Field Collection
Bivalve shell assemblages were collected from 16 beaches across the eastern coastline of Australia (Fig. 1) in August of 2018 and 2019. Beaches were selected to be evenly distributed along the eastern coastline, eastwards facing and completely open to the ocean. Ten samples were taken from each beach using 0.25 m2 quadrats: five samples were taken north of the beach midpoint and five were taken to the south. Sampling was only carried out during clear days not following a storm to avoid artefacts of depositional changes. Quadrats were randomly placed along the beach between the high and low tide marks, ensuring they were ≥ 10 m apart.
Sediment taken down to a 5 cm depth within each sample was processed through 16-, 8-, and 4-mm sieves, with all shell material retained. Valves that were 70% complete and identifiable to species level were identified and counted. A full list of species and taxonomic authorities used for identification is available as Supplementary Material (Data S1).