Perspex multiplate artificial substrates were deployed in the Ohinemuri River on two occasions from May to November 1987. A pilot study was conducted to compare the fauna on substrates with that occurring naturally in the benthos, and a second study to investigate the colonisation dynamics. In general, the fauna on artificial substrates was similar to that of natural benthic samples, but with a greater macroinvertebrate density and total taxa number, and dominated by Austrosimuliwn australense and Chironomidae larvae. Colonisation stabilised after 28 days, after which there was little change in diversity. In contrast, equitability decreased, reflecting the greater contribution from A. australense and Chironomidae. There was a steady build-up of fine particulate organic matter (FPOM) on the perspex surface. The relatively low exposure time necessary for equilibrium levels to be reached was attributed to the distinctive characteristics of the New Zealand aquatic fauna. The artificial substrates were slightly more variable in their density estimates than was the natural benthic sampler, but were considered suitable for collecting macroinvertebrates for biomonitoring studies where conventional techniques are impractical or inappropriate, and the stated aims of the use of artificial substrates are clearly defined.

Macroinvertebrate colonisation of perspex multiplate artificial substrates suspended in the Ohinemuri River, New Zealand, was investigated over a 70-day period. Community development was examined in terms of the colonisation and extinction rates of the MacArthur-Wilson equilibrium model for island faunas. Although colonisation and extinction rates were equal at 35 days, permanent stability was not attained: the extinction rate and colonisation rate continued to fluctuate as new taxa continued to colonise. This lack of permanency was attributed to changes to the surface of the plates through increases in the accumulation of fine paniculate matter, and to changes in the drifting fauna that affect the pool of potential colonisers. Stream drift was an important source of colonisers, especially in the initial stages of colonisation. Although many members of the New Zealand aquatic fauna have non-seasonal life cycles, and are present as larvae at all times of year, they may occur seasonally in the drift. Therefore colonisation patterns may differ seasonally. Drift was not the only source of artificial substrate colonisers.