Numbers of most invertebrates are variable. Processes affecting their abundances operate at many spatial and temporal scales. Documenting biodiversity is therefore made complex and appropriate scales are not obvious. Processes at small scales (e.g., behaviour), intermediate scales (e.g., recruitment) and large scales (e.g., wave-forces) are illustrated here for intertidal species. The information needed to describe patterns of diversity in complex assemblages is defined. A novel method of analysing variability in diversity is described to unravel complexity and to quantify changes and differences in diversity of invertebrates. Without appropriate information, biodiversity cannot be described, let alone explained, managed or conserved.