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

October 30, 2026

The slow disappearance – disease on the reef

What happens after coral disease has run its course? In the fourth article of my six-part photographic series, I revisit colonies I've watched lose living tissue, sometimes alarmingly quickly. From a potentially century-old brain coral that lost most of its living tissue in less than 100 days to the algae-covered skeletons left years later, these photographs reveal the longer-term consequences of coral disease on Norfolk Island's reef.

October 28, 2026

When storms rearrange the reef

Sometimes the sea rearranges a reef in a matter of hours! In the third article of my six-part photographic series, I revisit corals broken, overturned or swept away by powerful swells and storm surges. Some disappeared altogether, while others found surprising ways to survive. Five photographic sequences reveal just how dramatically Norfolk Island's reef can change.

October 26, 2026

When the reef fights back – coral growth and recovery

Not every coral story ends badly! Among six years of underwater photographs are some wonderful examples of growth, survival and recovery. From corals that have grown spectacularly to others that have survived bleaching, breakage or even being turned upside down, this second article in my photographic series celebrates some of the reef's more encouraging stories.

October 24, 2026

The neighbours – six years of watching the same reef

When I began photographing Norfolk Island's reef in 2020, I simply recorded whatever caught my eye. Six years later, those photographs have become a record of individual corals and their changing fortunes – growth, competition, survival and loss. This is the first of six articles looking back at what I've seen, and sometimes what I wish I hadn't.

October 10, 2026

Pulling the rugosity from out of the reef

What do ‘rugosity’, structural complexity and channeling your inner fish have in common? Quite a lot, as it turns out. This week I’m looking at how all the lumps, bumps, branches, holes and ledges on a reef create habitat – with a brief detour into one of my long-standing tricks for navigating tertiary study: write down the jargon until it starts to make sense.

September 27, 2026

How does a sea slug smell?

It started with a close-up of a little Elysia and two rhinophores that looked like tiny rolled-up scrolls. Once I noticed them, I started going back through years of sea-slug photos and realised just how wildly different these sensory organs can be – ridged, rolled, curled, tubular and, in sea hares, distinctly rabbit-eared. So this week’s rabbit hole is all about how sea slugs ‘smell’ underwater, and why their noses come in so many different shapes.

September 19, 2026

The Elite Fleet sails in

Nearly six years ago, my very first blog post was about the strange blue and violet creatures that live at the ocean’s surface – a group I christened Norfolk Island’s ‘Elite Fleet’. Since then I’ve seen plenty of bluebottles and the occasional violet sea snail, but never a by-the-wind sailor. Until this morning. Velella velella is not a true jellyfish, but a colonial hydrozoan with a transparent sail that lets the wind help carry it across the ocean. So what exactly is this extraordinary little creature, how does it ‘sail’, and what connects it to the rest of the fleet?

September 18, 2026

In a nutshell – where I stand on the proposed Norfolk Island Marine Park

I support the proposed expansion of Norfolk Marine Park and its renaming as Norfolk Island Marine Park. There is much to welcome – strong offshore protection, no mining, and recognition of the importance of sustainable local fishing. But I also have some reservations. Why does Cascade need to be removed from the Marine Park at all? How will more than 430,000 km² actually be monitored and enforced? How do we make sure Norfolk people have a genuine role in management? And, above all, how do we ensure that the enormous new park does not draw attention away from the small, stressed reef immediately beside us?

September 13, 2026

No seagrass, but plenty of turtles

Norfolk Island does not have seagrass, although one of our most conspicuous green algae is often mistaken for it. Feather and grape Caulerpa can both form striking patches across the lagoon. I take a closer look at what Caulerpa actually is, why it is so easily confused with seagrass, and where our green turtles fit into the story.

September 6, 2026

Watching El Niño from Norfolk Island

El Niño is strengthening across the Pacific, but that does not tell us exactly what the coming months will bring to Norfolk Island. After a long wet spell, I am watching our rainfall and water supplies more closely again – and, underwater, keeping an eye on sea temperature, algae, coral recruits and the fish that turn up on the reef.