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.
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.
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.
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 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.
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’.
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.
So much thanks to Adrenalin Snorkel and Dive for a great day at the reef.
You can read more about the structure and history of coral reefs in this central region of the Great Barrier Reef at a previous blog post, about Britomart Reef by clicking here.