How Brown the Corals – That were Pink Last Year

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The colours on the Coral Health Chart are based on the actual colours of bleached and healthy corals. Each colour square corresponds to the concentration of symbiotic algae living in the coral tissue, which is directly linked to coral health.

From Jennifer Marohasy

October 12, 2023 By jennifer

I was back at John Brewer Reef last week and many of the corals are now dark brown. John Brewer reef has lost its pink, for the moment.

The corals in this section of John Brewer Reef are now very brown, or green, because they are replete with zooxanthellae.

There is a Coral Watch program that was developed at Heron Island by the University of Queensland. The ‘Coral Watch Coral Health Chart’ quantifies the health of a coral according to the intensity of its colour that is considered a proxy for the concentration of zooxanthellae. A report on the status of corals at Heron Island indicates that the corals tend to score between 3 and 4, which is considered healthy.

Dive Master Paul Crocombie holds a Coral Health Chart against a branching *Acropora* at John Brewer Reef last Tuesday, 3rd October 2023.

According to The Coral Watch website, to score a reef:
1. Choose a random coral and select the lightest area.
[Don’t include the growing tip that is usually white.]
2. Rotate the chart to find the closest colour match.

Photographed at John Brewer Reef last Tuesday by Leonard Lim, colour chart held by Paul Crocombe.

3. Record the colour code on a data slate.
4. Select the darkest area of the coral and record the matching colour code.
5. Record the coral type.
6. Continue your survey with other corals. Record at least 20 corals.
7. Submit your data online at http://www.coralwatch.org

Ideally this is done with the chart beside the coral at the reef. But, given the extraordinary quality of the underwater photographs taken by Leonard Lim last Tuesday, and that some include the colour chart held by Paul Crocombe, a Dive Master, Skipper and Owner of Adrenalin Snorkel and Dive, I am attempting some interpretation here, so we might be able to quantify how brown the corals were last week for that patch of reef.

All four colours of the symbiotic algae/zooxanthellae in the Coral Watch Coral Health Chart are shown in this photograph. I calculate the average colour to be 3.7, I would have guessed that it was even higher.

Photograph taken at John Brewer Reef on Tuesday 3rd October 2023 by Leonard Lim.

I can’t bring myself to write on this photograph, it is so beautiful. Another from John Brewer Reef on 3rd October 2023.

This section of reef, towards the north east, has particularly healthy corals and exceptional coral cover. There are some sections of John Brewer reef that are all coral rubble. Coral cover and coral colour varies with the particular habitat. Different habitats include reef crest, reef front and back lagoon.

I first visited John Brewer reef on 10th April last year, with photographer Leonard Lim and cinematographer Stuart Ireland, specifically to photograph and film the bleaching. At the time this reef, John Brewer Reef, was reportedly the centre of a sixth mass coral bleaching – and I wanted it all recorded, for that moment in time.

We did find some corals that had bleached white, but mostly I was surprised at how pink the reef was back then. Leonard took some exquisite photographs and Stuart filmed sections of coral that can be viewed in part 1 of a documentary entitled ‘Bleached Colourful’.

The same section of reef, but quite a different colour in April 2022.

Back in April 2022, many of the corals had ‘kicked out’ their symbiotic algae and so it was possible to see more of their natural pink colour. The pink is from a florescent protein that can ‘upregulated’ when corals are stressed.

It is somewhat counter intuitive that the more symbiotic algae, also known as zooxanthellae, the healthier a coral and the less colourful!

According to the Coral Watch Website:

“The Coral Health Charts are based on the actual colours of bleached and healthy corals. Each colour square corresponds to a concentration of symbionts contained in the coral tissue. The concentration of symbionts is directly linked to the health of the coral. All you have to do is match the colour of the coral with one of the colours on the chart. You then record the lightest and darkest colour codes, along with coral type, on a waterproof data slate.

The hues on the chart represent the most common colours of corals, and help our eyes to make an accurate match. The brightness of the colours ranging from 1 to 6 are the same on every side of the chart, so you can mix and match sides.