Aarhus University Seal / Aarhus Universitets segl

Background & Overview


The Baltic ecosystem has undergone drastic changes over the past century due to a combination of anthropogenic and natural stressors. As is often the case, these changes have been most notably documented in charismatic wildlife species, including grey (Halichoerus grypus) and ringed seals (Pusa hispida), white-tailed eagles (Haliaeetus albicilla) and otters (Lutra lutra). These and many other species have undergone massive population declines in the Baltic, with many factors hypothesized to have played a role. Anthropogenic hazardous substances (AHSs) have shown to be a major force behind the reduced health of the Baltic. Though environmental levels of some AHSs have declined since their international restriction in the 1970-80s, concentrations in high trophic predators of the Baltic remain relatively high compared to other areas. Adding to pollution stress are other anthropogenic stressors, such as shipping and underwater noise, offshore developments, over-fishing, hunting, eutrophication, as well as exacerbating effects of a changing climate and associated altered food web dynamics.

Much of our knowledge of the population-level consequences of AHSs is derived from observations of drastic reproductive effects, especially in the Baltic. Present-day health assessments include aspects of most important physiological systems, including the endocrine and immune systems. We continually improve our understanding of single compound effects on a growing number of biomarkers in wildlife. However, these compounds rarely occur in isolation and relationships with other stressors and risks assessments are challenging to make. At present day, there is few information available to assess the cumulative impact of multiple stressors on single species, let alone the food web. Thus, it is important to understand, identify and quantify powerful indicators of individual, population, and ecosystem health as they allow assessing the impact of multiple anthropogenic and natural stressors over space and time.

The BALTHEALTH project was thus initiated in 2017 as a collaborative effort from multiple Baltic countries to assess the past and current state of the Baltic ecosystem. 



The concept of BALTHEALTH is to provide integrated tools that allow for the assessment of the anthropogenic impacts on the ecological functioning and overall health of the Baltic ecosystem. The project focuses specifically on the impact of AHSs on all levels of the Baltic ecosystem and therefore requires a holistic approach to assess environmental health. Our approach utilizes state-of-the-art dietary tracers and energy/nutrient modelling to assess Baltic food web structure and dynamics, which together with a thorough spatiotemporal analysis of the occurrence of legacy and emerging AHSs will provide understanding of their sources, transport and fate in the Baltic.

The overall objective of the project is to investigate how multiple natural and anthropogenic stressors have been impacting key ecological and commercial species within the Baltic food web, from the individual to the population and ecosystem level. In order to assess cumulative ecosystem wide effects of AHSs on Baltic wildlife, BALTHEALTH will address the following issues:

  • Food web structure and dynamics: The Baltic food web varies spatiotemporally, which has important implications for nutrient, energy and AHS dynamics. 
  • Quantifying important legacy and emerging AHSs: AHSs have many point and diffuse environmental sources and show complex environmental partitioning and cycling behaviour. Furthermore, thousands of new chemicals are produced every year, potentially posing new chemical threats. 
  • Biomarkers of adverse health: The use of biomarkers of effects have been reported scattered across species and locations around the world, though focussed spatiotemporal patterns are rarely reported. Developing new non-invasive biomarker techniques and determining which of these best indicate population and ecosystem-level effects is important for risk assessment.
  • Infectious diseases: The Baltic and neighbouring seas have been a playground for major viral outbreaks leading to the death of tens of thousands of seals over the past decades. It is important to understand pathogen reservoirs, transmission routes and evolution. 
  • Multi-level effects of multiple stressors: While understanding health effects at the molecular, cellular and individual organisation is important, extrapolation to higher organisational levels is often hard to make. Effects of multiple stressors on various levels of the food web are even less often attempted. 

Find more detail in work packages...