Food web assessments in the Baltic Sea: Models bridging the gap between indicators and policy needs

Abstract

Ecosystem-based management requires understanding of food webs. Consequently, assessment of food web status is mandatory according to the European Union’s Marine Strategy Framework Directive (MSFD) for EU Member States. However, how to best monitor and assess food webs in practise has proven a challenging question. Here, we review and assess the current status of food web indicators and food web models, and discuss whether the models can help addressing current shortcomings of indicator-based food web assessments, using the Baltic Sea as an example region. We show that although the MSFD food web assessment was designed to use food web indicators alone, they are currently poorly fit for the purpose, because they lack interconnectivity of trophic guilds. We then argue that the multiple food web models published for this region have a high potential to provide additional coherence to the definition of good environmental status, the evaluation of uncertainties, and estimates for unsampled indicator values, but we also identify current limitations that stand in the way of more formal implementation of this approach. We close with a discussion of which current models have the best capacity for this purpose in the Baltic Sea, and of the way forward towards the combination of measurable indicators and modelling approaches in food web assessments.

Global climate change and the Baltic Sea ecosystem: direct and indirect effects on species, communities and ecosystem functioning

“…Changes in primary production will impact interactions between the main trophic levels, i.e. phytoplankton, detritus, zoobenthos, detritivores, benthivores, grazers, zooplanktivores and piscivores (Kiljunen et al, 2020;Kortsch et al, 2021).…”

“…A fairly small number of studies have investigated a period long enough to cover any larger number of NAO periods. Research into the long-term dynamics of the food webs in particular is still scarce (Törnroos et al, 2019;Pecuchet et al, 2020;Kortsch et al, 2021).…”

“…The current models however mostly concern the pelagic ecosystems (e.g. cod-sprat-herring-zooplankton food chain) and there are major gaps for key trophic groups, such as macrophytes and macrozoobenthos (Korpinen et al, 2022) and the microbial food web.…”

“…Such studies would provide a more comprehensive view of the responses of the pelagic and benthic systems to climate change in both the open sea and the benthic system, from bacteria to fish (Kortsch et al, 2021). Also, continuation of both spatial mapping programmes and long-term ecological studies will be crucial for validating experimental results and for developing ecosystem models, advancing our understanding of environmental and meteorological drivers of the Baltic Sea ecosystem on large spatial and temporal scales.…”

Stable isotope analysis in food web research: Systematic review and a vision for the future for the Baltic Sea macro-region

“…Food web research is therefore essential for our understanding of the performance of individuals, species, and the functioning and trajectories of entire ecosystems and provides a foundation for ecosystem-based management (Thrush and Dayton 2010 ). It is also a key component of assessments of environmental status, such as good environmental status (GES), under the EU Marine Strategy Framework Directive (MSFD) Descriptor 4 (EU 2008 ; Korpinen et al 2022 ) or Holistic Assessments of the Baltic Sea (HOLAS) by the Baltic Marine Environmental Protection Commission (HELCOM 2018 ). At the same time, recent analyses have highlighted substantial barriers hampering the systematic application of food web knowledge in practice, one of the main issues being the current lack of synthesis of the large but often scattered knowledge base (Eero et al 2021 ).…”