More than thirty years of data at two benthic stations in the North Sea show periods of stable species composition with decadal shifts. This paper examined the extent to which these shifts alter ecosystem functioning and hence provision of ‘ecosystem goods and services’. Ecosystem functioning results from the biological activity of the organisms present and changes in the life style, behaviour and morphology of the species present at a site alter system functioning. As an exploratory technique, the biological traits composition of the species primarily responsible for the shifts in assemblage composition at the two stations were scored using ‘fuzzy coding’ and the resulting ‘traits’ were analysed multivariately and as time series of both trait composition and function delivery. The traits scored were mapped to deliver of the ecological functions of fish food, carbon cycling and nutrient regeneration. The range and abundance of traits in the assemblage showed only limited temporal variability. This reflected dominance of polychaetes, bivalves, amphipods and ophioroids throughout the series although species composition changed. However, the estimated quantity of ecosystem functions delivered did vary over the study period as a result of changing density of infauna. Thus there is the potential for species substitutions to maintain ecological functioning in marine benthic systems since the decadal scale fluctuations in the abundance and composition of the fauna has altered the quantity/rate of ecological processes over time.