Jennifer Marohasy

a forum for the discussion of issues concerning the natural environment

Coral challenge

Measuring Old Corals & Coral Reefs (Part 1)

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Fundamental to science is measurement. It is a way of objectively assessing something, anything, even the state of a coral reef, even of an individual coral. Historically coral growth rates were measured by coring the really old massive Porites.

A shutterstock photograph of coring a massive Porites, shutterstock_677259715

Like tree rings in temperate forests, the massive old Porites can be cored to see the banding and from this it is possible to calculate coral calcification rates which are a measure of the growth rate of individual corals.

Peter Ridd has been asking for some quality assurance of so many of the measurements relating to Great Barrier Reef health, including coral growth rates. Key Australian institutions have responded by stonewalling, and in the case of James Cook University, actually sacking him. After two rounds in the federal courts his appeal against his dismissal is finally going to the High Court of Australia, with the next hearing probably in February 2021. While the lawyers are preoccupied with Peter’s rights, or otherwise, to academic freedom and freedom of speech, my concern is whether Peter is actually telling the truth when he says that the Great Barrier Reef is resilient and definitely not dying from coral bleaching, though there is a problem with the integrity of the science.

Most media reports, based on extensive aerial surveys by his one-time colleague Terry Hughes, conclude that the reef is variously 50% or 60% dead from coral bleaching as a direct consequence of global warming.

These media reports do not consider coral growth rates, but rather the area of coral that Professor Hughes has measured to be bleached, with an inference being that this will all die.

Terry Hughes and Peter Ridd can’t both be right.

How can they have come to such different conclusions regarding the health of the Great Barrier Reef? Is the reef really half dead, or not?

Jen/me the other side of a red Gorgonian coral, just two days ago at Pixie Reef.

My working hypothesis is that Terry Hughes’ claims the reef is half dead, are not objective because there is a flaw with his particular survey method. This method is detailed in the technical literature, specifically his paper in Ecology published in 2018 entitled ‘Large-scale bleaching of corals on the Great Barrier Reef’.

Science is not a truth. It is a way of getting to the truth via some method or other that often involves measurement. Sometimes scientists get the method wrong, and so they come up with answers that are also wrong. Sometimes the wrong answer pleases because it is politically correct.

Could it be that in surveying by looking out the window of an aeroplane at such a high altitude (150 metres), and then ground truthing only with respect to a particular reef habitat-type known as the ‘reef crescent’, Professor Hughes has inadvertently recorded a wrong answer? Could he be avoiding, even in denial, when it comes to all the corals in the reef lagoon?

Marine scientists, and anyone with experience diving coral reefs, knows that there are distinct ecological zones at coral reefs. The reef crest, as the name suggests, is the highest part with corals in this habitat often exposed at low tides, sometimes rained-on, and during storms and cyclones this is the part of the reef that will be most likely smashed by big waves. Not surprisingly this habitat/area of a coral reef may be totally devoid of live coral or the coral may be more stunted, and sparse. At the same reef there may be healthy corals in the lagoon and back reef to the leeward side of the crest, and also corals growing down the front slope, even around the perimeter of the crest if it is a flat-topped platform. So, in only surveying the crest, the scientist/Terry Hughes could come away with the impression the reef is dead, when it is actually teeming with life – just not at the reef crest.

Pixie reef from about 100 metres altitude (thanks to my drone Skido). In the foreground (with our boat) is what is known as the reef lagoon. Then there is the reef crest which is mostly showing as beige in colour. Beyond the crest is the front of the reef that slopes more steeply to a greater depth. The types of coral vary so much with these three different habitat types.
A lower altitude picture more clearly showing a delineation between the reef lagoon and reef crest, at the one reef, Pixie Reef not far from the city of Cairns in Far North Queensland.

Professor Hughes specifically states in his 2018 article that underwater surveys were conducted to assess the accuracy of aerial surveys using five 10 x 1m belt transects placed on the reef crest. There is no suggestion that he distinguished between the different reef habitats. He only surveys the reef crest. He surveyed the area that probably had the ‘worst’ and ‘least’ coral.

I tested my hypothesis that Professor Hughes’s methodology is flawed at Pixie Reef just two days ago (25th November). We put my drone Skido into the air and took photographs at 5, 10, 20, 40, 100 and 120 metres of altitude at the reef crest, reef lagoon and reef front slope. Following are photographs just at 5 and 120 metres and just from the crest and lagoon at Pixie Reef. (If I can get a large collection of these type of photographs together from different reefs, they could form the basis of a note for publication about measurement and the importance of measuring different habitat types at the same reef if the idea is to understand the health of the entire reef ecosystem, not just the reef crest.)

A photograph taken at 120 metres altitude of the reef crest is quite different from a photograph of the reef lagoon taken at exactly the same altitude. At 120 metres altitude parts of the reef crest looks rather barren, perhaps bleached. Hughes has mostly concluded that the Great Barrier Reef is 60% bleached from 150 metres looking out a plane window at the reef crest.

The reef crest at Pixie Reef looking down from 120 metres.
The reef lagoon at Pixie Reef looking down from 120 metres. Photograph taken on 25th November with Skido.

The rather large circular boulders in the lagoon photograph from 120 metres up are massive Porites corals. The type of coral that Peter Ridd would like AIMS to core, so we had an objective measure of coral growth rates back 100s of years.

Jen/me laying a tape measure to know that this Porites is about 1.2 metres in height and 1.8 metres wide. These are external measurements. I wonder how old this coral is? It would be possible to know its age through coring (an internal measure), and then by counting the annual growth rings.
This is a close-up of the same Porites showing its golden-coloured tentacles. When the tentacles are retracted, I wonder if the coral is pale pink in colour, rather than golden?

The photograph of the reef crest from 120 metres altitude was taken with the drone (Skido of course) lifted vertically from 5 metres to 120 metres. This is what the same reef looked like at just 5 metres above the crest. There are live corals but no massive Porites or even red Gorgonians, though both exist at Pixie reef but would have been excluded from a 10 metre belt transect across the reef crest and from an aerial survey of the crest, because they exist in a different habitat type.

The reef crest at just 5 metre’s altitude.

A photograph taken at 5 metres from above a section of reef lagoon shows plate corals, presenting as toadstools when photographed from under-the-water, which seems most appropriate given this is Pixie reef. I didn’t find any pixies though.

The reef lagoon at just 5 metres altitude. To really know the corals it is necessary to go under the water, of course.
This is what a plate coral looks like under the water. Of course, at Pixie reef it may look more like a toadstool.

So much thanks to Stuart Ireland for taking me to Pixie Reef, and for taking all the photographs under-the-water, and he also flew Skido. All the photographs (except the shutterstock of the coring), were taken at Pixie reef on 25th November 2020. Pixie reef is just to the north east of Cairns in Far North Queensland.

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The image at the very top of this blog post is of me/Jen swimming over the top of a 7 metre wide Porites at Pixie Reef on 25th November 2020. This is the type and size of coral that Peter Ridd would like to think was still being cored by the Australian Institute of Marine Science (AIMS), as an objective measure of coral growth rates. AIMS used to core these old corals, to get an idea of climate change back hundreds of years. This coral could be more than 400 years old, with annual bands that can be measured at the scale of one year, year on year perhaps back 300 or 400 years to calculate an annual growth rate. So, from the one coral we could (if they cored it) see if growth rates have increased or decreased year on year, or not.

No Data on Coral Growth Rates for 15 Years

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CORALS are animals, closely related to jelly fish, but they differ in having a limestone skeleton. This is hard-stuff, calcium carbonate, and it can persist in the environment and provide an indication of changes in sea level, and also the growth rates of corals, over thousands of years.

Porites corals are typically used to estimate growth rates the Great Barrier Reef. I photographed the surface of this coral when I visited Bramston Reef with Peter Ridd in August 2019. It was so soft, like a carpet, but firm from the corallite: the limestone skeleton supporting individual coral polyps.

There are well established techniques for coring corals, and then measuring growth rates. But as Peter Ridd explains in the following article just published by The Australian, since 2005 there has been no systematic study* of coral growth rates at the Great Barrier Reef.

It is the case that lots of claims are made about declining calcification rates and also declining water quality. But the data is either missing or could actually tell quite a different story.

This is the first in a series of blog posts planned on what Peter is calling ‘The Coral Challenge’. Graham Lloyd has a companion piece, also in today’s The Australian.

Great Barrier Reef Truth May Be Inconvenient, But It Is Out There
By Dr Peter Ridd

We have no data of Great Barrier Reef coral growth rates for the last 15 years. Has growth collapsed as the Australian Institute of Marine Science claims?

Is the Great Barrier Reef (GBR) being affected by climate change, the acidification of the ocean, and the pesticides, sediment and fertiliser from farms? One way to tell is to measure the coral growth rates. Our science institutions claim that coral growth rates collapsed between 1990 and 2005 due to stress from human pollution. Remarkably, despite having data of coral growth rates for the last few centuries, there is no data for the last 15 years. We don’t know how the GBR has fared since 2005.

Corals have yearly growth rings similar to tree rings. By drilling cores from large corals, scientists can measure the growth rates over the life of the coral. The yearly rings are roughly 10 millimetres thick so a coral that is many meters across can be hundreds of years old. In a landmark study, the Australian Institute of Maine Science (AIMS) took cores from over 300 corals on the GBR and concluded that for the last three hundred years, coral growth was stable, but in 1990 there was an unprecedented and dramatic collapse of 15%.

With Thomas Stieglitz and Eduardo da Silva, I reanalysed the AIMS data and, in our opinion, AIMS made two major mistakes. The first was incorrect measurement of the near surface coral growth rings on most of the corals that were giving data from 1990 to 2005. After years of argument AIMS have begrudgingly agreed that they made this mistake. The other problems is that they used much smaller and younger corals for the 1990-2005 data compared with the mostly very large and old corals of the pre 1990 data: they changed their methodology and this is what caused the apparent drop at 1990. When we corrected this problem, the fall in growth rate disappeared.

AIMS continue to dispute this second error and still claim there was a worrying reduction in growth rate between 1990 to 2005. This disputed work is quoted in influential government documents such as the 2019 reef outlook report. I am not cherry-picking a minor problem. It is a fundamental problem with a keystone piece of GBR science.

We thus have a situation that arguably the most important data that tells us about the health of the GBR is highly questionable from 1990 to 2005.

What is far worse is that we have no data whatever since 2005.

The science institutions have not only failed to investigate probable major errors in their work, they have also failed to update measurement of this fundamental parameter while claiming, in increasingly shrill tones, that the GBR is in peril.

But ironically, this failure provides a fantastic opportunity: The Coral Challenge.

For the last 15 years we don’t know what growth rates have been. It is easy to fill in the missing data, and check the previous data, by taking more cores from the reef. AIMS have effectively stated that coral growth is falling at 1% per year. According to the AIMS curve, growth should now be 30% lower than it was in 1990 – a disastrous fall.

I predict it has stayed the same. Either way, it would be nice to know what has actually happened – is the reef really in danger or not?

Peter Ridd is predicating that when the data is finally analysed it will show little change in growth rates, perhaps some improvement. The Australian Institute of Marine Science (AIMS), in contrast, is predicting a significant fall in coral calcification rates.
Science is a method. The best test of competing theories, hypotheses and claims is with the data.

But a second and almost equally valuable outcome of measuring the missing data is that it will be an acid test of the trustworthiness of our major science institutions. AIMS have dug in their heels and denied they made a major methodological mistake. Let’s do the experiment and see if they are right, or untrustworthy. Same for me. If this measurement is done, and done properly, and it shows there has been a major reduction in coral growth rates, I will be the first to accept I was wrong and that there is a disaster happening on the reef.

The coral challenge is a measurement that will have to be done sooner or later. The longer it is neglected the worse it will look to the public. Farmers who are accused of killing the reef are especially interested.

We need to make sure these new measurements are done properly and without any questions about reliability. They must be supervised by a group of scientists that are acceptable to both sides of the agricultural debate on the reef to ensure methodology and execution is impeccable.

End of article by Dr Ridd.
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*There have been some recent studies of calcification rates at a limited number of sites, and these contradict the media headlines and the landmark AIMS study. For example:
‘Long-term growth trends of massive Porites corals across a latitudinal gradient in the Indo-Pacific’ by Tries B. Razak, George Roff, Janice M. Lough, Dudi Prayudi, Neal E. Cantin, Peter J. Mumby in Marine Ecology Progress Series, Volume 626. The Abstract reads:

“Previous studies have reported recent substantial declines in the growth rates of massive Porites corals under warming oceans. However, the majority of these reports are from inshore reefs, and few have explored growth responses in offshore reefs from remote locations with low levels of pollution, sedimentation or nutrient loading. Here, we examined continuous growth records of massive Porites from remote locations spanning a 25° latitudinal gradient in the Indo-Pacific, including Palau, central Sulawesi, West Papua and the central Great Barrier Reef (GBR). Between 1982 and 2012, no significant changes in calcification or extension anomalies were observed at any study location, despite significant increases in sea surface temperature (SST) at all sites. Skeletal density increased linearly by ~0.4% yr−1 in Palau, but no change was found in Sulawesi, yet skeletal density showed a significant nonlinear change in West Papua and the GBR. Skeletal density displayed a significant positive linear relationship with SST at Palau and West Papua, whereas no relationship was observed in Sulawesi. In the GBR, skeletal density exhibited a nonlinear parabolic relationship with SST, with strong negative anomalies occurring following major thermal events. Unlike the ongoing declines in growth rates of inshore corals that have been widely reported, we found that calcification and extension anomalies of the majority of Porites from offshore remote locations do not appear to be exhibiting negative growth responses to warming SST. Our results suggest that reefs experiencing low levels of local stressors may show increased resilience to warming SST in an era of rapidly warming oceans.

Further Reading

There is more background information on Peter Ridd’s work in this area in the book that I edited: ‘Climate Change: The Facts 2017’, specifically the chapter entitled: ‘The Extraordinary Resilience of Great Barrier Reef Corals, And Problems with Policy Science’. Go have a read!

This is a close-up of the corallite walls, of the same coral that features at the very top of this post. It was photographed at Bramston Reef in August 2019. According to Professor Terry Hughes this reef does not exist, at least that is what he told 4,500 delegates at an international conference in Cairns a few years ago. The picture of the mud flat that has apparently replace it was featured on the front page of the Cairns Post. That fake news story was written by News Ltd Journalist Peter Michael.

The coral featured at the top of this blog post is a huge Porites, perhaps 1,000 years old, that the experts claim does not exist because they deny the inshore reefs off-Bowen. I rested on it, while exploring south of Bowen in August 2019 with my paddle board. The black case (the Jarvis Walker) is for my drone Skido, who comes with me paddle boarding.