Comparisons among colonization of artificial substratum types and natural substratum by benthic macroinvertebrates

A field study was designed to concurrently evaluate differences in colonization by benthic macroinvertebrates on a range of artificial substratum types (single particles of natural rock or clay brick and baskets of natural substratum) after three colonization periods (1, 8 and 29 days). Fauna on the artificial substrata were compared to natural substratum and the effect of natural epilithic cover on colonization by zoobenthos was determined. Densities of total number of organisms and the seven most abundant taxa, total number of taxa and quantity of organic material were greater on the natural substratum than on the artificial substratum types. Relative abundances of taxa on pairs of the artificial substratum types, unlike pairs of each artificial substratum type and the natural substratum, were statistically correlated. Among the artificial substratum types densities of total number of organisms and about one-half of the most abundant taxa, total number of taxa and quantity of organic material were greatest in the substratum baskets. Natural epilithic cover on the single rock particles and substratum baskets affected the densities of total number of organisms and two of the seven most abundant taxa. These taxonomic groups were at approximately two to six-fold greater densities on the substrata with fine sediment. Consistent patterns in densities of the zoobenthos on the substrata were found after each colonization period. In our study all measures of the macroinvertebrate assemblages (densities of each taxon, total number of organisms, total number of taxa and relative abundances of taxa), with few exceptions, were different between each artificial substratum type and natural substratum. This result showed the abundance and composition of the macroinvertebrate fauna on artificial substratum types were different from the natural substratum. Therefore, the choice of using artificial substrata instead of direct sampling of the natural substratum should be carefully made. Among the artificial substratum types relative abundances of taxa were similar on the single substratum particles and substratum baskets indicating single particles instead of baskets might be used to sample the zoobenthos. Investigators should consider the potential effect of the natural epilithic cover of substratum particles on colonization by zoobenthos when choosing the type of artificial substratum.