The Great Barrier Reef observed over five years

Anjani Ganase, marine biologist, returns to the Great Barrier Reef in Australia. In this feature, she warns that we ignore climate change to our peril.

In about week’s time, I’ll be heading out by boat on my final expedition to survey the Great Barrier Reef (GBR) before I return to the Caribbean. This will be the fourth time exploring the GBR, since I first came to Australia five years ago.

The GBR was my first home in Australia. I lived on a research station on tiny Heron Island, located in the southern GBR. I lived on Heron Island for about six months, working on experiments to see the effect of extreme temperatures on corals. During this time, I explored the reefs, viewed migrating whales and followed nesting and hatching turtles on the beach, where the GBR is also their home.

After Heron, I got the dream job as part of a research expedition, surveying the rest of the Great Barrier Reef. Over the next four months my home became a boat and my office the largest coral reef ecosystem in the world. 2300 km in length covering an area of about 344,400 km2, the GBR sits just within the tropical latitudes along the northeastern tip of Australia. In 2012, our team made the amazing effort to survey and map about 1000 km2 of reefs over four months, still less than 1 % of its total area. The first time I explored these reefs in 2012, many sections of reefs seemed almost picture perfect - vibrant and colourful coral cities bustling with fish and marine life. As we steamed north to more remote locations, it appeared as if these healthy sections of reef became more extensive, away from coastal development, ports and agricultural lands. Some reefs are so faraway that sharks and fish approach divers with a curiosity as if they have never engaged with a human and are unafraid of being fished.
Healthy hard coral in the far northern Great Barrier Reef, 2010. Photo by The Ocean Agency / XL Catlin Seaview Survey.

Although the expedition in 2012 was my baseline for observing change on the Great Barrier Reef, the GBR has been home to great scientific research for generations and has been monitored broadly for coral reef health since the 1980s. A compilation of these assessments, released in 2012 while we were doing our own survey, stated that there was a 50 % loss in hard coral cover on the shallow reefs (6 – 9 m depth) of the Great Barrier Reef over the last 27 years (De’ath et al. 2012). Most of this loss was a result of Crown of Thorns outbreak, potentially linked to increased water nutrient pollution (runoff from agriculture), cyclone damage and coral bleaching (De’ath et al. 2012). It was also noted that this decline was not evenly distributed across the GBR; the central and southern regions of the GBR declined significantly more than the northern section, which had a relatively stable hard coral cover over the years (De’ath et al 2012). This statistic overlapped with much of our observations, where the healthiest reefs with the highest coral cover were indeed more common on remote far north GBR reefs. It was necessary for me to adjust my first view observations and judgements, so that I can imagine what these impacted reefs may have looked like 27 years ago.

I was able to visit the GBR two more times since 2012, but most of the subsequent visits followed major disturbance events. In 2014, we specifically visited outer reef sites just off Lizard Island, which were in the direct path of Cyclone Ita, to assess the immediate damage of the surrounding reefs. One week after the cyclone, we witnessed parts of the Ribbon Reef not just stripped of coral but with infrastructure completely turned over; and parts where the framework had avalanched on to deeper parts of the reef. Also apparent was the absence of the usual marine chatter that typically inhabited the living corals.

At the end of 2014, we resurveyed many of our original our surveys from 2012 to assess how reefs changed from two year before. It was clear the impacts that Cyclone Ita had affected, not only in the sections of the reef directly in its path, but reefs much farther away. Within this short time, I was already witnessing significant degradation to reefs I had been introduced to, only two years ago.

In 2016, sections of the GBR again suffered from a different natural disaster, this time it was one of the longest and most severe coral bleaching ever recorded. Overall, higher than average water temperatures resulted in the bleaching being up to four times more severe compared to 1998 bleaching (Hughes et al. 2017). The bleaching event extended to more offshore reefs and the northern sections of the GBR with the southern section being saved by the winds of tropical Cyclone Winston that stirred up the water column. Surveys carried out on the GBR in the months following bleaching found that the heat stress alone was so severe that it was the main prevailing factor for bleaching and death of the corals, even across reefs of varying anthropogenic stress, protection and bleaching history (Hughes et al 2017).  This time, it was clear that climate change driven coral bleaching was the culprit.
Documenting the dead coral overgrown by cyanobacteria after the bleaching event at Lizard Island on the Great Barrier Reef in May 2016. Photo by The Ocean Agency / XL Catlin Seaview Survey.

Considering that many corals may take several decades to recover depending on the species; and there is a predicted increase in temperature anomalies and bleaching events under future scenarios of climate change, the decline in coral cover will likely continue, and even increase in its rate of decline. Local management may not be able to significantly improve the recovery of coral reefs, without active reduction in our carbon dioxide emissions and global warming.

As we survey GBR over the next two weeks, we hope to reveal the cumulative effects of these disturbances over the last five years and taking into account the historical disturbances. We may be able to identify why some reefs continue to prevail while other communities lose following one or other, or multiple, disturbance. I suspect that many of the once pristine reefs that I have observed might be unrecognisable and in a state that is unlikely to recover in my lifetime. It also makes me think about my mentors and their mentors who have been observing changes in the reefs for much longer, over forty years, and I cannot fathom how many reefs that they have witnessed degrade over the years. However I’m also comforted that these experiences only make their drive to present their work to change the minds of citizens, influencing policies and laws, only stronger. I hope that I would be able to do the same, because to resign means to fail our future generations.

De’ath, Glenn, et al. "The 27–year decline of coral cover on the Great Barrier Reef and its causes." Proceedings of the National Academy of Sciences 109.44 (2012): 17995-17999.

Hughes, Terry P., et al. "Global warming and recurrent mass bleaching of corals." Nature 543.7645 (2017): 373-377.

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