Structural and functional indices show similar performance in marine ecosystem quality assessment

• Functional traits may aid in the interpretation of ecosystem health assessment.
• Diversity indices are still a useful first step in assessing environmental state.
• Functional traits may not be generally useful for routine environmental monitoring.

Reliable ecosystem quality assessment of marine environments is increasingly important due to mounting pressures attributable to human activities. Biotic indices are widely used in studies to describe communities and indicate the ecological state of systems. This study focuses on benthic macroinvertebrate-based biotic indices for the assessment of ecosystem health. Indices used in ecosystem health assessment in the marine environment have mainly focussed on measuring structural components of the system while more recently the measurement of functional components has been highlighted. In this study the performance of traditional diversity indices based on structural components of benthic macroinvertebrate communities, indices developed for the EU Water Framework Directive, and indices which are based on functional biological traits of species were compared. The results indicated that while functional indices may provide a more detailed assessment of the benthic communities than structural indices, the overall outcome is broadly similar for both types of indices. This suggests measurement of functional indices may be unnecessary for routine monitoring purposes, although they may have value in revealing more specific aspects of change in a system.