Marine Ecosystem Climate Services - Forecasting the marine biological environment
Anna Katharina Miesner, PhD student supervised by Mark R. Payne (DTU Aqua) and Brian MacKenzie (DTU Aqua)
Tremendous advances in observing and modelling of the ocean that have occurred in recent decades: today it is possible to make accurate forecasts of physical oceanographic variables, such as temperature and salinity, several years into the future. However, the next step of converting these forecasts of the physical environment into forecasts of the biological environment, and therefore into variables that are directly relevant for stakeholders and society has yet to be taken. Developing these so-called “climate services” for marine ecosystems represents one of the new challenges in marine science.
During my PhD, I will develop seasonal-to-decadal scale forecasts of marine ecosystem variables for different marine species, such as blue whiting, based on the mechanistic understanding of the species-environment relationship. The aim of these forecasts is to enhance the species monitoring and facilitating its sustainable management. Accordingly, appropriate biological models relating physical and biological variables will be identified or developed and coupled to existing seasonal and decadal forecast systems and their forecast horizon and skill assessed.
However, there is no common protocol for estimating the skill of forecasts of the biological environment, yet. Therefore, building on the knowledge of forecast validation metrics used for example in meteorology and physical oceanography, I will review statistical tools relevant in assessing the quality of forecasts of biological variables important in fisheries science, such as the productivity (recruitment) or distribution of fish.
Copepod life cycles, population dynamics and trophic interactions in marine systems
Floor Soudijn, postdoc working with Thomas Kiørboe (DTU-Aqua) and Ken H. Andersen (DTU-Aqua).
Small zooplanktivorous fish, or forage fish, support the largest fisheries in the world. At the same time, forage fish form an essential element of marine ecosystems as the main food source for large predatory fish, seabirds, and marine mammals. Forage fish are themselves supported by herbivorous copepods, the absolutely dominating group of marine zooplankton. However, it is unknown how copepod dynamics affect the flow of energy from primary producers to forage fish and thus, what drives global scale spatial and temporal patterns in forage fish production. This knowledge gap is a result of a dichotomy in marine science: research focuses either on biochemistry and plankton dynamics or on fish physiology and fish dynamics. Moreover, models of marine food webs typically contain a poor representation of copepods. Therefore, my project aims to predict global patterns in forage fish production by connecting fish and primary producers with the missing link: the population dynamics of copepods. I am planning to develop a phytoplankton-copepod-fish model that focuses on the copepod life cycle, based on a previously developed modeling framework for animals with complex life cycles. Using this model, I want to test the effect of copepod traits, seasonality, temperature and productivity on copepod dynamics and fish production.
Characterization of factors determining the utilization of dissolved organic carbon by bacterioplankton in aquatic environments
Johanna Sjöstedt, postdoc working with Colin Stedmon (DTU Aqua)
Climate change is predicted to result in increased precipitation and enhanced input of terrestrially derived dissolved organic carbon (DOC) to aquatic ecosystems in northern Europe. In aquatic systems one of the largest fluxes of carbon is from the pool of organic matter into microorganisms. However, despite a wide interest in assessing the regulating factors of dissolved organic matter (DOM) bioavailability, it is still to a large extent unknown what mechanisms that control the ability of microorganisms to utilize DOM. The aim of my project is to investigate which factors that are most important for organic matter degradation – diversity of the bacterial community or diversity of the organic compounds. Specifically I will 1) investigate if bacterial utilization of DOM is affected by the chemodiversity of DOM, taxonomic diversity or functional diversity of the bacterial community, 2) study if the functional composition of the bacterial community is defined from the environmental conditions, 3) investigate if threshold concentrations for utilization of DOM in the natural environment is affected by composition and diversity of the carbon sources.
A trait-based approach for predicting fish community structure, function and services under climate change and exploitation
Esther Beukhof (MARmaED Marie Skłodowska-Curie ITN), PhD student supervised by Martin Lindegren (DTU Aqua) and Ken H. Andersen (DTU Aqua)
Marine ecosystems are exposed to both environmental and anthropogenic stressors, e.g. climate change and fishing, leading to concerns about the influence of such stressors on ecosystem processes, goods and services. Traditionally, fisheries management has focused on single species and populations. However, more emphasis is now put on developing management tools that can aid in assessing whole fish communities and their relation to ecosystem functioning. Trait-based approaches are a promising way to increase our understanding of fish community dynamics. Functional traits related to size, growth, diet and reproduction are believed to hold information on how organisms will impact ecosystems with regards to ecosystem functions, e.g. food web dynamics, productivity and fisheries yield.
My first research project will focus on the North Sea fish community. By using international survey data I will investigate the spatio-temporal patterns of several functional traits of fish to see how and if these trends are related to environmental and anthropogenic drivers. Once more understanding of trait distributions and their relation to the environment and fishing activities has been acquired, I will investigate spatial trait patterns on a larger scale to compare across large marine ecosystems worldwide. Because several traits are correlated their interactions on such a scale will be identified as well. Finally, I will use the knowledge gained so far to make predictions of the functional trait composition of fish communities under different scenarios of climate change and fishing, and how different compositions affects ecosystem functions and services.
My PhD project is one out of 15 projects that comprise the MARine Management and Ecosystem Dynamics under climate change (MARmaED) Innotive Training Network funded by the Marie Sklodowska-Curie actions. We will be trained in an interdisciplinary context that eventually aims at increasing our understanding of marine ecosystems and at creating new tools and insights that will enhance ecosystem-based management.
Density-dependent processes in marine fish stocks
Rob van Gemert (MARmaED Marie Skłodowska-Curie ITN), PhD student supervised by Ken H. Andersen (DTU Aqua) and Martin Lindegren (DTU Aqua)
Density-dependent processes are important regulators of natural populations, including fish. All current theoretical and practical work on marine fish populations relies on the assumption that density-dependent processes occur early in life, before maturation and before fishing. This assumption may be correct, but it lacks a theoretical foundation and has only partly been subjected to empirical verification. I will be working on a critical assessment of the existing hypothesis of early density dependence as the central regulating process in marine fish populations. I will develop theoretical arguments for when in life density dependence occurs, seek existing empirical data to throw light upon density dependent processes, and examine what the implications are for current fisheries management and reference points. For this I will be working with a mix of theoretical modelling and analysis of existing data sets.
My PhD project is part of the MARmaED Training Network, an Innovative Training Network funded by the European Commission´s Marie Skłodowska-Curie actions, and consists of 15 PhD students from 8 research institutions. Through this interdisciplinary network of scientists, MARmaED aims to increase our understanding of the complex dynamics of seas and oceans under rapid environmental change and its socio-economic consequences.
Benthic-pelagic energy channels in marine ecosystems
Daniël van Denderen, postdoc working with Ken H. Andersen (DTU-Aqua)
Marine ecosystem production is primarily supported by phytoplankton that forms the base of the pelagic food web and, after sinking to the bottom, may enter the benthic food web (often) as detritus. The contribution of both food webs to fish production may vary largely between ecosystems and will as such support different types of fisheries. In this project, we aim to assess the importance of the benthic-pelagic energy channel for fish production and fisheries catches in relation to different environmental drivers (e.g. changes in primary production, depth). The findings will afterwards be used in a food web model to examine how changes in the relative importance of the pelagic and benthic food web may affect the ecosystem response to fishing of different groups of fish (i.e. demersal, pelagic, demersal-pelagic). The model will describe the dynamics of a benthic and pelagic community and includes top-consumers that couple the communities by feeding on prey from both energy pathways.
Benefits, cost, and tradeoffs of defense mechanisms in marine phytoplankton
Marina Pančić, PhD student supervised by Thomas Kiørboe (DTU Aqua) and André W. Visser (DTU Aqua)
Phytoplankton is a highly diverse group of photosynthetic algae and cyanobacteria, which contributes to approximately 50% of the global CO2 fixation, and at the same time profoundly affects the biogeochemical cycles in the ocean due their requirements for various inorganic elements. The fact that many phytoplankton species coexist in the same space and at the same time on few resources, together with the strong top down selective pressure, demands for identification of the traits that determine their ecological niche. However, the competition-defense tradeoffs are very poorly described and quantified in phytoplankton, yet such tradeoffs are required – and, hence, arbitrarily assumed – in many models to allow the coexistence between many species of phytoplankton. In order to reduce predation from higher trophic levels, phytoplankton has developed a variety of physical and chemical defense mechanisms, and has additionally been found to be highly flexible in traits which affect their edibility. My PhD work aims at identifying and quantifying the tradeoffs of defense mechanisms, initially focusing on the thickness of the silica walls in diatoms, as this morphological trait is known to vary widely among diatom species. The fact that the thickness of the silica shells is a plastic trait and can be induced by the presence of herbivores, allows us to directly quantify associated benefits and cost to organisms by comparing induced and non-induced cells.
Functional diversity in fish communities in relation to ecosystem functioning
Tim Spaanheden Dencker, PhD-student, supervisors: Martin Lindegren (DTU Aqua), Mark Payne (DTU Aqua), and Peter Grønkjær (Aarhus University)
Historically and traditionally, the concept of species has been used as a fundamental unit of biodiversity in understanding ecosystems functioning. However, intuitively, it is not the mere presence or absence of a species, but rather its functionality and interactions within a given ecosystems that determines its role and importance for ecosystem functioning, properties and processes. The functionality of each species in a community can be described through a range of traits, which in turn can be summed up as the functional diversity. Functional diversity has been recognised as a better predictor of ecosystems functioning, both scientifically, politically and in management and conservation. However, the concept is still very abstract and intangible compared to the more simple species diversity, and a series of fundamental challenges still exist within the field of research. My PhD project aims to close some of these gaps by investigating spatial and temporal patterns in functional diversity in marine fish communities on regional and global scales in relation to environmental factors and overall ecosystem functions, such as resilience, stability and productivity.
Plankton Trait Ecology in a Changing Marine Environments
Agnethe Nøhr Hansen, PhD student with main supervisor: André W. Visser (DTU Aqua)
The spatiotemporal heterogeneity of the world’s oceans force marine life to specialize and develop traits that maximize their fitness in the specific habitat they live. In high latitudes the changing seasons influences light availability and turbulence conditions, and nutrient concentration alters as the blooming in spring depletes the nutrient pool. The expertise associated with the traits that increase the competitive ability in the habitat has a cost in the form of trade-offs, as an organism cannot be good at everything. I will set up a mechanistic model that describes how the traits of size, nutrient- and light-harvesting investments develop and distribute as a response to the changes experienced in a seasonal environment, and I will include the trade-offs that are associated with the traits. The model aims at increasing the ability to predict how phytoplankton communities will respond not only to the seasonal fluctuations in the environment but also the long term changes caused by climate change.
Hydrodynamics of small marine organisms
Julia Dölger, PhD-student supervised by Anders Andersen (DTU Physics), Thomas Kiørboe (DTU Aqua) and Tomas Bohr (DTU Physics)
In my PhD project I will investigate marine zooplankton using fluid dynamic and kinematic principles related to their feeding and swimming behaviour and ecological models to investigate their fitness and competition. In particular I would like to understand the distinct gelatinous trait as compared to small carbon-dense body plans and the associated tradeoffs. Therefore I am trying to set up analytical models for gelatinous pelagic tunicates such as the centimeter sized filter feeding salps and compare their feeding efficiency and fitness to unicellular organisms such as choanoflagellates, which have a 100 times larger carbon density and are of much smaller size than the inflated salps. These very different organisms, however, are able to feed on similar submicrometer sized food and can thus compete with each other, whereas flagellates themselves are also part of the salps’ diet. As supplement to theoretical models I plan to measure the feeding currents and swimming dynamics of the modeled zooplankton experimentally using for example particle image velocimetry on living organisms.
The sketch shows a salp (left) with large feeding net (grey), pumping water through its body by muscular contraction and a unicellular choanoflagellate (right), creating a feeding current through its filtering collar by the motion of its flagellum.
Trait-based approaches to phytoplankton communities
Subhendu Chakraborty, postdoc working with Ken H. Andersen (DTU Aqua)
Trait-based models of phytoplankton communities have gained enormous interest in recent years. It has become an important tool to describe the evolution of large assemblages of species with aggregate group properties such as total biomass, mean trait, and trait variance (representing the functional diversity of the community). The size of an individual is considered as a key trait that characterizes its physiology and the feeding ecology. The main theme of my project is to understand how the size of an organism affects its food choice and provides competitive advantage to the organism in a specific environment. My approach is to consider individual-based models where the diversity in organisms is determined by their sizes.
Past and future changes in functional trait diversity
Anna Törnroos guest-Postdoc working with Martin Lindegren, Brian MacKenzie and Ken Haste Andersen
A need to move beyond species richness in understanding patterns and changes of biodiversity has lead to the inclusion of functional diversity in ecological studies. Functional diversity refers to the range, degree and distribution of traits among species in communities and ecosystems. Utilizing multiple traits linked to specific ecosystem functions (such as production and biogeochemical cycling) has proven a successful method for assessing functioning over spatial scales. However, less is known about the temporal variability of functional diversity, which is particularly important if we are to predict future changes in ecosystems. Within this project past and future changes of functional structure and diversity under various environmental and anthropogenic drivers are studied on a community level. The aim is to extend these analyses to encompass multiple trophic levels and thus, focus on the major taxonomic and trophic groups (benthic invertebrates, fish, zoo- and phytoplankton). In this project, the Baltic Sea is used as a case study area, because of its natural environmental and diversity gradients, a well-known biology and ecological history as well as availability of long-term data series.
The project is part of the EU BONUS project BIO-C3 (Biodiversity changes – causes, consequences and management implications), and a close collaboration with Prof. Erik Bonsdorff (Åbo Akademi University) and research group.
Distribution of motile and non-motile phytoplankton across a shelf break and implications for optimal feeding mode of zooplankton
Kasia Kenitz, Postdoc, working with Ken Haste Andersen, Patrizio Mariani, Thomas Kiørboe and Andy Visser
One of the fundamental traits characterising zooplankton populations is their feeding mode. The diverse modes can be distinguished into two types: ambush feeding that captures motile prey, and feeding current feeding that targets mostly non-motile prey. Distribution and abundance of motile and non-motile phytoplankton varies on temporal and spatial scales, reflecting the variability in the physical environment and nutrient availability. Seasonal succession from non-motile phytoplankton dominating the early spring blooms, to motile phytoplankton thriving during the summer stratification, reflects the environmental selection for efficient traits, where the ability of vertical migration is advantageous during the severe nutrient limitation in the upper ocean. On the spatial scales, distinct shifts in the phytoplankton community structure were observed across the continental shelf break. These shifts are associated with a region of strong vertical mixing of nutrients driven by the internal tide. Different types of food source and level of turbulence will modify the choice of zooplankton feeding strategy in order to optimize their fitness through balancing the efficiency of capturing prey and the risk of the predator encounter. The shelf sea environment provides a modelling framework used to investigate potential changes in the planktonic interactions in the regions of contrasting physical environment. The main objective of the project is to simulate the distribution of motile and non-motile phytoplankton across a shelf break and investigate how the choice of the optimal feeding mode of zooplankton changes from the open ocean to the shelf sea.
Diagram illustrating different physical regimes across a shelf break and examples of phytoplankton species that can be dominating in those environments during the summer.
Models for population dynamics in copepods
Sofia Piltz, Post doc, working with Ken Haste Andersen, Thomas Kiørboe, Patrizio Mariani and Andy Visser
Traditionally, differential-equation models for population dynamics have considered organisms as ``fixed'' entities in terms of their behaviour and characteristics, and ignored the physiological changes (e.g., growth in size) during their lifetime. However, there have been many observations of adaptivity in organisms, both at the level of behaviour and as an evolutionary change of traits, in response to environmental conditions. In addition, while many organisms (e.g., ciliates) undergo small physiological changes during their lifetime, some organisms (e.g., copepods) grow through a succession of developmental stages (e.g., egg -> nauplius -> copepodite -> adult) that span over several orders of magnitude in size. Taking adaptiveness and individual growth into account alters the qualitative dynamics of traditional models and is an important factor to be included, for example, when developing reliable model predictions under changing environmental conditions. In this project, we use the mathematical framework of dynamical systems theory to construct models for predator-prey interaction. By carrying out mathematical and computational analyses of the resulting systems of equations, we aim to gain insight into the underlying mechanisms of plankton observations in the presence of adaptivity, growth in body size, ecological trade-offs, and seasonality.
Modelling the role of competition between fish and jellyfish in marine pelagic ecosystems
Nicolas Azaña Schnedler-Meyer, PhD student with main supervisor: Patrizio Mariani (DTU Aqua)
In recent decades, reports of a supposed anthropogenic global increase in jellyfish abundances, and in the frequency and magnitude of blooms has been a subject of strong debate, reflecting a general lack of knowledge about jellyfish population dynamics and their role and significance in marine food webs. Though there has been an increase in our knowledge of the individual rates of jellyfish, the importance of jellyfish predation and competition impacts on ecosystem dynamics is still poorly understood, because jellyfish populations are hard to study in the field. The aim of this project is to investigate the importance of competition between jellyfish and fish for the dynamics of their populations, across different types of jellyfish and along different gradients of environmental conditions. I will work with mechanistic, trait-based population models, where population dynamics emerges from traits, processes and rates at the individual level.
Simple food web containing fish and jellyfish, a copepod and a predatory fish. Copepod illustration from: Ohman, M.D., Drits, A.V., Clarke, M.E., and Plourde, S. (1998) Differential dormancy of co-occurring copepods. Deep-Sea Research II 45: 1709-1740. Cod illustration by H. L. Todd, from George Brown Goode, The Fisheries and Fishery Industry of the United States, (Washington, D.C.: Washington Government Printing Office, 1884), plate 58A.
Copepod gender differences in trade-offs between feeding, metabolic costs and survival
Hans van Someren Gréve, PhD student with main supervisor: Thomas Kiørboe (DTU Aqua)
In order to understand the complexity of marine ecosystems and to generate predictive models recent research has focused on the investigation of fundamental traits and associated trade-offs. However, empirical evidence on the trade-offs associated with the three difference zooplankton feeding mechanisms is still scarce and has mainly focused on females. Like many other animals, the male copepod is typically focused on finding females in order to optimize its chance of reproduction. Therefore he has to sacrifice efficient feeding and increases the risk of predation. My PhD work aims at quantifying copepod trade-offs related to their gender, using representative copepod species for the main feeding mechanisms. I perform experimental work which focusses on the gender-specific feeding efficiency, metabolic expenses and predation risk. The results of this project will provide a gender specific quantification of trade-offs associated the main zooplankton feeding mechanisms and improve our current understanding of zooplankton mediated fluxes.
Traits and trade-offs in zooplankton behavior
Rodrigo Almeda, postdoc working with Thomas Kiørboe (DTU aqua)
Knowledge of zooplankton predator-prey interactions is essential for better comprehension of the factors regulating the structure of marine food webs and therefore, for an integrated understanding of the marine ecosystems dynamics. Traditionally, models of pelagic marine food webs quantify interactions between species or functional types, but attempts to embrace the inherent complexity of marine food webs make these models very complex. An emerging alternative approach, the trait based approach, proposes to replace the thousands of species with organisms that are characterized by a few key traits (i.e. those characteristics/features that are essential to the success - fitness - of an organism) and their associated trade-offs (what are the costs and benefits of a particular trait). The present project aims to experimentally quantify the feeding tradeoffs (i.e., feeding efficiency vs. metabolic cost and mortality risk) associated with the three main feeding behaviors in zooplankton and to construct trait-based models to predict zooplankton trait distributions in the ocean. Overall, the proposed project will increase our ability to understand the factors that govern the structure and function of pelagic food webs, and predict their changes under different environmental conditions, including global climate change scenarios.
Functional trait diversity and the resilience of marine ecosystems
Martin Lindegren (DTU Aqua), Laurene Pecuchet (PhD student), Mark Payne (DTU Aqua), Ken H. Andersen (DTU Aqua)
Anthropogenic impacts, notably biodiversity loss, climate change and overexploitation, threaten the provision of ecosystem functioning and services worldwide. Therefore, maximizing resilience has emerged as a central tenet in ecosystem management. Although theory provides a conceptual basis for understanding the stabilizing role of biodiversity, its applicability to real ecosystems, especially marine areas encompassing complex biotic interactions, variable environmental conditions and vast spatio-temporal scales, is largely lacking. In this project, we aim to investigate the effect of marine biodiversity on ecosystem functioning by focusing on functional (trait-related) aspects of diversity on system resilience. The project will utilize modelling and observational data on marine fish traits and distribution to investigate large-scale biogeographic patterns of functional diversity and investigate and compare regional dynamics across ecosystems of various complexity and diversity, where long-term, high resolution data is available.
A trait based approach to explain the impact of climate change on plankton biogeography
Philipp Brun, PhD student with supervisors : Mark Payne (DTU Aqua) and Thomas Kiørboe (DTU Aqua)
Plankton are ubiquitous in the world’s oceans and build the fundament of marine ecosystems. Through their high abundance and metabolic activity they also strongly affect global biogeochemical cycles and ultimately the climate system. Conversely, the alteration of the biogeography of planktonic organisms in response to climate change has been shown to be among the strongest across all forms of life. Knowing how plankton distributions continue to change in the coming century therefore becomes a challenge of high relevance. My PhD is set up around two key questions: Firstly, I will investigate how accurate future predictions of plankton distributions can be. I will use species distribution models to make projections across time and space and evaluate them with observational data from the past. This investigation will be done for many plankton species, as direction and magnitude of changes in biogeography show considerable species-wise variations. The second question is related to this versatility in distributional responses to climate change: I will try to explain the susceptibility to and direction of biogeographical changes based on characteristic traits of plankton, for instance size, dispersal ability, or mechanisms to avoid unsuitable conditions (e.g. vertical migration). This will be done by using an information theoretic approach and hierarchical statistical models. If changes in plankton biogeography could be explained by traits, we had a powerful approach to estimate changes for the large fraction of plankton species, for which observational data is very limited or not available at all.
A trait-based approach towards a better understanding of benthic-pelagic pathways in marine ecosystems
Laurene Pecuchet, PhD student with supervisors Martin Lindegren (DTU Aqua), Mark Payne (DTU Aqua) and Ken H. Andersen (DTU Aqua)
The energy flow through marine ecosystems may primarily be channelled through a pelagic- or a benthic pathway, or a combination of both. The degree to which marine ecosystems may support the pelagic- or benthic food chain and communities of pelagic or benthic fish has been shown to vary across natural and anthropogenic gradients in external conditions. This project will aim to investigate the two pelagic-benthic pathways, and to better understand their distribution along geographic (latitude, depth) or environmental (temperature, nutrients) gradients at the ecosystem and global scale along with the induced trade-offs (sensitivity to predation, food availability). The project will draw inference based on a wide variety of data, involving e.g., (i) synthesis of previously published studies; (ii) global data bases of occurrence and functional traits of zooplankton and fish and (iii) available scientific surveys of secondary consumers and fish. Furthermore, statistical relationships between key ecological traits and external variables will be investigated using several approaches, (e.g., meta-analysis and mixed linear (non-linear) modelling) in order to derive generic functional relationships valid across species or taxonomic groups. Phylogeny (evolutionary distances between the different species, or gender) could also be used to infer the traits distribution for data poor species and would permit to study the importance of functional diversity in the LME (Large Marine Ecosystem).
Consequences of fishing-induced selection of behavioural types
Lise Marty, Post Doc working with Ken Haste Andersen (DTU-Aqua)
I am interested in the evolutionary effects of fishing in harvested fish populations. Rapid adaptive evolution in response to fishing-induced selective pressure (an elevated mortality often associated with size-selectivity) has been cited as the most plausible hypothesis to explain temporal trends in life-history traits revealed in time-series of phenotypic field data. These changes involve decrease in age and size at maturation, higher reproductive investment, and modification of juvenile growth rates, which together commonly leads to smaller adult size-at-age and can thereby impact stock recruitment due to the effect of body size on individual fecundity. In addition, some behavioural traits, such as activity level and boldness, may also increase an individual probability of capture. Fishing might therefore select against more active and bold individuals, which also tend to be faster-growing and have a higher mortality in presence of predators. This project studies the ecological conditions under which fisheries-induced selection of behaviour affects life-history trait evolution and population-level recruitment. Under natural conditions, differences in reproductive success of behavioural types (bold/shy) should mainly depend on food availability and the density of predators. I use a size- and trait-based approach, in which a stock is defined by its mean asymptotic body size, to model individual life-history and behaviour, and quantitative genetic principles to estimate the rate and direction of trait evolution.
Overwintering strategies of copepoda
Mark Wejlemann Holm, PhD student supervised by Benni Winding Hansen (RUC), André William Visser (DTU Aqua) and Torkel Gissel Nielsen (DTU Aqua)
Copepods are the most numerous multi-cellular organism in the marine environment. Copepods are zooplankton and constitute a primary link between primary producers (phytoplankton) and higher trophic level (e.g. fish). During periods with adverse environmental conditions, in temperate regions during winter, copepods disappear partly or completely from the plankton. Copepods have developed different strategies to cope with winter conditions, these can be divided into three categories; dormancy, production of resting eggs, and winter activity. There is generally lack of understanding of which ecosystems that support these overwintering strategies worldwide. Therefore, the aim of my research is to determine how copepod species with similar overwintering strategies are distributed worldwide. Furthermore, I focus more specifically on species that display winter activity, and to what extent they are able to survive without food. Lastly I focus on the importance of resting eggs for early population dynamics in the beginning of the productive season. By gaining an understanding of what governs population dynamics of copepods, it is possible to develop models that can predict how food webs will be influenced by climatic changes.
Quantifying physiological costs and benefits associated with the "mixotrophy trait" in plankton
Starrlight Augustine, post doc working with Terje Berje (KU), Per Juel Hansen (KU), Thomas Kiørboe (DTU Aqua) and Ken H. Andersen (DTU Aqua)
The general philosophy is to conceptualize mixotrophy as a trait with values ranging from 1 (completely heterotrophic) to 0 (completely autotrophic). A-B represent micro-photographs of two individuals of Phacus who were both observed in same pool (pers. comm. Bas Kooijman 2011, Speuldersbos, The Netherlands). (A) shows an individual without chloroplasts and (B) an individual with chloroplasts. Thus in (A) we see a heterotroph and in (B) an individual who is at least partly autotrophic.This suggests that there are trade-offs associated with "choosing" between strategies. In order to investigate costs and benefits associated with the "mixotrophy trait" I will examine energetic costs associated with investing in cellular machinery involved in photosynthesis (e.g chloroplasts) and/or in heterotrophy (e.g. endocytosis). To this end I will parameterize a Dynamic Energy Budget (DEB ) model to mixotrophs ranging from completely heterotrophic to almost completely autotrophic. The way the DEB model conceptualizes the organization of mixotroph metabolism is illustrated in (C). The arrows represent energy/ mass fluxes and biomass is partitioned into reserve and structure. The light green line on the surface of the cell indicates the assimilation machinery. The way fluxes of different substrate are merged and then assimilated into reserve (grey arrows + red circles) must be idealized in such a manner as to capture the wide range of feeding strategies which occur in reality and so constitutes part of this project. My final aim is to investigate under which environmental conditions different degrees of mixotrophy can occur.
Zooplankton Fluid Dynamics
Navish Wadhwa, Ph.D. student supervised by Anders Andersen (DTU Physics), Tomas Bohr (DTU Physics) and Thomas Kiørboe (DTU Aqua)
My PhD work aims at assessing the tradeoffs associated with feeding and swimming in zooplankton, e.g., copepods which are millimeter sized marine zooplankton. The idea is to combine experimental and modeling approaches to directly assess efficiency, energy expenditure and predation risk associated with the principal feeding and motility modes of zooplankton. We use particle image velocimetry (PIV) to describe flow patterns generated by freely swimming and feeding zooplankton organisms. Further we plan to use dynamically scaled models of zooplankton organisms to experimentally examine propulsion forces and spatial and temporal decay of flow structures under well controlled settings that are difficult to achieve with live zooplankton organisms. We use fluid dynamical models to estimate energetic costs and generalize experimental observations to other types of plankton than those observed. The result will be quantification of the tradeoffs associated with the principal modes of swimming and feeding in zooplankton.
Bifurcation analysis of structured population models
Irene Heilmann, PhD-student with Supervisors Jens Starke (DTU Compute), Uffe H. Thygesen (DTU Aqua), and Mads Peter Sørensen (DTU Compute)
My project is about structured population models and the mathematical solutions that can occur in these models. In structured population models we consider how the individuals in a population are distributed over values of a trait. In this context one of the most important traits for life forms in the ocean is the size of the individuals. When organisms grow from birth to maturation they can cover a large range of sizes and this gives rise to different interactions with the environment and within the population, e.g. smaller individuals will typically need less food. Structured models can exhibit various kinds of equilibriums and oscillating solutions and can also have multiple coexisting solutions. To systematically investigate how these solutions evolve and when new solutions arise as parameters are varied I employ numerical continuation methods that are based on the mathematical theory of bifurcation analysis.
Traits and trade-offs in microzooplankton grazing
Lasse Tor Nielsen, Post Doc working with Thomas Kiørboe (DTU Aqua), Anders Peter Andersen (DTU Physics) and Thomas Bohr (DTU Physics).
My project aims to describe and understand various microzooplankton grazing techniques, and to quantify the advantages and trade-offs associated with each of them. Microzooplankton deploy various prey capture techniques, ranging from single cell predation using some form of ambush feeding, to filtering of water masses followed by collection and ingestion of the prey particles retained. With the former, prey cells are often almost as large as or even larger than the predator, whereas prey cells are typically one order of magnitude smaller than the predator in the latter. While filter feeding is often considered the most effective in a high food environment, it also comes with several trade-offs, including the larger energy expenditure and the elevated risk of predation due to the strong hydromechanical signals produced. The trade-offs will favor different feeding strategies under various environmental conditions. I work with several microzooplankton grazers, with various prey capture techniques, to describe and understand the mechanisms involved, as well as to quantify and parameterize the associated trade-offs. Videomicroscopy, hydrodynamically scaled models, particle tracking and modeling of flow fields are some of the methods that we apply in order to achieve this. Are ultimate aim is to improve our understanding of the spatial and temporal distributions of various feeding mechanisms found in the world's oceans - today and in the future.
Traits for bacterial carbon turnover in the marine environment: chemical complexity meets bacterial diversity
Sachia Jo Traving, Ph.D. student at University of Copenhagen (KU) supervised by Lasse Riemann (KU) and Colin Stedmon (DTU Aqua). Collaborations with Uffe H. Thygesen (DTU Aqua)
My research interests are focused on the marine bacterioplankton and their ability to degrade and take up dissolved organic matter (DOM). The DOM pool and nutrient conditions of an ecosystem are important factors for determining the function and role the bacterioplankton community exerts in the food web. In my project we focus on the function of the bacterial community, by investigating ectoenzymes, substrate utility and activity of the bacterial community and how this relates to the composition of the community and the characterizations of the DOM pool. The project is a mix of field and laboratory experiments and development of trait-based models on theoretical microbial questions. We deploy a range of techniques for these purposes such as characterization of DOM and microbiological and molecular tools for in depth investigations of the bacterial community
Figure A) 3D contour plot of an Excitation Emission Matrix (EEM) of the dissolved organic matter in a sea water sample (C. Stedmon). B) A sample of sea water containing bacteria and viruses stained with fluorescent DNA stain. Foto: L. Riemann.
Trait-based studies of mixotrophy in the marine plankton
Terje Berge, Post doc working with Per Juul Hansen (KU), Thomas Kiørboe (DTU Aqua) and Ken H. Andersen (DTU Aqua)
My project combines laboratory experiments with trait based modelling to obtain a better understanding of why, when and where mixotrophy occurs in the ocean. Our traditional understanding of planktonic ecosystems involves a firm distinction between plant-like phytoplankton and animal-like zooplankton – the photosynthetic phytoplankton uses sunlight and inorganic nutrients to produce the biomass that is eaten by the heterotrophic zooplankton. This view is entrenched in textbooks and dominates mathematical modeling of ocean dynamics (NPZ-models). However, many zooplankton can actually also photosynthesize by the use of ingested chloroplasts, and many photosynthetic phytoplankton can feed on other organisms. The dual source of nutrition seems to provide these mixotrophs with a large competitive advantage relative to specialist phototrophs or heterotrophs. Nevertheless, specialists sometimes dominate ecosystems, indicating important trade-offs associated with mixotrophy.
The image shows mixotrophic phytoplankton cells collectively feeding on a copepodite stage of Acartia tonsa (Berge et al. 2012, The ISME Journal 6)
Trait-based modeling as an ecosystem approach to fisheries management
Nis Sand Jacobsen, PhD student with supervisors Ken H. Andersen (DTU Aqua) and Henrik Gislason (DTU Aqua)
My PhD project aims at quantifying direct and indirect effects of fisheries on fish communities. Fisheries management is moving towards ecosystem-based approaches in fisheries; all components of ecosystems must be taken into consideration when making an impact assessment. The project in particular focuses on interactions between fish, and the trophic consequences of harvesting certain components of the system. It is so far not clear which universal exploitation patterns are most beneficial in terms of: 1) maintaining original community structure, 2) achieving high yield or 3) maximizing economic revenue.
I use a size- and trait-based model to consider both the ecological and economical consequences of different exploitation patterns. The model rests on linking individual processes to the size of the fish, which is considered the most important trait in marine ecology. The linkage ignores the concept of species identity and instead describes a fish community by means of functional traits. The models now exist as a theoretical framework but are not operational as assessment tools in real ecosystems. I wish to develop this general approach to describe concrete ecosystems and examine long-term assessment plans and their indirect effects in global sustainable fishing.
How copepods capture and ingest particles
Rodrigo J. Gonçalves, Post doc working with Thomas Kiørboe (DTU Aqua)
I use a combination of experimental approaches to study the feeding behavior or a copepod (Temora longicornis) and its relation with the prey size. My aim is to understand the mechanistic underpinning for the feeding process to provide input to trait-based models. Understanding how zooplankton feed can be a challenging task, especially because it is difficult to observe with traditional methods. Some copepods for example move their mouthparts faster than any regular video camera can resolve. Therefore we use a high-speed camera to observe the very precise moment when the copepod detect, capture and ingest their prey. We combine this with bottle incubations and particle image velocimetry to gain a better insight of the feeding behavior related to prey/predator size relationships.
Reproductive traits of fish
Karin Olsson, PhD student with supervisors Henrik Gislason (DTU Aqua) and Ken H. Andersen (DTU Aqua)
I investigate reproductive strategies in marine fish and how these strategies are related to environmental factors and physiological traits. Marine ecosystems are highly diverse and fish have adapted to life in a range of different habitats. Reproduction is central to this existence, and understanding which factors influence this, as well as how, is a fundamental aspect of management of marine ecosystems.
I collect data on important life history traits in a broad set marine species and try to identify what factors drive particular strategies. This approach takes into consideration both inherent traits of the species as well as external factors characteristic of the habitat and the ecosystem.
Chemical communication in the pelagic realm
Jan Heuschele, Post doc with Thomas Kiørboe and Erik Selander (DTU Aqua)
My project focuses on the chemical characterisation of copepod sex pheromones and their usage pattern in different groups of copepods. Most organisms have the sensors necessary to perceive and use chemical cues of their environment. While for terrestrial organisms the trade-offs and mechanisms of chemical communication are fairly well known, knowledge about their use in the open ocean remains scarce. Males in several copepod species use female pheromone trails to find mating partners. This knowledge can be used refine the modelling of encounter rates, and thus the prediction of population growth in copepods. Besides mating partners, copepods also have to find food, for which they also seem to use chemical cues that are released from phytoplankton. We therefore also want to identify these feeding attractants, explore their use for copepod aquaculture, and their importance for copepod movement patterns. This project is also part of the IMPAQ project.
Trait-based modeling of trophic chains and seasonal forcing.
Erik Andreas Martens, Post doc. with Ken H. Andersen (DTU Aqua) and Thomas Kiørboe (DTU Aqua)
My research aims at understanding how seasonality and its varying strength along different latitudes affects marine ecosystem structure: how does seasons affect predator-prey interactions in the ecosystem? How do seasonal variations influence overwintering and reproductive strategies of marine species? To answer these questions, I study mathematical models of the trophic chain in marine systems. Rather than employing the concept of species or functional groups, I use a trait-based approach, considering individuals with mechanistically based traits that are described by few parameters. By disposing of the species concept, the trait-based approach arrives at a succinct description with few basic parameters, and sidesteps the complexity trap of species-centric modeling approaches. Further my research advances trait-based methods by extending current models to include seasonal forcing and multiple trophic levels, and in particular to consider all the links ranging from plankton to fish. To obtain an integral understanding of the dynamics of marine ecosystems, it is crucial to include all trophic levels.
Reproductive traits of Arctic copepods
Julie Sainmont, Ph.D. student supervised by Andy Visser (DTU Aqua) and Ken H. Andersen (DTU Aqua)
I model the life history of copepods with particular emphasis on the traits related to reproduction: size at maturation, spawning time, and whether or not to make reserves. I use an individual-based model to explore the consequences of these traits on specie's fitness as a function of the environmental conditions. I am inspired by the three Calanus copepods species that dominate the zooplankton community in the North Atlantic and the Arctic. The species have different reproduction traits (size at maturity and spawning time) to cope with the strong seasonality in food availability displayed in these regions. These traits consist of size at maturity and spawning time. Calanus finmarchicus, the smallest species, uses the incoming food to produce their egg (income spawner), while the biggest species, Calanus hyperboreus, stores reserves which fuel spawning when food availability may be low (capital spawner). The middle size species, Calanus glacialis performs a mixed reproduction strategy, storing some reserves but spawning also during the phytoplankton bloom.
Global zooplankton trait distributions in an ocean ecosystem model
Friederike Prowe, Post doc working with Ken H. Andersen (DTU Aqua), Thomas Kiørboe (DTU Aqua), Andy W. Visser (DTU Aqua) and Mick Follows (MIT)
I use a global ocean ecosystem model to simulate zooplankton communities characterized by two master traits: size and feeding strategy. The traits provide a mechanistic formulation of how zooplankton feed on both the phytoplankton and the zooplankton community based on predator-prey encounters. A changing physical environment, provided by the underlying ocean general circulation model, allows me to investigate biogeography, regional and seasonal differences in community structure and related ecosystem functions. The model generates theoretical predictions of the global distribution of plankton communities driven by our current understanding of traits and interactions. These can then be compared with the few observations available and may serve to assess the role of biology for ocean ecosystem functions and biogeochemical cycling.