Experimental set-up. Three locations, with a low, medium or high diversity, were sampled and in each location, three Van Veen grab samples (biological replicates A, B and C) were taken. To test the effect of technical replicates on the alpha and beta diversity, six subsamples of each biological replicate were taken for DNA extractions (DNA replicates 1 to 6). In two locations (LOW and HIGH), three separate PCR amplifications were sequenced of one DNA extraction (PCR replicates 1 to 3). To test the effect of pooling multiple DNA replicates, three combinations of two, four or six DNA replicates were pooled before amplification (Pooled DNA replicates for each number of pooled DNA extracts).