Biomonitors and the assessment of ecological impacts: distribution of herbivorous epifauna in contaminated macroalgal beds.

We determined metal contents of co-occurring algae Padina crassa and Sargassum sp. in Port Jackson (Australia), and relationships between metal levels and the abundance of epifaunal amphipods. Copper, lead and zinc concentrations were amongst the highest yet recorded in these algae. Copper, manganese and lead concentrations were far greater in P. crassa than Sargassum sp., possibly due to the low growth of P. crassa in proximity to contaminated sediments. However, in manipulative experiments the proximity of algae to sediments did not explain these differences. The abundance of herbivorous amphipods correlated negatively with the copper content of P. crassa, but not with the lower concentrations in Sargassum sp. The greater contamination of P. crassa led to patchy distributions of metals in algal beds and recolonisation experiments showed Sargassum sp. acts as a refuge from contaminants for epifauna. The contamination of macroalgae may pose threats to epifauna in harbours around the world.