Sydney harbor's seaweed a deadly diet for sea creatures

Up to three-quarters of the offspring of small crustaceans that feed on a common brown seaweed, for example, are killed when they are exposed to copper at levels found in some parts of the harbour, laboratory and field experiments have shown.

The results suggest that other animals higher up the food chain may be indirectly suffering the consequences of pollution as well, says the study, published in the latest issue of Environmental Toxicology and Chemistry.

Heavy metals such as copper, lead and zinc usually find their way into waterways from stormwater runoff, industrial waters and motorised watercraft.

The University of New South Wales research report is from a team that is mid-way through a harbour-sampling program that has recorded toxic levels of heavy metals such as copper and zinc among the affected brown algae in Rushcutters Bay, near Darling Point, and in Mort Bay around Balmain.

“Marine macroalgae such as brown algae are efficient 'accumulators' of heavy metals and appear to be relatively tolerant to their effects,” says UNSW biologist and research team member, Dr Emma Johnston.

“However, a wide variety of sea creatures that rely on the algae for food cannot tolerate the heavy metals in high concentrations.”

She and her colleagues, David Roberts and Alistair Poore, observed a 75% death rate among juvenile crustaceans when they ate experimentally contaminated brown algae containing high levels of copper. Beds of the same seaweed are important shelter habitats for many small marine creatures.

“Contaminated algae in Sydney Harbour represent poor habitat and we found that fewer animals choose to live on this algae,” says Dr Johnston. “This may have further consequences for animals such as fish that are further up the food chain”