The Commission Decision 2010/477/EU established three criteria and three indicators to assess food webs status:
 
The definitions varied enormously in their content and level of detail. MS reported a number of methods per indicator and criteria. The most frequently reported methodologies for D4 were:
  • Reproductive performance (success, ability, rate) of bird, marine mammals, etc
  • Biomass and abundance of higher trophic level
  • Structure of population of main trophic group
  • Different measures or indices related to the proportion of large fish (by length or weight)
  • Proportion of fish at the top of the food web
  • Abundance and biomass of different components of the food web (zoo, fish, dolphins, sharks, birds)
  • Analysis of size structure of fish populations
  • Species/specific trends in relative abundance of species
  • Composition of phyto and zooplankton assemblages
In April 2014, ICES facilitated a Workshop to develop recommendations for potentially useful food web indicators (WKFooWI). The workshop built on progress already made to support Descriptor 4 through a joint JRC/DG ENV task force ( MSFD Task group 4 Report "Food webs" (2010)) and the findings from the first implementation cycle. The main findings and recommendations of this workshop are publically available:
Additionally, the DEVOTES FP7 project has developed a software tool to help selecting indicators for the MSFD: the DEVOTool. Among the list of scientific indicators compiled, several are potential tools that can be used to assess environmental status under D4.