SIEVE MESH SIZE AND TAXONOMIC RESOLUTION NEEDED TO DESCRIBE NATURAL SPATIAL VARIATION OF MARINE MACROFAUNA

The effects of sieve mesh-size and taxonomic resolution on patterns of natural spatial variation of soft-sediment, marine macrofauna were ex amined simultaneously over a range of depths and 2 spatial scales. Pre vious studies have considered the effects of mesh-size and taxonomic r esolution separately, mainly for macrofauna exposed to pollution. Mesh -size (0.5 mm or 1 mm) and taxonomic resolution (species or family) ma de little difference to the spatial patterns detected by non-parametri c, multivariate analyses (MDS and ANOSIM) for assemblages of macrofaun a but results suggested that slightly more information was lost by usi ng the coarser mesh than by using the coarser level of taxonomic resol ution. For about half of the populations of individual taxa examined u sing parametric, univariate analyses, mesh-size affected the interpret ation of spatial patterns to some degree. The absolute abundances of s ome other populations of macrofauna were underestimated using a 1 mm m esh as compared to a 0.5 mm mesh but patterns of spatial variation of these families did not vary between mesh-sizes. There were often less than 5 species per family and the spatial variation of the single most abundant species in each family probably dominated the spatial patter ns detected in family-level analyses. For some speciose families (e.g. Spionidae, Corophiidae), however, the spatial variation of particular , relatively abundant species may differ from that detected at the fam ily level. The best way of incorporating rarer taxa into analyses may be multivariate methods which also seemed more robust to coarser mesh- sizes and levels of taxonomic resolution than univariate methods. Samp les of macrofauna sieved through a 0.5 mm mesh took significantly long er to sort to major groups than 1 mm samples. The size of this differe nce, however, depended on the location from which the samples were tak en. Since many more samples can be processed per unit time, coarser me sh-sizes and levels of taxonomic resolution should allow greater repli cation at both large and small scales for macrofauna with little loss of information.