The Great Barrier Reef loses its ability to bounce back after disturbances such as bleaching

Prior to the consecutive bleaching events that hit the Great Barrier Reef in 2016 and 2017, the UNESCO World Heritage site two more decades of extensive bleaching over the last two decades, one in 1998 and another in 2002.

The damage caused to the Great Barrier Reef by these bleaching events was worrisome to scientists, and in the meantime, the reef system recovered at a much slower rate than by the past. According to a study published in the journal Science Advances this month, the Great Barrier Reef is losing its ability to recover from disturbances such as coral bleaching, crown of starfish spines and cyclones

. the succession of acute disturbances that the reef has undergone as well as the ongoing impacts of chronic pressures such as poor water quality and climate change, have discovered the researchers. But the authors of the study also argue that effective local management strategies could help restore the reef's recovery capacity.

A team of researchers led by scientists from the University of Queensland (UQ) in Australia found that in 2010 the coral recovery rate in the Great Barrier Reef Marine Park decreased by 84%. % on average

"This is the first time that a decline in recovery rate of this magnitude has been identified in coral reefs," writes Juan Ortiz, of the Australian Institute of Ocean Sciences. and the School of Biological Sciences of the UQ. Sciences, said in a statement. "The future of the Great Barrier Reef is threatened without further local management to reduce chronic disruption and support recovery, and strong global action to limit the impact of climate change."

The team determined that the reduction in average recovery rates of the main coral groups was between 68 and 143 percent. In other words, some groups have moved from positive growth rates to negative growth rates and there has indeed been a net decrease in these types of corals between disturbance events. "Two of the groups of corals – branches Acropora and Montipora – had negative mean recovery rates at the end of the study period," write the researchers in the study. 39; study.

However, in some areas, reefs showed no decline in recovery rates. According to the study: "In most cases, recovery rates were less negatively affected in the Midwest and Swains region [Great Barrier Reef]."

The authors note that the mechanisms responsible for the Great Barrier Reef are slow to recover in recent decades would require large-scale and difficult prohibitive experiments. But they rank a number of causes of the decline in coral growth rates:

"Calcification and growth rates decreased by 14% in some species, as Porites in response to stress thermal increasing. In addition, ocean acidification probably reduced the net calcification of coral reefs in the south [Great Barrier Reef]. Growth can also be reduced for several years after whitening episodes, and some corals mix their symbiotic populations during episodes of heat stress, increasing the abundance of heat-tolerant symbiont types. While these symbionts can tolerate high temperatures, their predominance can reduce up to 70% growth of their coral hosts. "

Professor Peter Mumby of the ARC Center of Excellence for Coral Reef Studies of the UQ, co-author of the The study, said the declining recovery capacity of the Great Barrier Reef is of particular concern.The impacts of climate change on the reefs will only increase with the warming of the oceans.

"Such as" identified in our findings, climate change is already affecting the coral recovery rate in a chronic way and by the effect inherited from acute thermal events. "the team states in the study." Our badysis suggests that recovery rates are expected to continue to decline under climate change and ocean acidification due to impacts on coral recruitment and growth. Thus, we echo many other calls for urgent action to reduce greenhouse gas emissions and maintain functioning ecosystems.

But Mumby also emphasized the importance of the team's conclusion that not all reefs are recovering. He and his co-authors write in the study that while they anticipate that the average coral cover will decline, the striking spatial variability in the recovery rate implies that some reefs will continue to function much better than other species. 39. Others Understanding the causes of this variability is important and will help to target management actions and provision of ecosystem services through the identification of reefs / regions, where the ecological benefits of management action Local may be maximized. "

Mumby said in a statement he believes that there are reasons to hope that improved management can help restore the Great Barrier Reef:" Our Results indicate that coral recovery is sensitive to water quality and is suppressed for several years after strong cyclones. Some reefs could improve their recovery capacity if the quality of the water entering the reef is actively enhanced. The good news is that models have shown that recovery rates can respond quickly to reductions in stressors such as poor water quality. fast observed on some reefs in the central and southern Great Barrier since the end of their study are consistent

"A combination of local management measures to reduce chronic disturbances and global action to limit the effects of climate. it is urgent to make changes to support [Great Barrier Reef] the coverage and diversity of corals, "they write.

CITATION

• Ortiz, J.C., Wolff, N.H., Anthony, K.R., Devlin, M., Lewis, S., and Mumby, P.J (2018). Impaired recovery of the Great Barrier Reef in a context of cumulative stress. Science Advances, 4 (7), eaar6127. doi: 10.1126 / sciadv.aar6127

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