Sponges as sentinels: Metal accumulation using transplanted sponges across a metal gradient

To be effective sentinels, organisms must be able to be readily translocated to contamination hotspots. The authors sought to assess metal accumulation in genetically identical explants of a relatively common estuarine sponge, Suberites cf. diversicolor. Explants were transplanted to 7 locations across a metal contamination gradient in a large coastal estuary in southeastern Australia to establish, first, that explants of this species could be successfully translocated; second, that explants accumulated metals (cadmium, copper, lead, selenium, and zinc) sufficiently rapidly to be effective sentinels; third, that rates of metal accumulation in explants were in agreement with metal concentrations within sediments (<63-µm fraction) at each of the transplant locations; and finally, that changes in explant biomass correlated with overall metal load. Suberites were readily transplanted, with no mortality observed for the 2 mo of transplantation. Metal accumulation for lead, cadmium, and zinc was in close agreement with sediment metal concentrations, and explants showed dramatic increases in these metals in the heavily contaminated northern sections of the estuarine lake. No striking patterns were apparent for copper and selenium. Finally, growth was negatively correlated with total metal load and standardized total metal load in our explants. Taken together, these outcomes confirm that explants of this sponge are amenable to translocation and show considerable promise as biomonitors.