Biomass measurements (AFDW) of both subtidal and intertidal macrofauna of the ‘Abra de Bilbao’ embayment were used within a pilot study in a four step strategy of analysis, which consisted of: (1) representing communities; (2) discriminating sites or conditions; (3) determining levels of ‘stress’; and (4) linking to environmental variables. Univariate (number of species, diversity indices) as well as multivariate (clustering, MDS, SIMPER, BIO-ENV) techniques from the PRIMER package were employed. Several data aggregation levels were proposed in the analyses with the aim of selecting cost-effective procedures. The results suggested a good integration of environmental conditions by subtidal samples, which were close to constant on all different taxonomic aggregation levels. The abiotic parameter which best ‘explained’ the biotic pattern of subtidal samples in the investigated area was turbidity measured as total suspension solids and nephelometric units on the water surface. In conclusion, we recommend monitoring rocky substrates by using more extensive biomass sampling surveys of subtidal areas followed by a less time-consuming treatment of the samples (identification by high taxonomic categories or by trophic groups).