Spatially variable effects of copper on sessile invertebrates across a marina

Brief description

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.

Lineage

Maintenance and Update Frequency: notPlanned

Statement: This experiment was conducted on the marina at the Sandringham Yacht Club. Seven plastic panels (600x600x5mm) separated by approximately 5m were hung along a 50m section of the marina. There were 4 roughened black perspex plates (110x110x4 mm) attached to the underside of each panel. Each panel was weighted down with a brick and suspended horizontally in the water column at 2m below the low water mark. Sessile invertebrate assemblages were allowed to develop on the plates for 6 weeks before attaching a copper or control plaster block to the centre of each plate. There were 2 copper and 2 control plaster blocks plates on each of the panels.

The plaster blocks were impregnated with AR grade copper sulfate (copper II sulfate (CuSO4) anhydrous; Sigma) and delivered a localised dose of the toxic copper cation, Cu2+ to the experimental assemblages on each plate. Each copper block was made of 3g from CuSO4 which was completely dissolved in 13ml of deionised water and 15g of CSR dental plaster (Calcium sulfate hemihydrate > 98%). Control plaster blocks were made in the same way as the copper plaster blocks, without the addition of CuSO4. The plaster block mixture was poured into hemispherical moulds (4cm diameter). A 35x5mm stainless steel bolt was immersed head down in the centre of each plaster block. Blocks were left to set for seven days at 30°C.

One week after the application of the copper and control blocks, plates were removed from the field and transported in containers filled with local seawater to a laboratory seawater system. Plates were sampled, without knowing their treatment, using a binocular dissecting microscope. The entire recruitment plate surface was sampled except for the 9cm2 area around the centre of the plate (where the plaster block was located). All individuals were counted and identified to the lowest taxonomic level (species, genus or morphospecies). All recruitment plates were sampled within 1 week of removal from the field. The plaster blocks on each plate were dried for seven days at 60°C and the average per cent weight lost per panel was used as an estimate of water flow across each panel.

Notes

Credit
Australian Research Centre Discovery grant to MJ Keough

Purpose
To assess the effect of copper on sessile invertebrate assemblages over small spatial scales.