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.