Community response to metal pollutants; a field spiking experiment on an estuarine mudflat

Benthic intertidal habitats of estuaries are complex environments and are subjected to pollution from a variety of upstream sources. Determining the impact of a specific pollutant on the structure and function of the benthic... [ view full abstract ]

Benthic intertidal habitats of estuaries are complex environments and are subjected to pollution from a variety of upstream sources. Determining the impact of a specific pollutant on the structure and function of the benthic macroinvertebrate community is problematic due to the changing conditions (such as salinity and temperature) of the natural environment. Field experiments using sediments spiked with pollutants provide the opportunity to understand the effects of specific pollutants under naturally variable environmental factors, while investigating broader ecological impacts; especially factors such as competition, predation and avoidance behaviour. In order to determine if an increase in the concentration of metals within the sediment alters the structure of the intertidal benthic community, direct manipulation of sediments in the field was undertaken. Sediment from Little River estuary (Port Phillip Bay, Victoria) was spiked with copper or zinc chloride at concentrations below levels considered to have deleterious effects (Zn <150ppm, Cu<50ppm), and returned to the field. Macronivertebrates were allowed to migrate/recolonise the sediment over a month before being sampled. Variable metal concentrations were returned from the sediment at the end of the experiment, possibly due to resuspension and deposition of muds. Nevertheless, more species were present in the control or ambient sediment than in those spiked with metals. Total number of individuals was found to be higher in copper spiked sediments compared to control or ambient sediment. Paracorophium spp were also found in greater abundance in sediments spiked with copper or zinc, and this species was the main contributor to the increase in the total number of individuals. These results raise the question as to whether Paracorophium spp are more tolerant to metal pollutants, or are quicker at establishing and flourishing in the absence of competition. Our results indicate that an increase in a single pollutant below what is considered a toxic concentration can cause change to an ecological community.