PhD students

PhD students within the research area Marine Populations and Ecosystem Dynamics.

Regitze Lundgreen

Regitze Lundgreen

Title of PhD project

Spatial and temporal dynamics of migrations in eastern Atlantic cod

Supervisors

Karin Hüssy and Anders Nielsen

Background

Atlantic cod (Gadus morhua) is one of the most important commercial fishes and has seen an overall decline in stock size recently. This is especially evident in the Baltic Sea which has been characterized by declining oxygen concentrations and increased temperatures throughout the last decades, resulting in a decrease in the extent of cod nursery areas. However, it is unknown how changing environmental and biological conditions might affect migration patterns in eastern Atlantic cod. In order to ensure efficient management of cod populations in the future, it is necessary to understand the temporal and spatial variation in cod migration patterns. 

Project

The main aims of the project are to 1) map migration patterns through time, 2) determine which environmental and biological factors affect migration patterns, and 3) identify how individual cod migrate between locations. In order to resolve this, the project will utilize conventional archival tagging data with information on release and recapture of tagged cod from the 1950-1980s covering the Baltic and the North Sea, and more recent data from DSTs (2000-2010s) covering the Øresund to the eastern Baltic Sea. The environment experienced by individual fish will be examined using otolith microchemistry to study individual migrations. By combining these data sources with environmental and biological databases, migration patterns can be studied in great detail using state-space models and geostatistical methods.

Perspective

The results of this project will improve our understanding of how environmental drivers affect cod migration patterns which is especially important in light of the changing climate. Furthermore, information on the spatial distribution of cod is invaluable for proper management of stocks. 

Louise Flensborg 

Louise Catharina Flensborg

Title of PhD project

Resilience and vulnerability of marine fish communities to change

Supervisors

Martin Lindegren and David Nogues-Bravo 

Background

Policy makers, managers and the general public are rightly concerned that marine ecosystems and the services which they supply are under threat from a range of human pressures, including overfishing and climate change. Ecological resilience is the ability of a system to remain organized around the same set of processes, structures, and functions. Resilience in a system is a measure of how much disturbance the system can buffer without moving into an alternative regime. Our knowledge of resilience and vulnerability of marine fish communities to changes are scarce. Consequently, there is an urgent need for a better understanding of the underlying process contributing to increase ecological resilience. 

Project

In this project, we will use available data on marine fish species abundances and traits to assess, quantify and compare the resilience and stability of marine fish communities across the North Atlantic and North East Pacific following the conceptual framework provided by the cross-scale resilience model. We will investigate how key attributes of ecological resilience (i.e., functional redundancy, response diversity and evenness) vary across marine fish communities, as well as between marine ecosystems in both space and time.

Perspective

This will enhance our current understanding of ecosystem resilience in marine fish communities by quantifying and mapping the extent of ecological resilience in marine fish communities, and by estimating how resilience control fish biomass over time. Furthermore, we hope to help guide future research and conservation effort by providing an assessment, and ranking, of the ability of current marine protected areas to protect fish communities of low resilience. 

Rémy DenechereRémy Denechere

Title of PhD project

How depth and particle flux determine the structure and functions of fish and benthos communities globally 

Supervisors

Ken Haste Andersen and André Visser

Background of project

The fish community is vertically structured and can be described as groups inhabiting layers from the surface (pelagic group) to the seafloor (benthic group). Energy production takes place at the surface with phytoplankton and is spread into the ecosystem through two energy pathways, the pelagic (trophic interactions) and the benthic (sinking carbon particles). The depth and primary production together determine the strength of vertical overlapping between the fish groups and therefore the fluxes of energy among the ecosystem. We expect these two drivers to structure the ecosystem. 

About the project

The aim of my PhD is to develop a model capable of describing the vertical structure and the biomass of the fish community using two environmental variables: depth and secondary production. This model rests on a trait-based approach assuming that fish are split into functional groups with specific traits related to depth. 

Perspective

This project would inform us about how fundamental processes contribute to explain the structures of the ecosystem. Apart from this very fundamental aspect, this model can find applications to current challenges. For instance, how does mesopelagic fishing ultimately affect carbon fluxes or pelagic fishing?

Christian Kiær

Christian Mathias Rohde Kjær

Title of PhD project

Marine ecological prediction and climate services

Supervisors

Stefan Neuenfeldt and Mark Payne

Background of project

Due to recent advances in ocean observations and modelling, today it is possible to make forecasts of the physical variables in the ocean on seasonal to decadal time scales. Using better observational data and more skilful forecasts of the physical environment can improve our understanding of the biological environment, leading to models predicting and forecasting ecological changes. Forecasting ecological changes, from productivity to distribution, can provide valuable information for stakeholders and decision makers and developing these so-called “climate services” for marine ecosystems represents one of the new challenges in marine science. However, current marine ecological forecast products are limited to predictions of phenology or distributions: There are currently no marine fish productivity forecasts.

About the project

Traditionally fish recruitment modelling is stock-based, where a single stock- recruitment relationship model is fitted for each stock and rarely incorporates environmental effects. However, the main drivers behind biological processes can change on a yearly basis. Other disciplines have incorporated techniques, such as iterative updating, non-stationarity and multi-model ensemble approaches, which can be adopted by recruitment models. This project attempts to combine the above, possibly resulting in a better understanding of the drivers behind recruitment dynamics. Most importantly, it can also pave the way to operational recruitment forecasting for use in fisheries management applications.

Perspective

The aim of this project is to provide a better understanding of the dynamics and main drivers of fish recruitment. Furthermore, forecast products will be made available for important fish stocks, to provide advice for stakeholders and managers.

Kjetil Thorvaldsen

Kjetil Thorvaldsen

Title of PhD project

Improved methods for detecting population dynamics of mesopelagic fishes using advanced hydro-acoustic methods

Supervisors

Stefan Neuenfeldt, J. Rasmus Nielsen and Patrizio Mariani

Background of project

Mesopelagic fishes are ubiquitous to all world oceans and have been estimated to hold an enormous potential biomass. These fishes have a low trophic level, which makes them a potential sustainable source for protein. But the knowledge on these layers of organisms is limited due to inefficient sampling methods. Mesopelagic fish have been observed to be inefficiently sampled with midwater trawls. There are also several challenges with traditional acoustic observation technologies. Problems such as swim-bladder resonance during acoustic surveys, inclusion of gelatinous zooplankton with similar acoustic properties. With new technologies, such as acoustic wideband systems and optics, there is great potential to learn more about these organisms. 

About the project

In this project, different types of state of the art hydro acoustic and video equipment will be used to observe mesopelagic fishes and other components in the mesopelagic layers. The frequency spectrum of single targets will be used to identify different acoustic classes in scattering layers. Small and large scale behavior will be observed to learn more about the components of the layers, the movement of mesopelagic fish, and interactions with other trophic levels. 

Perspective

This study will highlight the importance of using wideband acoustics on resolved single targets to identify and learn more about the small fishes at great depths. An effort will be made to find a way to separate between mesopelagic fishes and other scatterers. This project will look at different individual fish behaviors. By using target tracking, this study will explore the spatial behavior of mesopelagic fishes and observe interactions with other trophic levels. Mesopelagic fishes are important in the marine foodweb, and such small scale interactions are the basis to understanding the formation of meso- to large scale patterns.

Magnus Heide Andersen

Magnus Heide Andreasen

Title of PhD project

Global change and gelatinous zooplankton: Mechanisms and responses of jellyfish population dynamics to global change induced stressors

Supervisors

Cornelia Jaspers, Mollie E. Brooks and Mark Payne

Background of project

Gelatinous zooplankton organisms are a diverse group of soft bodied, transparent organisms that comprise members from diverse phyla in the animal tree of life. They commonly attract large public attention partly due to their bloom and bust population dynamics, partly due to their interference with human activities especially in coastal waters. It has been suggested that their abundances are on a rise due to global change induced stressors. However, the data and experimental basis to support this hypothesis remains inconclusive.

About the project

The aim of this PhD project is to address the hypothesis that gelatinous zooplankton biomass is increasing due to global change induced stressors from a time series as well as experimental perspective. The project will combine statistical modelling with laboratory-controlled experiments.

Perspective

The results are expected to further our understanding about gelatinous zooplankton’s long-term abundance fluctuations, their underlying population dynamics and the response of certain sub-populations to global change induced stressors.

Amalia Papapostolou Amalia Papapostolou 

Title of PhD project

Trophic efficiency of the pelagic food chain 

Supervisors
Ken Haste Andersen, André Visser and Camila Serra-Pompei

Background of project

The structure of the marine food web plays a crucial role for fisheries and ocean biogeochemistry. Food webs consist of interconnected food chains and in the ocean a food chain typically follows the sequence: phytoplankton, herbivorous zooplankton, carnivorous zooplankton, upper trophic levels (i.e. forage fish). It can take a varying number of steps within a food chain for energy to transfer from phytoplankton to fish across different oceanic regions, depending on the planktonic community composition. The length of the food chain is tightly linked to the concept of “trophic efficiency”, namely the efficiency with which energy flows from one trophic level to the next through predation.

About the project

The aim of my PhD is to make global estimates of the ‘microbial’ trophic efficiency from phytoplankton to small pelagic fish; basically how does energy flow across the food chain. This is crucial to improve our estimates and predictions for fisheries yields and carbon export. To do so, I will explore the mechanisms that govern marine food web dynamics through trait-based modeling, by implementing and further developing the “NUM” model framework, created at the Center for Ocean Life. NUM is a mechanistic size- and trait-based model along the Nutrient-Unicellular-Multicellular axis, based on individual-level processes. In NUM, the multicellular component encompasses ontogeny and describes the population dynamics of key copepod groups, characterized by their adult size and feeding mode. The composition of the plankton community is an emergent property of the model, resulting from predation and competition. 

Perspective

With this PhD, we expect to identify the main mechanisms linking higher trophic levels, such as fish, to primary producers, and see how trophic efficiency correlates to fisheries yields and carbon export.

Marcel Montanyes SoleMarcel Montanyès Solé

Title of PhD project

Marine fish diversity patterns, drivers and underlying processes: present status and predictions under climate change

Supervisors

Martin Lindegren and Ken Haste Andersen

Background pf PhD project

Marine ecosystems and the services they provide are nowadays threatened by several pressures such as climate change, overexploitation of species, habitat destruction, and invasion of alien species. These pressures are likely to negatively affect taxonomic and functional diversity of marine habitats. Failing to identify future biodiversity trends and thus, to tackle the necessary management and conservation actions, will most likely lead to important biodiversity losses. 

About the project

This project aims to study the effects of climate change and other human activities (e.g., fishing) on the past, present and future distribution, composition, and diversity of marine fish communities throughout the North Atlantic and North-east Pacific oceans.  To achieve this overall aim, we also need to better understand the underlying responses of species to drivers and to key the assembly processes that shape the taxonomic and functional structure and composition of communities at different spatio-temporal scales. We will use available data on marine fish species occurrences and traits and environmental variables to build models that will allow us to study the above-mentioned subjects.

Perspective

This project will improve our understanding on the relative importance of the assembly processes and human activities in defining the fish community. Moreover, the study of biodiversity patterns and drivers will allow us to better understand how they will be affected by climate change, so knowledge can be translated into effective management and conservation measures that seek to preserve biodiversity and hence, human well-being.

Toni Vivo PonsToni Vivó Pons

Title of PhD project

Trends and projections in invasive ecology: how susceptible to invasion are our marine ecosystems

Supervisors

Martin Lindegren, Patrizio Mariani and Cornelia Jaspers                                                                                    

Background of PhD project

The spread of non-indigenous marine species has been increasing over the last decades, having severe effects on the functioning of recipient ecosystems as well as a socio-economic impact. Studying biological invasions from a trait-based approach is really interesting to start addressing interactions between introduced and native species from recipient communities, as the functional similarity between non-indigenous and native species coupled with the community assembly rules (environmentally or biologically filtered) play a major role on the invasion success. As a quick example, within an invasion scenario, a greater trait similarity could imply stronger competitive interactions between natives and invaders that could either difficult the invader establishment or be detrimental for native species.

About the project

As a starting point the functional similarity between native and non-native organisms will be assessed, observing if the patterns of similarity are conditioned by the spatial scale, environmental or biotic conditions. This will be done by applying novel techniques for species modeling, which could allow to observe how species are associated by their traits or given certain environmental conditions. Then, the potential consequences derived from the differences in functionality between natives and non-natives will be addressed for recipient communities, e.g. the displacement or enhancing of certain native species, changes in ecosystem functionality or naturalization of the non-indigenous species.

Perspective

The main goal of this project is to propose a trait-based framework to study and better understand how native and non-indigenous species interact and which consequences  these interactions could have on recipient communities. The results obtained could be really useful to expand knowledge about biological invasions in marine environments, and then transferred to policy makers to enhance the conservation efforts towards ecosystems under a biological invasion or more susceptible to be invaded in the future.

Previous PhD students (since 2000)


Peter Fink-Jensen

Stock structure and connectivity of capelin (Mallotus villosus) in Greenland: Otolith microchemistry used to track past whereabouts of a small, pelagic fish
Go to DTU Orbit to download thesis

Camila Serra Pompei

Trait-based models of plankton communities: from individuals to ecosystem functions
Go to DTU Orbit to download thesis

Neil Maginnis

The biogeography of Scleractinian reef corals: evidence from beta diversity
Go to DTU Orbit to download thesis

Aurore Maureaud

Biodiversity-ecosystem functioning relationships in marine communities, Evidence from large-scale observations and modeling
Go to DTUOrbit to download thesis 

Trondúr Jónsson Kragesteen

Lice Management in Salmon Aquaculture, Using the Faroe Islands as a case site
Go to DTU Orbit to download thesis