The impacts of flooding on the high-latitude, terrigenoclastic influenced coral reefs of Hervey Bay, Queensland, Australia

Abstract

This study examines the impacts of an acute flooding event on the marginal, high-latitude, terrigenoclastic influenced coral reefs of Hervey Bay in southeast Queensland, Australia. In January 2011, the Mary River near Hervey Bay experienced its eleventh highest flood on record. The Mary River catchment has been highly modified since European colonisation, and, as a result of heavy rain and flooding, Hervey Bay was exposed to reduced salinity and elevated levels of turbidity and nutrients for approximately 14 weeks. Through the use of photograph transects and point intercept analysis, per cent cover of coral reef benthic communities was measured prior to and just after the flooding event. Sites were located between 250 m and 5 km from the mainland and from 18 to 85 km away from the mouth of the Mary River. Overall, there was a ~40 % reduction in coral cover post-flood, including significant mortality up to 89 % at four of six reefs. Mortality did not vary with distance along the coast from the Mary River, but mortality was found to be highest closer to the mainland, where turbidity and nutrients levels were also the highest. Despite the decades of input of highly turbid and nutrient laden waters from the Mary River, recovery has occurred in the past, and, given the persistence of similar conditions, would be expected to take place again. Climate change predicts increased frequency of severe storms and flooding, and this, combined with elevated sedimentation and nutrients from the highly modified catchment, may reduce these recovery periods, resulting in the deterioration of Hervey Bay reef communities.