Pollutants not the biggest danger to reef after major flood

THE impact of catchment pollutants on the Great Barrier Reef is nothing compared to the devastation caused by a reduction in salinity following major floods, according to CQUniversity researcher Dr Alison Jones, who says major floods are "nature's ground zero".

Writing in the PLOS ONE journal this week, Dr Jones discusses the period of December 2010 when the highest recorded Queensland rainfall associated with Tropical Cyclone Tasha caused flooding of the Fitzroy River in central Queensland.

"A massive flood plume inundated coral reefs lying 12km offshore of the central Queensland coast near Yeppoon, and caused 40-100% mortality to coral fringing many of the islands of Keppel Bay down to a depth of around 8m on some reefs," Dr Jones said.

"The severity of coral mortality was influenced by the level of exposure to low salinity seawater as a result of the reef's distance from the flood plume and, to a lesser extent, water depth and whether or not the reef faced the plume source.

"There was no evidence in this study of mortality resulting from pollutants derived from the nearby Fitzroy Catchment, at least in the short term, suggesting that during a major flood, the impact of low salinity on corals outweighs that of pollutants.

"Not all the reefs were affected and those that were are already showing signs of recovery two years after the flood."

Dr Jones said corals were opportunists that would grow wherever there was suitable substrate, especially when it was covered with crustose coralline algae, and "we have plenty of that here".

"These reefs have been largely shaped by the Fitzroy River having recovered from flood events before," she said.

"We need to recognize that marine ecosystems are not frozen in time, that they are constantly changing in response to their environment and that corals are very clever at survival."

You can read Dr Jones' full report, co-authored with Dr Ray Berkelmans from the Australian Institute of Marine Science, here.