The spatiotemporal dynamics of a coral disease
White syndrome on a Hynophora pilosa colony, Norfolk Island, 23 November 2023
The spatiotemporal dynamics of a coral disease, or, a pictorial study of the spread of white syndrome, over time, in a Hynophora pilosa colony on Norfolk Island.
This beautiful coral colony is in the middle of the channel that runs between the contiguous Emily and Slaughter Bays, in Norfolk Island’s inshore coral reef lagoon. It’s one of my favourite places to pause and admire the scenery, when I’m out on my swim.
On 23 November 2023, I spotted a new outbreak of white syndrome. Since then, I’ve been following its rapid growth as it has spread across the Hynophora pilosa colony. To see the white syndrome aggressively overtake this coral colony in such a short time is heartbreaking.
As the disease has spread outwards, I’ve noticed fish, mainly multispine damselfish (Neoglyphidodon polyacanthus) and banded scalyfins (Parma polylepis), nibbling on the dying coral polyps (see images, bottom).
Algae growing on the dead white skeleton of the coral colony, 18 December 2023
Keen-eyed readers will notice the colour change in the disease as time goes on. When it starts, the dead coral tissue is a stark white, because all that is left is the coral skeleton. The polyp and its zooxanthellae (the algae that lives inside it and gives it is colour; for more information click here) are dead and gone. I have had some people tell me, mistakenly, that the coral has bleached and that it should recover; when it does it will look the same colour again. Sadly, there is no recovery from white syndrome. The change in colour is caused by opportunistic algae growing on the dead skeleton, turning it green or brown. On the right is a close up of the dead coral photographed on 18 December. It is easy to see the green alage.
I will keep updating this blog post in the coming weeks, but as of 18 December 2023, I am hoping the disease has run its course and the remainder of the massive coral will survive, albeit in a weakened state.
If any coral health researchers would like the high-resolution images to study the speed of spread, email me via the contact details on this website.
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More than 38% of two major coral types (Montipora and Acropora) exhibit signs of disease in both Emily and Slaughter Bay. These disease rates are significantly higher than other coral reefs where disease rates generally do not exceed 5%, and in some cases are significantly lower.
Significantly, disease rates in Slaughter Bay have increased from 0% in April 2021 to 42% in September 2022.
Ammonium and nitrate/nitrite levels were up to 5 times higher than the default ANZECC guidelines for offshore marine ecosystems in Emily Bay and Slaughter Bay during a rainfall event when the Emily Bay creek was open in April 2022.
Fluorescent Whitening Compounds (FWCs) are optical brighteners found in laundry detergents and toothpaste. Water courses in the Emily and Slaughter Bay catchment (and adjacent catchments) were surveyed for the presence of these compounds. FWCs were identified throughout the Emily and Slaughter Bay catchments and at the freshwater outlet into Emily Bay, indicating continued grey water input into the catchment.
Additional background information about the state of Norfolk Island’s reef can be found in various blog posts, here: