BLUE2 for D1, D3, D4 and D6

How food web models Can Help

These models can help address data gaps and support inference under conditions beyond those directly observed. They can assess:

• Changes in the biomass and abundance of species or species groups (e.g., trophic groups) that are characteristic of a given ecosystem, in response to environmental pressures (e.g., climate change) and anthropogenic pressures (e.g., fishing).
• Changes in catches of commercially important species or species groups (e.g., trophic groups) that are characteristic of a given ecosystem, in response to environmental pressures (e.g., climate change) and anthropogenic pressures (e.g., fishing).
• Changes in species distribution of species or group of species (e.g., trophic groups), in response to environmental pressures (e.g., climate change) and anthropogenic pressures (e.g., fishing).
• Identification of critical/essential hot spot areas, such as breeding /foraging sites, Marine protected areas or Vulnerable areas for key species (e.g., marine mammals, seabirds, turtles, sharks)
• Quantification of the relationship between species, environmental, antropogenic pressures.
• Bioaccumulation of microplastics/contaminants in organisms across food webs

Food web Models: How They Work

The software Ecopath with Ecosim (EwE) is used in the Blue2MF to understand how aquatic ecosystems function and how they may respond to environmental and human pressures. It represents the relationships between different components of an ecosystem—including fish, invertebrates, plankton, fisheries and other key groups—and can be used to explore how changes in factors such as fishing, climate and management measures may affect the wider ecosystem. Ecopath provides a snapshot of the ecosystem and the flows of energy and biomass within it, while Ecosim extends this analysis over time, allowing users to examine changes and explore different scenarios. Ecospace adds an explicit spatial dimension, allowing ecosystem processes, species distributions, fishing activities and management measures to be explored across maps and over different areas. Ecotracer module is designed to simulate and analyze the uptake and transport of contaminants such as methylmercury, radiocesium and microplastic, through the food webs. 

Together, these complementary components provide a flexible framework for investigating ecosystem structure, dynamics and spatial patterns, supporting scientific research, ecosystem assessment and evidence-based decision-making for the sustainable management of aquatic resources. The models have been calibrated and validated using stock assessment and/or survey data and statistics (e.g., fisheries statistics), between the end of 1990s and the 2021 that is used as the reference period (Piroddi et al., 2017; Piroddi et al., 2022; Serpetti et al., 2025a and  Serpetti et al., 2025b)

Modelled-derived ecological indicators (over time and space) produced by these models relate to biomass and abundance, trophic structure, community composition, energy flows, and the relative contribution of different pressures to observed ecosystem changes. Such indicators are particularly useful for complementing monitoring-based indicators, including where observations are limited in space or time, and for assessing changes under different management and environmental scenarios. 

In the context of the MSFD, modelled-derived indicators can support and contribute to the assessment of ecosystem structure and functioning and provide supporting information for evaluating progress towards Good Environmental Status. By linking changes in ecosystem-level indicators to their potential drivers, these can also support the evaluation of management measures and provide a modelling-based evidence base for ecosystem-based approaches to marine management and policy development. 

Lessons Learned

• Coupling Models is Essential: Linking hydrodynamic and biogeochemical models with food web models provides a much more accurate picture of how climate/nutrient variations and top-down fishing mortality interact.

• Bottom-Up Environmental Control: Regional primary productivity and environment (e.g., temperature, salinity and oxygen) set the baseline carrying capacity and spatial distribution for upper trophic levels

• Cumulative Stressors Require Ecosystem-Based Management: Managing single species in isolation is insufficient; policies must account for multi-gear interactions, habitat preferences, nutrient regimes, and spatial conservation priorities.

• Vulnerability of Coastal Waters: Coastal and shelf ecosystems suffer the strongest degradation in terms of biomass and catch reduction under cumulative pressures (fishing, eutrophication, climate change), whereas offshore deeper waters are less impacted 

• Winners and losers: Specific management measures might favor certain species/ species groups, with consequences on the entire food webs. This is due to complex food web interactions, where some species benefit ("winners") while others may suffer ("losers"), influencing the overall ecosystem balance.