The 27–year decline of coral cover on the Great Barrier Reef and its causes

Abstract

The world's coral reefs are being degraded, and the need to reduce local pressures to offset the effects of increasing global pressures is now widely recognized. This study investigates the spatial and temporal dynamics of coral cover, identifies the main drivers of coral mortality, and quantifies the rates of potential recovery of the Great Barrier Reef. Based on the world's most extensive time series data on reef condition (2,258 surveys of 214 reefs over 1985-2012), we show a major decline in coral cover from 28.0% to 13.8% (0.53% y −1 ), a loss of 50.7% of initial coral cover. Tropical cyclones, coral predation by crown-of-thorns starfish (COTS), and coral bleaching accounted for 48%, 42%, and 10% of the respective estimated losses, amounting to 3.38% y −1 mortality rate. Importantly, the relatively pristine northern region showed no overall decline. The estimated rate of increase in coral cover in the absence of cyclones, COTS, and bleaching was 2.85% y −1 , demonstrating substantial capacity for recovery of reefs. In the absence of COTS, coral cover would increase at 0.89% y −1 , despite ongoing losses due to cyclones and bleaching. Thus, reducing COTS populations, by improving water quality and developing alternative control measures, could prevent further coral decline and improve the outlook for the Great Barrier Reef. Such strategies can, however, only be successful if climatic conditions are stabilized, as losses due to bleaching and cyclones will otherwise increase.

Implications of Australia's Population Policy for Future Greenhouse Gas Emissions Targets

“…Whether Australians choose to limit their future population growth is entirely another matter. The country's natural systems have already suffered severe degradation of ecosystems from forest loss and fragmentation because mainly of past agricultural expansion (Bradshaw 2012), lowered rainfall in some areas because of deforestation (Pitman et al 2004), increasing salinization of agricultural land (Pannell 2001;Clarke et al 2002;Lambers 2003) and freshwater (Nielsen et al 2003) systems because of deforestation, the world's highest mammal extinction rate (Woinarski et al 2015), extensive economic and environmental problems associated with introduced animals and weeds (Bradshaw et al 2007;Bradshaw et al 2013;Gallagher & Leishman 2014;Krull et al 2014) and declining health of its coral reefs (De'ath et al 2012;Hughes et al 2015). In this context, any policy that seeks an even larger Australian population would need to be carefully focused on how to achieve this goal sustainably, while mitigating (and, in some situations, reversing) these threatening processes.…”

Morphological characterisation of reef types in Torres Strait and an assessment of their carbonate production

“…Moreover, the employed regional census-based approach is subject to uncertainties in data and methods and warrants further research. It may be necessary to update and refine these values in the context of reduced calcification due to global trends in coral reef ecological decline (De'ath et al, 2009;De'ath et al, 2012) and increased ocean acidification and sea surface temperatures (Kleypas and Yates, 2009;Silverman et al, 2009). …”

Multiple stressors threaten the imperiled coastal foundation species eelgrass (Zostera marina) in Chesapeake Bay, USA

“…This absence is particularly 44 striking for temperate coastal ecosystems, which, ironically, support much of the world's human 45 population. Instead, most of our understanding of coastal change comes from small-scale 46 experiments and observations (Crain et al, 2008(Crain et al, , 2009), or from tropical systems such as coral 47 reefs (Gardner et al, 2003;De'ath et al, 2012). This knowledge gap vastly impedes our ability to 48 predict and avert the impacts of global change on key population centers, particularly given the fact 49 that stressors, and corresponding management actions, often occur at much larger scales.…”