Archives for March 2021

Coral reefs are the most extraordinary places, and they are essentially layer upon layer of death. Topped with the most extraordinary diversity of life forms.

Consider Britomart Reef, for example, it is a mid-shelf coral reef 120 kms north of Townsville in the central Great Barrier Reef. The modern reef started to grow about 9000 years ago on a mound of limestone. Limestone is a sedimentary rock composed of calcium carbonate that was the skeleton of coral polyps. Dead coral is not limestone, it has to first undergo cementation.

The limestone at the very bottom of Britomart Reef would have been laid down around 125,000 years ago by hard corals when sea levels were a little higher than they are now.

Then this coral reef went extinct, as sea levels fell more than 120 metres. During the depth of the last ice age (16000 years ago) Britomart Reef would have been a ridge of limestone within a Eucalyptus woodland with the ocean about 64 kilometres further to the east.

Then the ice caps melted sea level rose, and eventually corals started to grow from the dead limestone. The corals hadn’t survived at Britomart, rather the corals recolonised at the beginning of the current geological epoch known as the Holocene.

The modern reef at Britomart is 25 metres thick, with most of this ‘reef mass’ accumulated between 8500 and 5000 years before present on top of the existing platform of limestone. So, the live coral at Britomart is but a thin veneer growing on top of 25 metres of dead coral – on top of the platform of limestone that dates to the Pleistocene.

We know this from coring – holes drilled through this reef back in the 1980s, analysed and radiocarbon dated. According to the paper by David Johnson, Christopher Cuff and Eugene Rhodes published in Sedimentology (volume 31, pages 515 to 529) the top 5 metres at Britomart Reef is classified as ‘fragmented coral boundstone’ that is ‘disoriented, abraded and bored, coral gravel up to 6cm across, which is encrusted and bound by coralline algae.’

That paper was published back in 1984. I dove at Britomart last November and while it was the prettiest of reefs, there were so many dead plate corals. I’m guessing these corals bleached over the last few summers and are now in various stages of decay.

The feature image (photograph at the very top of this blog post) shows a dead, and algal infested plate coral in the foreground. Can you see it? The second image (photograph below) shows dead plate corals as the ridge drops away. In the third image there are two very large dead plate coral to the left, and another towards the bottom of the drop-off. In the fourth picture I’m holding on to a more recently dead plate, now covered in algae.

I’m posting these pictures to show what recently dead plate corals looks like, and to explain that the dead coral extends down 25 metres and represents continuous cycles of death and regrowth over the last 9000 years. This is to inform some discuss about corals at another reef, Pixie Reef. I’ve not been able to find any technical papers about Pixie, but I have started some discussion about Pixie at my Facebook page here https://www.facebook.com/JenniferMarohasyOfficialPage .

We are just starting to discuss the transects photographs in Table 1.1. (specifically the first and second photographs in the first transect) that include patches of what I am fairly sure are dead plate coral.

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Further reading:

David Johnson et al. 1984. Holocene reef sequences and geochemistry, Britomart Reef, central Great Barrier Reef. Sedimentology, 31, 515 – 529.

The photographs were all extracted from video filmed by Stuart Ireland, and one day it will be turned into a documentary.

I wasn’t the one who took that bite out of that green plate coral. Can you see what looks like a bite mark? It is at about 4 o’clock on the large, green, plate coral, which is also one of the transect photographs taken last week, on 22nd February at Pixie Reef by Leonard Lim.

I’m so proud of the 360 underwater photographs taken along 36 transects that were laid in four different habitat types: at the reef front, in the back lagoon, at the reef crest, and we also laid three transects at the bottom of the reef crest – beginning at a depth of ten metres at what I’m calling the western flank. It was hard work, over two days, but these photographs and the corresponding videos will provide some evidence as to the state of the corals at Pixie reef for that moment in time.

Table 1.1

Date: 22 Feb 2021
Habitat: Crest
Starting locations:
  Rep1: (16°32.717'S, 145°51.672'E), Rep 2: (16°32.711'S, 145°51.668'E),
  Rep3: (16°32.710'S, 145°51.663'E)

Depth	Rep	@1m	@2m	@3m	@4m	@5m	@6m	@7m	@8m	@9m	@10m
2	1
2	2
2	3

I was so grateful that we were able to lay transects along the reef front at Pixie. If you click on the thumbnails in the above table you will see some of the photographs. There will be many more uploaded at the ‘Pixie Reef Data Page 2021’ over the next couple of weeks. Leo took 120 photographs from the reef front at two different depths: 3 metres and also 6 metres.

Last November, I only visited the back lagoon. More usually, the prevailing wind is blowing onto the reef from the south east/from the front making access to this front section of the reef difficult. But on 22nd February the wind was blowing from the north northwest. (It was a hot day, and we did return to harbour under Anvil clouds, with Stuart bringing his little speed boat with us safely through a storm that afternoon. Thank you.)

This reef, Pixie Reef, was ‘surveyed’ back on 22nd March 2016 from the air by Terry Hughes of James Cook University during one of his fly pasts. It was concluded from that single observation/glance-down from 150 metres altitude that that this reef was 65% bleached. The inshore reefs north of Cairns were more or less all written-off, back then, by the experts and the mainstream media, as ruin – as dead. But they are not, not at all. (And I do worry for all the children who now believe this precious environment/the Great Barrier Reef is dead from ‘carbon dioxide pollution’.)

Pixie Reef was one of thousands of coral reefs ‘surveyed’ during March to April 2016, with the overall conclusion – reported on the front-pages of newspapers worldwide and now incorporated into schoolbooks – being that the Great Barrier Reef is more than half dead: that more than half of the corals have suddenly died from global warming.

It is my hypothesis that these coral health assessments of the Great Barrier Reef, comprising 1,156 reefs including Pixie Reef as published in the peer-reviewed technical literature by Terry Hughes and others, are yet another example of the mismatch between official government-sponsored (taxpayer funded) propaganda masquerading as science, versus reality.

It is only under the water that we can see the true state of the corals.

Of course, Pixie Reef is where I found and named that extraordinary, large and old Porites after Craig Kelly MP. I visited ‘Porites Craig’ again on 22nd February. That bolder coral still looks relatively pale from a distance, but up close it is evident that the massive coral colony/Porites Craig has a lot of colour – with all its corallites intact and healthy.

There is such a diversity of different coral types, coral species and in so many different coral colours at Pixie Reef.

And what about that green plate coral – with the bite mark? (Could it be from the pixies?)

I hypothesis that the little beige-coloured brain coral, which you can see directly under what I am describing as the bite mark, is responsible. This is perhaps a species of FavitesSymphyllia, and it could be extending its tentacles at night and eating up that section of plate coral directly above it. Very likely the Symphyllia sp.Favites sp. is eating away at the Acropora sp., so it has access to sunlight for its own zooxanthellae.

There are so many of them at Pixie Reef – all different types of corals including healthy plate corals in shades of green and also brown. You can see them in the transect photographs, click across to the new page where they will be uploaded over the next couple of weeks: https://jennifermarohasy.com.dev.internet-thinking.com.au/coralreefs/pixie2021/ .

Postscript

This is Part 4 of ‘Measuring Old Corals & Coral Reefs’, essentially written to let everyone know about the new data page for Pixie Reef. You can access other data pages here: https://jennifermarohasy.com.dev.internet-thinking.com.au/coralreefs/

There has already been a Part 1 and a Part 2:
https://jennifermarohasy.com.dev.internet-thinking.com.au/2020/11/measuring-old-corals-coral-reefs-part-1/
https://jennifermarohasy.com.dev.internet-thinking.com.au/2021/01/measuring-old-corals-coral-reefs-part-2/

The blog post about the garden of old Porites at Myrmidon should really be Part 3, ‘tis here: https://jennifermarohasy.com.dev.internet-thinking.com.au/2020/12/gardens-of-old-porites-without-sharks/

And so much thanks to Leonard Lim and Stuart Ireland for all the photographs and video from Pixie last week, and to The B. Macfie Family Foundation for believing in us.