science
  • Instituut Biologie Leiden
  • IBL Animal Sciences

Work address

Sylviusweg 72
2333 BE Leiden
Room number 7.4.14


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