Marine Populations and Ecosystem Dynamics

Main themes within Marine Populations and Ecosystem Dynamics

DTU Aqua's research into marine populations and ecosystem dynamics studies the processes that dictate the relationship between predator and prey, such as the rate at which individual fish meet each other and individual fish's nutritional requirements for growth and reproduction. These requirements ultimately determine the fundamental energy flows in the ecosystem.

We investigate how fish larvae succeed in becoming large enough to be included as part of a stock, what small fish out in the open sea mean for the ecosystem, and what role plankton plays in the ecosystem. We also look at the sizes of individuals and populations, the number of species and populations, and at how species and populations are distributed in the sea.

As a result of knowledge gained from studying these mechanisms, we are able to develop physical-biological models that can describe and predict the processes affecting individual fish and how these processes can lead to changes in the whole ecosystem. These models need to be able to look at individual fish movements and activities in relation to food and environmental conditions. The models can thus provide the basis for describing the distribution of fish populations in the ecosystem.

Our research also looks at models of entire ecosystems. With these models, we try to describe the current status of and changes in the system using some simple basic principles, such as the relationship between the size of individual fish and their energy consumption.

The different individual, population and system-based approaches all aim to better understand how the impact of human activity interacts with environmental conditions and environmental changes caused by climatic factors.

Research into marine populations and ecosystem dynamics can be divided into four main areas:

• Analyses of fish fry and other small marine organisms:How they are transported and dispersed by ocean currents, and how the fry grow and survive under variable environmental conditions, food resources, and chemical and physical factors.
• Analyses of interaction between species: Individual-based models, multi-species analyses and models, the interaction between predator and prey and the interaction between species.
• Theoretical analysis of the interaction between fisheries, the environment and ecosystems in an ecological and evolutionary context: the importance of fisheries for whole ecosystems and the impact of fishing on fish evolution.
• Analysis of the relationship between climate and ecosystems: Models for describing the climate's effect on important life cycle processes such as growth, mortality and fertility, as well as describing how these processes impact on the dynamics of the ecosystems.

In addition, DTU Aqua develops methods to support the research:

• Ecosystem-based planning and methods for collecting data and for monitoring populations, ecosystems and oceanographic parameters. The data collected is used to test the validity of the models.
• Methods for tagging fish in order to study growth, survival, behaviour and migration. These methods can show the distribution of fish in time and space, and applying the models then makes it possible to predict changes in fish behaviour and distribution in the sea.

Why do we conduct research into Marine Populations and Ecosystem Dynamics?

DTU Aqua carries out research into marine populations and ecosystem dynamics in order to understand the general principles behind ecosystem dynamics and in order to be able to develop models of these ecosystems. 

We study key processes at the individual level and scale up to population and ecosystem levels. As an example, migrations of individual fish become population distributions within the ecosystem. In this way, we gain knowledge about growth and reproduction, the interaction between species, the relationship between predator and prey, the age distribution within each species, and feeding and migration behaviour. We are thus better able to understand current conditions prevailing in an ecosystem as well as future changes to the ecosystem.

In addition to this general understanding of ecological and evolutionary processes, we are becoming better and better at predicting the impact of fishing and climate change on ecosystems.

We work with two types of models:

• Statistical models, which are based on technical data collection from fisheries, scientific expeditions, measurements taken from the sea and climate measurements, and on then integrating this data into ecosystem models.
• Simulation models based on mechanistic causality and validated by experimental studies in the laboratory, in aquaculture and in the field.

Together the two types of models provide a picture of the conditions currently operating in the ecosystems, and can therefore be used to analyse and calculate the consequences both of future environmental and climate changes and of the way we exploit marine resources, including fisheries.

What is the research used for?

The research is used to create the knowledge base to enable us to continuously improve models of ecosystems. The total picture we build up of marine ecosystems informs our understanding of how such ecosystems respond to both human activity and natural forces.

Our research and models thereby generate scenarios and predictions of the impact on ecosystems of the forces of nature and human activity and can be used to design management strategies which take into account the interaction between species and climate change.

We also carry out work which involves applying large climate models locally, and we develop models that can predict the climate's effect on species diversity in fish communities and on important life cycle processes such as growth, mortality and reproduction; this in turn puts us in a position to anticipate expected changes in different ecosystems.

DTU Aqua's expertise in describing and modelling marine ecosystems is used to advise national and international authorities, including the EU and the Danish Ministry of Food, Agriculture and Fisheries.