Combine bacteria, fungi, and maybe a sponge = one toxic mess

Out on A Swim

‘Out on a swim’ is a coral reef blog that tells the stories of the characters who live under the waves and what has caught my eye when ‘out on a swim’ in the lagoons of Norfolk Island. It is also a record of the difficulties Norfolk Island’s reef faces, like many others around the world, as a result of the poor water quality that has been allowed to flow onto it.

This page shows the most recent blog posts. For the complete catalogue, visit the ‘Out on a swim index’ page.

This blog is rated in the Top 20 Coral Reef Blogs in the world.

I want this blog to be a record of all that is happening in our bays – the things that are worthy of celebration, and the things that are not so palatable and are hard to see.

Today’s post is one of the latter. Over the last six weeks, I have increasingly noticed a disease that is presenting differently to the white syndrome that we have sadly become used to seeing, and which I have described in this blog several times. With white syndrome, the coral tissue dies and the white skeleton of the dead coral remains, eventually getting overgrown by surface algae. With this disease, which I have seen before but not to this extent, the coral goes grey-ish black and sometimes looks like it is almost dissolving or melting away.

I sent some photos to Associate Professor Tracy Ainsworth, and her colleagues, Associate Professor Bill Leggat and postdoctoral fellow Charlotte Page, our coral health researchers contracted by Australian Marine Parks to monitor the reef’s health.

Old Gnarly’s hole on 20 January 2024. You can read more about him here: Old Gnarly, the swal doodle

This morning, Tracy got back to me, and it wasn’t pretty:

‘I would say this is the advanced stage of the Monitora[1] disease we have been seeing across the bays the last few years. This is a very similar disease progression to the Atramentous Necrosis first described on the reefs adjacent to Magnetic Island; the Monitipora disease over the past few years in Norfolk’s bays displays very similar progression patterns.’[2]

Tracy goes on to explain that in diseases where the skeleton is black like this, there is a microbial black matt growing inside the coral skeleton. This tends to expand inside the skeleton, below the tissue. Generally, black matts are a mix of a (sulphur oxidising) bacteria, fungi, and in some instances a black boring sponge that is also very dense with bacteria and sulphur oxidising bacteria. This creates a toxic environment that kills off the coral tissue, causing it to die and slough off.

Tracy says, ‘It’s possible the temperature and nutrient conditions are allowing these stages of colonisation/growth/necrosis to run very quickly.’

If you wish to know more about coral disease in Norfolk Island’s lagoons, I suggest some useful reading is Page et al.’s paper (link, below).

All the photographs in the gallery, below, were taken in January 2024 and are recent outcrops of the disease.

[1] Montipora is a genus of coral, consisting of at least 85 known species.

[2] Page, C, Leggat, W, Egan, S & Ainsworth, T 2023, A coral disease outbreak highlights vulnerability of remote high-latitude lagoons to global and local stressors, iScience, vol. 26, iss. 3, viewed 29 January 2024, https://doi.org/10.1016/j.isci.2023.106205

July 24, 2026

From ridge to reef: unpicking the Waterway and Wetland Strategy

Norfolk Island’s draft Waterway and Wetland Strategy will guide work for the next ten years. I support its intent, but it needs to be clear, practical and measurable – joining the dots from ridge to reef so we know whether public money is improving water quality and helping the reef.

June 28, 2026

The red seaweed behind low-methane beef

A small red seaweed on Norfolk’s reef has become part of a much bigger story. Asparagopsis taxiformis can look like a delicate red feather duster or, at another stage of its life cycle, like a tiny cottony pom-pom. It is beautiful, easily overlooked, and now being used in the cattle industry to help reduce methane emissions. This post looks at the reef oddity behind the low-methane beef story – and why repeated local observation can be more useful than it first appears.

June 20, 2026

From coral scar to aatuti farm

Aatuti are bold little algae farmers, but how does one of their farms begin? Over the past year, I have been following several coral patches as small white scars became algal footholds, then larger defended patches. I still cannot say what caused the first wounds, but the photo sequences show something fascinating: on a reef where algae is already gaining ground, even tiny changes on the coral surface can become part of a much bigger story.

June 15, 2026

Norfolk’s water quality – when action is reported as outcome

A recent Australian Government media release presents investment, monitoring and catchment works as progress on Norfolk Island’s water quality. Some of that work is useful, and some of it was badly needed. But activity is not the same as proven improvement. This post looks at Kingston sewerage, wetlands, cattle, acid sulfate soils, groundwater and reef health, and asks whether Emily Bay and Slaughter Bay are actually being better protected.

June 14, 2026

How surgeonfishes got their name

Surgeonfish are named for the sharp little scalpels near their tails, but on Norfolk’s reef their more useful work happens at the other end. Pencil surgeonfish, bluespine unicornfish and their relatives help browse algae across the reef – a small daily job that becomes very valuable on an algae-rich lagoon reef like ours.

May 28, 2026

A shrimp storm

While setting my research cams last week, I swam into what looked like an underwater snowstorm. It appeared to be the aftermath of a mass moulting event, with large numbers of tiny, translucent shrimp-like exoskeletons drifting together near the surface.

Kingston dredging: what happens when a reef does not fit the framework

This correspondence with DCCEEW is about more than one dredging proposal. It is about what happens when an ecologically distinctive place is assessed through standard tools that do not always make its most important values easy to see. I am publishing it here because that is something we need to be aware of, both on Norfolk Island and more broadly in Australia.

May 24, 2026

Kingston dredging: the project advances, the questions remain

Kingston dredging is edging closer, and the paper trail is growing. This post brings together earlier correspondence with the Department and the latest media release so readers can see what has been asked, what has been answered, and what still remains unclear about the project, its rationale, and the protections proposed for the reef.

May 17, 2026

The lime-green coral in Slaughter Bay – a 40-year paper trail

Green Mountain – the name I give this coral in my database – is a coral I’ve photographed for years as I swim past. Then I found its backstory in the Norfolk Island National Parks archives: a rough map, reused paper, a note in the margin – ‘still thriving’. That’s how baselines begin.