Resets and recovery

There is no doubt that oceanic warming and acidification linked to climate change pose a serious threat to coral reefs, and that substantial losses of living coral have been measured at numerous locations around the tropics in the past five years due to thermal bleaching events. It is the job of scientists like me to convey that information clearly and objectively to the general public.

However, as a coral reef ecologist and expedition guide who has lived and worked throughout the Indo-Pacific for the last 30 years, I find many of the media reports on the reef very frustrating and counterproductive, because gross simplifications such as ‘half the reef is dead’ – a statement which appeared in National Geographic magazine last year – just misrepresent the science and turn people off visiting. Now more than ever we need people to have faith in the credibility of our science, and we need people to see the reef for themselves and become inspired to take the actions necessary to secure its future.

The Great Barrier Reef is an enormously complex reef system that stretches over 2,300 kilometres and contains over 3,000 individual reefs and 900 islands.

It is home to 600 species of corals and over 1,500 species of fish, along with thousands of species of invertebrates and globally significant populations of turtles, dugongs, and cetaceans. Everything we know about the evolution and present ecology of this system suggests that it is constantly in a state of recovery from natural disturbances like tropical cyclones and Crown of Thorns starfish outbreaks, and that any individual reef rarely has the 40 or 50 years needed for the coral community to reach stable equilibrium.

Data from the AIMS long-term monitoring program now stretch back over 30 years, and on reviewing that data, one point is clear – in every one of those 30 years, significant parts of the GBR were losing coral cover due to disturbances, while simultaneously other parts were in recovery and increasing, with the nett change in coral cover over the whole system being the balance of the two.

It is misleading and just plain wrong to say ‘part of the reef is dead’ – some parts of the reef are always in a low coral cover state and this is a natural phase of any given reef in the system, and one that it will immediately start recovering from under normal conditions. Certainly, low coral cover reefs are not what the tourists want to see, and from a scientific point of view if the whole 2,300 kilometres of the GBR moves to a very low coral cover state then it has serious implications for biodiversity – but we are not anywhere near that point yet.

We also need to question whether estimates of living coral cover are the most accurate indication of the ‘health’ of the reef. For example, current research shows that the herbivorous fish assemblage does better on reefs with low coral cover, with substantial increases in numbers and biomass of parrotfish being seen in the northern sector since the bleaching and cyclone disturbances.

Clearly, the location, size and periodicity of the various disturbance events play a crucial role in determining the current condition. Tropical cyclones have been occurring for millions of years and we know Crown of Thorns starfish outbreaks have been affecting parts of the GBR for at least the last few thousand years of this current Holocene Epoch.

Due to elevated nutrients coming off the mainland, there is good evidence that the starfish outbreaks are now occurring twice as often as they were 150 years ago, and with steadily warming seas thermal bleaching events are also taking place more frequently and with more widespread effects, as was evident in the summers of 2016 and 2017. The critical question is not how much of the reef is dead, but how is the reef coping with an increasing frequency of disturbance, and is it still recovering at a reasonable rate?

We have been conducting long-term research into giant clams and photo-monitoring of the reefs at Lizard Island since 2005, and our data set captured the drastic decline in the cover of the delicate branching corals that occurred here after two large cyclones in 2014 and 2015 and then thermal bleaching in 2016.

However this complete reset of the coral community presented us with an incredibly valuable opportunity to study the recovery process, and I’m happy to report that it is proceeding as normal, with our most recent surveys in June 2019 showing hundreds of thousands of juvenile corals blanketing the reef crests around most of the island, along with healthy populations of fish, sharks, turtles and clams, and the sheltered back-reef patches near the resort now looking in excellent condition.

These young corals are growing at an incredible rate, increasing from the size of an olive to an apple in their second year, and from an apple to a watermelon in their third year. This is not just an isolated anomaly, as similar results are being seen in the AIMS surveys and the firsthand observations of the tourist operators and dive vessels that regularly visit the reef.

In summary, yes, parts of the GBR have been affected by a series of disturbances over the last 5 years and, as expected, in those parts of the system where the disturbances were most severe, coral cover is in the lower third of its historical range. However vast numbers of reefs are still in excellent condition.

Even in the hardest hit areas the recovery is well underway, and it is easy to find numerous world-class dive sites along the outer barrier that escaped with hardly any damage at all.

From the perspective of a visiting superyacht, the reef is so big and the number of potential dive sites is so large that you’ll always be able to find some spots in great condition, especially if you have a knowledgeable local guide onboard.

Our marine park system is the best in the world, with about one third of all reefs in no-take reserves, so the numbers of large fish and other marine life are fantastic, and the Queensland coast has a wide variety of other attractions to temp the visitor from waterfalls to rainforests and fascinating indigenous cultural sites. The Great Barrier Reef is still great, and we would like to invite you to come and see it for yourself.

About Dr Andy Lewis

Dr Lewis completed his PhD at James Cook University in the mid-1990s, studying the effects of coral disturbance on populations of fish on the mid-shelf reefs of the central GBR. During this research, he made 225 trips to the reef in his 6-metre power catamaran and completed over 1,000 scuba hours, diving in every month of the year. He then started Reef EcoTours – his own private consultancy firm – designing and delivering coral reef education programmes on the GBR for high school and university students from Australia and abroad.

From 2006 to 2017 he also managed the ecotourism activities aboard the luxury adventure cruise vessel True North, delivering guest experiences across a wide variety of tropical locations from the Kimberley to Indonesia, Raja Ampat, Papua New Guinea and Solomon Islands.

In 2016 he formed the not-for-profit Coral Sea Foundation to further his vision for sustainable coral reef management around the eastern Coral Triangle and Coral Sea arc. The organisation works with indigenous communities in Melanesia, helping them create marine reserves which protect local fisheries and sustain the high-quality dive sites sought after by visiting superyachts and liveaboard dive vessels.

coralseafoundation.net