2015 – 2017 Global Coral Bleach Event

You’ve probably heard in the media about coral bleaching and may be wondering if it will affect your visit to the reef.  Since April 2016 we’ve been providing updates on the areas we visit.  Until July 2018 these were kept here in chronological order but are now consolidated.

2015-17 bleaching event

The effects of bleaching in 2016 and 2017 are best summarised by GBRMPA.  Boulder corals have not been impacted in the areas we visit, and also soft corals have been little affected.  Plate corals, digitate corals and staghorn (Acropora) corals have been impacted the most, with higher mortality in very shallow areas, especially where the reef topography creates areas that get extra warming on hot days and slack water. Since April 2017 there has been a steady recovery which can be seen by large numbers of new colonies.

We’re very fortunate at Wavelength in having a broad range of sites so we can still visit numerous areas where the reef appears little affected. However, there are places offshore this coastline where the level of coral mortality that occurred in 2016 and 2017 was shocking – and it was worse further north over a vast area to the northern tip of the GBR.  Our passengers are still having a great experience and impressed with the coral, and there are a large number of young corals growing.  That shouldn’t confuse how serious this bleaching event was. Coral reefs worldwide have been badly impacted, following the same pattern as the previous strongest recorded El Nino event in 1998, except more severely.  Very strong evidence indicates that these events will become more frequent, reducing the ability of coral to recover in between. Long term monitoring by AIMS shows a steady decline in coral cover to its lowest level recorded by 2018 with a slight increase since then.

There is no question that the ultimate cause of this global bleaching is greenhouse gas emissions, amplified by El Nino conditions.  The GBRMPA, which is a Commonwealth Government organisation, is very clear on this, as are the numerous other organisations involved in reef research and monitoring. Coral reefs are very able to recover from catastrophic damage as long as the correct management policies are in place, and in Australia we are fortunate to have many Marine Protected Areas and strong fisheries controls.  The coral cover in this region should still be able to survive longer term, (albeit with reduced diversity) up to a point where the high amount of carbon dioxide in the ocean and atmosphere will eventually result in an algal dominated reef which has much less ecological and economic value.  That would most likely be below, or up to, an atmospheric carbon dioxide concentration of about 500 ppm, projected to occur by about 2050 on our current track.

This global bleaching event must be taken seriously as the strongest possible reminder that we have to reduce fossil fuel use faster, and we have to develop and implement the technology of the clean energy revolution faster.  Good legislation to put the Paris Agreement into effect and create genuine emission reductions is vital.

What’s it like off Port Douglas?

There are two key messages about the effects of coral bleaching here.  Firstly, although a visitor will still have a fantastic experience, because we take you out to the best areas, the reef overall has changed.  In the past it was possible to go out to a random spot and chances are it would have good coral cover, but it was possible to find poor areas.  For the time-being it’s the other way round. Secondly, the effects are very patchy.  The same reef can have both really good areas of coral and areas of extensive mortality as close as just a few hundred metres apart. This is due to a combination of very small scale hydrography and what corals were growing there previously.

What’s the bigger picture?

Reef scientists do a vital role to monitor and report on the reef’s health and they were shocked by the extent of bleaching in 2016-17.  The area northwards from Cooktown was worst affected and is where coral was previously considered the most likely to be resistant to bleaching. There was coral bleaching from the north to south of the GBR in 2020, and the warmest GBR February on record, but temperatures were not high for too long and coral mortality was nothing like 2016/17 (non noticeable in our area).

Evidence from coral growth rings suggests that mass coral bleaching was not normal during at least the last 400 years, with the first record of  global bleaching being 1998, another in 2010 and 2016/17 being the third, and the only instance of back-to-back bleaching years.  Mass bleaching events on the Great Barrier Reef have occurred in 1998, 2002, 2006, 2016/17 and 2020.  The combination of a warming trend and also a strong El Nino seems to have made 2016 the most serious bleaching yet recorded on the reef.  Predictions are that coral bleaching events will become so regular that the reef won’t be able to recover in-between.  Consider that, although the coral animal has been around for millions of years, the Great Barrier Reef as we know it is only 6,000 to 8,000 years old and has been in its current form just since the end of the last ice age, during which time it has experienced stable conditions.

Coral reefs are one of the most vulnerable ecosystems to climate change. Reef scientists are expressing justified frustration at the slowness of collective global policymakers to move to a low carbon economy.  Just in my lifetime atmospheric CO2 has jumped from 320 to over 415 ppm, with vast quantities of extra CO2 dissolving in the ocean.  Separate from warming, on this track, by 2050, ocean acidification will mean all coral reefs worldwide will be eroding and dissolving faster than organisms can build them.

Is this bleaching event important?

On a geological time scale the reef has recovered from major traumas, including major sea level changes in the last 500,000 years with the continental shelf being repeatedly exposed then flooded.  Coral reefs in the past have also recovered and adapted from changes in atmospheric CO2 and sea surface temperature.

The difference today is that the rate of change of atmospheric CO2 is very fast, which creates a problem for organisms to acclimate or adapt. In addition, the reef is affected by human pressures like fishing and agricultural runoff.  These factors are thought to dramatically reduce the ability of the reef to recover from damage.  For example, over-fishing of herbivorous fish will reduce the grazing of algal turf making it harder for new coral larvae to settle.  Excess nutrients from agricultural run-off make it easier for algae to remain dominant on a degraded reef and harder for coral to recolonise.

Studies show that between 1985 and 2012 half the coral cover on the reef was lost, with 48% of the loss due to storms, 42% due to Crown of Thorns starfish outbreaks and 10% due to bleaching.  In the absence of these impacts the estimated recovery in coral coverage would be 2.8% per year. The reef will not disappear but it’s health and diversity over a timescale that affects us and the next generations is on a poor trajectory.  It is sadly a similar, or worse, story on coral reefs worldwide.  It’s not all bad news though, because the potential of reefs to recover shows that good policy decisions can turn things around.

What’s being done?

Overall, reef managers have been aware of the risks of climate change already and have been working to improve the ability of the reef to resist damage, and recover from it. GBRMPA have been working for a considerable time to best manage the fishing on the reef.  A program has been in place for a while to attempt to monitor and control Crown of Thorns starfish numbers.  There is currently a renewed focus (and funding) on improving water quality, particularly in agriculture runoff but also with recent laws to reduce the amount of dredge spoil from ports which can be disposed of at sea.  These things are aimed at making the reef more resilient to climate change. GBRMPA are also very active, along with other scientific and government institutions, in long term monitoring of the reef.  In Queensland we are in a better position for our reefs to recover from bleaching than most other coral reef locations.  Scientists are also now researching possible interventions to help maintain live coral cover in a changing climate.  However, these experimental methods are very expensive and most likely will be viable on small scales, if at all. They also still depend upon climate change being brought under control, which is the major challenge.

What can WE do?

What should we do though on a personal level?  Apart from support the efforts to improve the reef’s resilience, the only thing we really can do is use our buying and voting powers, and what voice we have, to help speed the move to a low carbon economy.  Also, visiting the reef is still a fantastic experience and tourism contributes to the economic case to protect it, as well as making for a better informed public when it’s seen in person.

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