A manipulative field experiment was used to assess the spatial variation in the effect of copper on sessile invertebrates within a marina in Port Phillip Bay, Victoria. Sessile invertebrate assemblages were grown on perspex plates for 6 weeks and then dosed with plaster blocks impregnated with copper sulfate. After 1 week of exposure to the copper the plates were collected and the numbers of sponges, polychaetes, barnacles, bryozoans and ascidians were counted on each plate. The variation in abundances of individual taxa were estimated at spatial scales of metres. Water flow was measured as a possible explanation for the variation in the effects of copper.
Three of the 20 sessile invertebrates species showed significant small scale variation in the effect of copper. The effects of copper on these species varied in magnitude and direction. Water flow did not explain the variation in the effects of copper. It is suggested that variations in organic or inorganic compounds or in pH levels may provide alternative explanations for the spatially variable effects of copper in the marina.