Analysis of biological traits within assemblages is increasingly used as a proxy for ecological functioning. However, taxa often show plasticity in the expression of traits and can potentially change trait expression depending on local conditions. While many forms of disturbance will lead to changes in the species composition of the assemblage, small-scale disturbances can trigger alterations in the behaviour of taxa and hence the ecological roles they are delivering. Such changes would not be detected by biological traits analysis (BTA) alone. BTA therefore has the potential to misinform as to the contribution of assemblages to ecological processes. To assess the potential for taxa to change their expression of traits, the feeding modes of 8 taxa from 2 intertidal assemblages in north-west England, UK, were investigated using stable isotope analyses following experimental sediment disturbance and removal of cockles Cerastoderma edule. Two of the 8 taxa exhibited significant changes to their isotopic composition within disturbed plots. Short-term plastic changes to food web dynamics following changes in environmental conditions have implications for the suitability of BTA as a tool for investigating ecosystem function. Although BTA provides much insight into the ecological roles of taxa within systems and can be extremely effective at identifying changes associated with different assemblage compositions, it is conceivable that changes to ecological functioning may be undetected by BTA alone, and hence there is the need for this approach to be supported by experimental observation.