PhD students

PhD students within the research area Oceanography.

Kristian MaarKristian Maar


Title of PhD project

Ecology and fluid dynamics of aquatic suspension feeders

Supervisors

Thomas Kiørboe, Anders Peter Andersen and Uri Shavit

Background of project

Aquatic suspension feeders span from unicellular organisms to the blue whale and are characterized by variou mechanisms of filtration, which enable them to separate and retain particles of food from the water. The ocean is nutritionally dilute and marine suspension feeders must therefore be highly efficient in order to successfully capture enough food to grow and reproduce. The biomechanical adaptations suspension feeders have evolved to solve this problem are as diverse as the community of suspension feeders themselves and is fundamentally constrained by physical properties e.g. the size of the filter feeder and the type and size of particle they capture. The flow generated by active suspension feeders also affects their local environment and is theorized to facilitate the aggregation and sinking of marine snow.

About the project

The first part of my project focuses on the fluid dynamics of suspension feeding in sessile barnacles. To determine the flow field generated by barnacle suspension feeding I will use high-speed video and Particle Image Velocimetry (PIV). The second part of my project focuses on the impact of colonization of microscopic suspension feeders on the formation and sinking of marine snow. I will quantify this phenomenon by conducting experiments comparing aggregation and settling of marine snow with and without active suspension feeders.

Perspective

Elucidating the mechanics of suspension feeding provides novel insight into predatorprey relationships and specific solutions to complex fluid dynamic problems. Biomimetic efforts inspired by marine suspension feeders have already yielded technological advancements in industrial filter technology and is currently being discussed as potential solutions to microplastic in the ocean. Understanding the processes of marine snow formation will also increase the predictive power of carbon pump models and contribute to the detailed understanding of sequestration of carbon in the deep ocean.

 
 
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

Torkel Gissel Nielsen & Mollie E. Brooks

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.

 

Delove AsieduDelove Abraham Asiedu 


Title of PhD project

Effect of anthropogenic stressors on the planktonic food webs in the Arctic seas 

Supervisors

Marja Koski and Sigrún Jónasdóttir

Background of project

Recent reports suggest that marine ecosystems worldwide are increasingly exposed to overexploitation and pollution from heavy metals, petroleum, plastics and persistent organic pollutants. In addition, the UN's Intergovernmental Panel on Climate Change has reported that the temperature of the ocean is likely to increase by ~1-6˚C by the end of this century, with fastest-warming occurring in the Arctic areas. We, however, lack understanding of how key organisms (both native and non-native), from primary producers to higher trophic levels, are impacted by climatic and non-climatic changes and how the individual responses of species influence trophic interactions and community structure. This is particularly urgent for Arctic marine ecosystems because they are highly vulnerable to warming due to ice acting as the vital ecosystem element. 

About the project

This PhD project will combine field and experimental studies to quantify the zooplankton community composition and production in the Arctic and their sensitivity to the combined effects of climate change (e.g., increasing sea surface temperature, decreasing salinity and turbidity) and pollution. The zooplankton will consist of both native and non-native species, thus including aspects of the potentially different environmental tolerance of these groups. Also, special focus will be on small (≤ 1 mm) under-studied copepod species that dominate the abundance of Arctic zooplankton at many locations and seasons.

Perspective

The project will provide novel knowledge on the mechanistic impacts of stressor combinations on native, non-native and small under-studied zooplankton species at different ontogenic stages of development. This will contribute to the general understanding of how individual tolerances accumulate to community-level stressor responses, which is essential knowledge to be able to predict the effects of environmental change in the vulnerable Arctic ecosystem.

 

Federica MianoFederica Miano


Title of PhD project

Fluid dynamics, ecology, and evolution of flagellate foraging

Supervisors

Thomas Kiørboe, Seyed Saeed Asadzadeh and Anders Andersen

Background of the PhD project

Flagellates represent highly relevant species among eukaryotes both from evolutionary and ecological perspectives. They are found among all the branches of the eukaryotic tree of life, with highly diverse flagellar arrangements and resource acquisition modes. Also, they play a crucial role in the biogeochemical cycles of the global ocean. Their key position in the microbial food web is governed by their feeding on bacteria and other picoplankton, by their photosynthetic activity, and by themselves being grazed by predators. Their degree of success in eating without being eaten is the key to understand the functioning of predatory flagellates. Their feeding activity dangerously ex-poses them to rheotactic predators that are sensitive to flow disturbances. Therefore, flagellates have evolutionarily developed singular behaviors in terms of feeding modes and predator avoidance, to find an equilibrium between resource acquisition and predation risk. These trade-offs are still largely unexplored among flagellates.

About the project

During my PhD, I will study representative flagellate species belonging to different branches of the eukaryotic tree of life to look at their behaviors both as predators and prey. Firstly, I will investigate escape responses from predators feeding currents to understand their propulsion mechanism that leads to very fast and long jumps, and characterize the fluid signals that elicit them. Secondly, I will quantitatively investigate the kinematics and 3-dimensional beat patterns of diverse flagellar arrangements and use them as input to CFD models to quantify foraging-predation risk trade-offs.

Perspective

My PhD project aims at describing these trade-offs quantitatively and at understanding how they are differently optimized among flagellate species. This is crucial because the diversity of eukaryotic microbial communities is determined by such trade-offs in concert with environmental constraints and microbial diversity in turn governs the functionality and “services” of microbial communities and so their role in ocean biogeochemistry. 

 

Caroline GjelstrupCaroline Gjelstrup

Title of PhD project

Changing oceanographic conditions of East Greenland and its link to regional fisheries

Supervisors

Colin Stedmon, André Visser and Jesper Boje 

Background of PhD project

Knowledge of oceanographic conditions and their variability is essential for assessment of environmental impacts on biological communities, ecosystem services and regional climate variability. East Greenland is a region of both climatic and ecological importance, providing a connection between the Arctic and Atlantic oceans as well as eco-system services such as carbon sequestration and fisheries production. The region is influenced by cold fresh waters from the Arctic and warm saline waters from the Atlantic divided by a continuous front extending along the shelf-break. Oceanographic fronts are often associated with elevated plankton production due to entrainment of nutrients enhancing phytoplankton growth and zooplankton grazing, which supports pelagic and demersal fish. Ongoing Arctic climate change, including diminishing sea-ice cover, increasing discharge from the Greenland ice sheet and anomalous warm water pulses of subtropical origin propagating through the region, alter the physical environment. 

About the project

This PhD project aims to improve our understanding of variability in oceanographic conditions in East Greenland, and how this relates to ecosystem change and fisheries productivity. A combination of in-situ and remotely sensed observational data will be used to characterize oceanographic conditions and resolve underlying mechanisms responsible for variability herein. Eventually, a trait-based model will be applied to understand how changes in environmental conditions influence ecosystem function.

Perspective

By gaining insights as to how the spatiotemporal distribution of water masses in the East Greenland region are changing, and what that change implies for nutrient availability and plankton dynamics we can begin to foresee how East Greenland will respond to future change.

 

Athanasios KandylasAthanasios Kandylas

Title of the PhD project
Carbon sequestration and oxygen minimum zones

Supervisor
Andre Visser & Ken H. Andersen

Background of PhD project
Oceans play a crucial role in regulating and stabilizing the Earth’s climate having stored nearly 40% of the anthropogenic CO2 emissions since the industrial revolution. However, potential tipping points might lead to abrupt changes of critical physical and biological processes affecting important marine ecosystem services, such as carbon sequestration and food production. Even though the science around the physics of climate change is robust, our understanding about the response of the marine ecosystems to these changes is still incomplete.

About the project
The aim of this PhD is to develop a framework through advanced ecological modelling which will be able to give an insight into the ecological state of the majority of the marine ecosystems around the world. We expect that at the end of this process, we will have gained a better understanding of two important and interrelated phenomena: Carbon Sequestration and Oxygen Minimum Zones (OMZ) in the ocean. To accomplish this, the Nutrient – Unicellular – Multicellular (NUM) framework and the SISSOMA, a specialized aggregation model, developed in the Centre for Ocean Life will be applied.

Perspective of the project
Overall, in a fast-changing world we need to be able to make accurate predictions about the function and structure of marine ecosystems on a global scale. The tools developed in this project work on this direction and they will hopefully help us to take critical management decisions on time.

 

Previous PhD student (since 2000)


Gunaalan Kuddithamby

Microplastics in marine waters and their potential risk to marine plankton

Sei Suzuki-Tellier
Feeding mechanisms in phagotrophic nanoflagellates. Predation in the Low Reynolds Number World
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Anders Dalhoff Bruhn

Terrestrial and coloured dissolved organic matter in Arctic waters: Towards in-situ sensor based monitoring of Arctic-Atlantic organic carbon exchange at major Arctic gateways
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Josephine Grønning

Defence in diatoms: mechanisms and trade-offs
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Rocío Rodríguez Torres

Ingestion and effects of microplastics on marine planktonic food webs
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Mads Rode

Physics of microbial feeding. Studies of feeding flows near surfaces, ciliate filtration, and non-intrusive tethering of microswimmers
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Frederik Ryderheim

Opening the black box on predator-induced phytoplankton defenses: mechanisms, traits, and trade-offs
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Jérôme Pinti

Vertical Migration: Structure and function of pelagic ecosystems
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