By Jerri-Lynn Scofield, who has worked as a securities lawyer and a derivatives trader. She is currently writing a book about textile artisans.
Science Advances published a paper this week, Impaired recovery of the Great Barrier Reef under cumulative stress, analyzing the recent decline in corals on the Great Barrier Reef. (The full paper may be found here.)
The paper found that coral recovery declined by 84% between 1992 and 2010, with some key coral types exhibiting close to zero recovery over that time period, while other reefs showed high recovery.
The paper attributed loss in recovery capacity partly to “the cumulative effects of chronic pressures including water quality, warming, and sublethal effects of acute disturbances (cyclones, outbreaks of crown-of-thorns starfish, and coral bleaching.”
Note that the period studied inthis paper 1992-2010– predated the serious back-to-back bleaching events of 2016 and 2017, which killed about half the coral in the 1400 mile long reef, as reported by Motherboard in The Great Barrier Reef Is Losing Its Ability to Recover from Bleaching Events.
Even with the exclusion of that bleaching, the effects on coral recovery reported are alarming, as Science News notes in Great Barrier Reef not bouncing back as before, but there is hope:
Dr Juan Ortiz, lead author from The Australian Institute of Marine Sciences and UQ’s School of Biological Sciences, said that during this time, average coral recovery rates showed a six-fold decline across the Great Barrier Reef.
“This is the first time a decline in recovery rate of this magnitude has been identified in coral reefs,” he said.
Yet the paper also suggested action could be taken to improve recovery of Great Barrier Reef coral:
Modeled projections indicate that recovery rates can respond rapidly to reductions in acute and chronic stressors, a result that is consistent with fast recovery observed on some reefs in the central and southern GBR since the end of the study period. A combination of local management actions to reduce chronic disturbances and global action to limit the effect of climate change is urgently required to sustain GBR coral cover and diversity.
Improving Water Quality
I encourage anyone with an interest in this topic to read the full paper, which is linked to above. While news of the deterioration of the Great Barrier Reef is certainly depressing, what I found most interesting is that the paper’s authors suggested that further decline could be managed by improving water quality.
The ideal would of course be to reduce or indeed offset climate change, but in the absence of action on that front, water quality improvements alone could also improve coral recovery. From the paper:
The decline in average coral recovery rates is cause for concern, particularly in tabular and digitate corals, which play a disproportionately important role in driving reef dynamics . Moreover, with increasing frequencies and intensities of disturbances, any reduction in recovery rate may facilitate the ratcheting down of average reef state. As identified in our results, climate change is already affecting coral recovery rate both chronically and through the legacy effect of acute thermal events. Our analysis suggests that recovery rates are expected to decline further under climate change and ocean acidification because of impacts on coral recruitment and growth. Thus, we echo many other calls for urgent action to mitigate greenhouse gas emissions and maintain functioning ecosystems. However, while we anticipate that average coral cover will decline, the striking spatial variability in recovery rate implies that some reefs will continue to function far better than others. Understanding the causes of this variability is important and will help target management actions and the delivery of ecosystem services through the identification of reefs/regions, where the ecological benefits of local management action can be maximized. A considerable amount of variance was explained by proxies of water quality. Because water quality can be improved through management and policy, and is the focus of continued government investments, its deleterious influence on coral recovery may weaken in future. The emerging picture is one of substantial heterogeneity that requires carefully tailored management interventions and renewed action on global scales (citations omitted).
Or, to put this into more straightforward English, again over to Science News:
Professor Peter Mumby of the ARC Centre of Excellence for Coral Reef Studies at The University of Queensland, said that this was serious cause for concern, particularly given the accelerating impacts of climate change on reefs, but it is important to stress that not all reefs are failing.
“I believe there is scope for management to help remedy the situation,” he said.
“Our results indicate that coral recovery is sensitive to water quality, and is suppressed for several years following powerful cyclones.
“Some reefs could improve their recovery ability if the quality of the water entering the reef is actively improved.”
This suggestion is not an instance of magical thinking. As Motherboard points out:
Indeed, the Belize Barrier Reef was recently removed from a list of endangered ecosystems through active management and progressive conservation policies implemented by the Belizean government. Similar principles could save the Great Barrier Reef as well, but action must be taken soon.
Now, the paper’s authors are by no means suggesting that water quality improvements alone will be sufficient to ensure the future health of the Great Barrier Reef:
Dr Ortiz said that the frequency of acute disturbances was predicted to increase, making careful management key.
“The future of the Great Barrier Reef is threatened without further local management to reduce chronic disturbances and support recovery, and strong global action to limit the effect of climate change.”
Scientists not involved with this study also insist on the importance of tackling climate change, as reported by ABC Science in Great Barrier Reef coral recovery slows significantly over 18-year period:
But trying to improve conditions on the reef without tackling climate change is like putting “band-aids on arterial wounds”, according to James Cook University’s Associate Professor Jodie Rummer, who was not involved in the study.
“We definitely need to be controlling problems with water quality and problems with crown of thorns, but first and foremost we need to deal with the big problem,” Dr Rummer said.
“What it does come down to is warming. Everything else just makes it worse, but warming is the primary concern.”