PhD students

PhD students and projects at DTU Aqua within the research area Marine Populations and Ecosystem Dynamics.

Thøger Engelund Knudsen

Title of the PhD project
Fish migration and ecosystem processes

Supervisors
Brian MacKenzie and Patrizio Mariani (DTU Aqua) and Uffe H. Thygesen (DTU Compute)

Background of the project
Seasonal migration can serve as a strong advantage for many species across large scales of the animal kingdom. The Atlantic bluefin tuna is one such species, and travels vast distances, presumably in search for abundant prey resources. This tuna is of special interest in Denmark, as parts of its population have recently started consistently making the journey from the Mediterranean all the way to Skagerrak and Øresund.

About the project
The general objective of this PhD project is to create one or more models that are able to mathematically describe the existence and evolution of migratory routes in pelagic fish populations. It is possible to mathematically show how migration and its benefits can manifest in the evolution of a species due to natural selection. An individual will to an extent remember successful journeys it has undergone during its lifetime. However, it is poorly understood how this knowledge accumulates and persist, transcending through generations, especially for species without means of explicitly communicating this information. I seek to develop a novel framework that explains the existence and creation of migratory routes in social memory so that we can understand the spatio-temporal dynamics of populations of fish like the Atlantic bluefin tuna.

Perspectives
This project will help determine the key aspects for local populations of Atlantic bluefin tuna, hopefully ensuring that they have come to stay. Furthermore, the existence of a framework that describes the creation of migratory routes through collective behaviour will advance our ability to understand and predict changes in migrational patterns in a changing world.

Yixin Zhao

Title of the PhD project
The role of fish in carbon cycling and the impact of climate change

Supervisors
Ken H. Andersen and P. Daniël van Denderen (DTU Aqua)

Background of the project
The Earth’s oceans play a crucial role in regulating the Earth’s climate system, absorbing approximately 30% of anthropogenic carbon emissions through the physical and biological carbon pump. In the biological pump, carbon dioxide (CO^₂) is initially fixed by phototrophic organisms, forming the foundation of the marine food webs. This fixed carbon can be transported to the deep ocean through particle sinking (e.g., aggregates, carcasses, and fecal pellets), organism vertical migration, and water movement where it can be stored for long periods, ranging from months to millennia. So far, most studies have focused on plankton’s role in the biological carbon pump, while our comprehension of the contributions of fish to the biological carbon pump remains largely uncertain.

About the project
This project aims to bridge this knowledge gap by applying the FishErIes Size and functional TYpe model (FEISTY) alongside earth system models to assess and quantify the role of fish in global ocean carbon cycles, as well as the effects of fishery and climate change. To accomplish the goals, the FEISTY model will be two-way, online coupled with biogeochemical models through the Framework for Aquatic Biogeochemical Models (FABM). We will utilize reconstructed global fishing data with historical fishing patterns and different emission scenarios to force the coupled models, to investigate how fish-mediated carbon fluxes and sequestration vary under various climate change scenarios and fishing scenarios from past to future.

Perspectives
We expect the project to significantly improve our comprehension of fish-mediated carbon flux and sequestration in marine carbon dynamics. We will offer a novel approach to investigating and quantifying fish-mediated carbon fluxes and sequestration through coupling with earth system models. Furthermore, this research will underscore the importance of sustainable fisheries management in maintaining carbon sequestration from fish, thus contributing to climate change mitigation strategies and corresponding policy decisions.