Effects of reduced water quality on coral reefs in and out of no‐take marine reserves

Amelia S Wenger, David H Williamson, Eduardo T da Silva, Daniela M Ceccarelli, Nicola K Browne, Caroline Petus, Michelle J Devlin

Near-shore marine environments are increasingly subjected to reduced water quality and their ability to withstand it is critical to their persistence. The potential role that marine reserves may play in mitigating the effects of reduced water quality has received little attention. This study investigated the spatial and temporal variability in live coral and macro-algal cover and water quality, during moderate and major flooding events of the Fitzroy River within the Keppel Bay region of the Great Barrier Reef Marine Park from 2007-2013. We quantified the exposure of coral reefs to flood plumes using seven years of remote sensing of water quality and coral reef long-term monitoring data. We used a distance linear model to partition the contribution of abiotic and biotic factors, including zoning, as drivers of the observed changes. Moderate flood plumes from 2007-2009 did not result in coral cover declines on reefs in the Keppel Islands, suggesting intrinsic resistance against short-term exposure to reduced water quality. However, from 2009-2013, live coral cover declined sharply following extended periods of high exposure to turbid, low salinity water from major flood plume events in 2011 and subsequent moderate events in 2012 and 2013. Importantly, the ability of the reefs to cope with moderate disturbances following a major flooding event was lost. Although zone (NTR or fished) was identified a significant driver of coral cover, we recorded consistently lower coral cover on reserve reefs than on fished reefs throughout the study period and significantly lower in 2011. Our findings suggest that even reefs with an inherent resistance to reduced water quality are not able to withstand repeated disturbance events. The limitations of reserves in mitigating the effects of reduced water quality on near-shore coral reefs underscores the importance of integrated management approaches that combine effective land-based management with networks of no-take reserves. This article is protected by copyright. All rights reserved.