Coral spawning, Norfolk Island 2021 — Norfolk Island's Reef

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.

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Out on a swim in the lagoons on Norfolk Island on the morning of 27 December 2021, the mood was palpably different.

Call me fanciful, but I immediately noticed a frisson of excitement among the fish. Lots of activity and agitation. And all kinds of slightly unusual observations:

A fish over here, who always, but always, is found over there (many fish have very small home ranges and are quite territorial); the little scissortail sergeants (Abudefduf sexfasciatus) bobbing up to the surface more than normal, and taking big gulps; and the multispine damselfish (Neoglyphidodon polyacanthus) going bonkers over a couple of different corals.

So I do what I normally do – take photos, then go home and start trying to find answers to my questions.

I didn’t have to do much digging though. As I was driving home from my swim, my phone pinged a few times. Jim Castles the Australian Marine Parks manager on-island had messaged me with photos showing a slick of coral spawn floating in Ball Bay, a semi-circular bay formed from a volcanic imploding caldera on the south-east of the island. See the images and video, below.

A pink tide, Ball Bay

‘But this wasn’t supposed to happen until January!’ we both said!

Clearly nature had other ideas.

And for those who are wondering, remote Norfolk Island, just 5 km by 8 km in size, and about 1,600 km from the east coast of Australia and 900 km from Lord Howe Island, its nearest coral neighbour, is the second most southerly coral reef in the world. Consequently, our annual coral spawning takes place a month or more later than the Great Barrier Reef Marine Park. On Norfolk Island, the coral spawning event normally occurs eight to ten days after the full moon in January. Full moon will be on 17 January. But perhaps the full moon in January 2022 maybe a bit too late in the season, so December, it seems, it is!

At that point, I didn’t think Emily and Slaughter Bays had spawned, but the coral looked very ready. They take on a slightly fuzzy appearance as spawning time gets closer. The hammer corals (Fimbriaphyllia ancora), in particular, were looking rather fecund that morning, although most didn’t have the tell-tale pink in their tentacles. But one did! And the multispine damselfish thought that this was a very choice treat, as you can see in the image, below.

A hammer coral colony being grazed by multispine damselfish

A scissortail sergeant grazing on coral spawn that has come into the lagoon

Similarly, the scissortail sergeants were finding something on the surface worth eating as well.

So, although coral spawning had occurred outside the lagoons, and certainly at Ball Bay and Cascade, it looked like we are in for a coral spawning on the night of 27 December inside the lagoons.

Pink coral spawn floating on the surface of Emily Bay, Norfolk Island, 28 December 2021

And as predicted, when I went out for my swim on the morning of 28 December, this was the view from under the water.

Things weren’t quite as frantic in the lagoon on the morning of the 28th. I think all the full bellys had calmed things down, although there was still plenty of activity.

For example, normally our little butterflyfish get around in twos and sometimes threes. Occasionally you will see a few more together. I came around a corner of the reef to be greeted by a loose gathering of lots of butterflyfish all enjoying the coral spawn, which you can just make out floating in the water. My photo, bottom, really doesn't do the scene justice. There were lots of fish!

In my photo there are: bluespot butterflyfish - Chaetodon plebeius; blackback butterflyfish - Chaetodon melannotus; black butterflyfish - Chaetodon flavirostris; and the most numerous, threadfin butterflyfish - Chaetodon auriga. I’ve included their photos, bottom images.

Australian Marine Parks has placed larval settlement plates in six locations around Emily and Slaughter Bays, Norfolk Island.

Australian Marine Parks has placed larval settlement plates in six locations around Emily and Slaughter Bays. These plates have been curing for a few months in the saltwater near the Kingston Pier, but now they have been deployed.

These plates will give Parks Australia and researchers valuable information about the success of the coral spawning event. As the coral spawn disperses and settles in the lagoon, some of it will fall onto the plates. These will be collected and examined to determine diversity and density of coral larvae.

If you see them, please look, but don't touch. We need this valuable information.

An unusual loose gathering of butterflyfish in Emily Bay, Norfolk Island. The water column is full of pink coral spawn.

Bluespot butterflyfish

Blackback butterflyfish

Black butterflyfish

Threadfin butterflyfish

August 1, 2026

Reflections of an accidental marine scientist

What I thought would be a steady plod towards retirement, with plenty of time spent nursing grandchildren, was abruptly upended exactly six years ago today. This is the story of how an environmental catastrophe changed the course of my life – and led me to reinvent myself. It is a reflection on how, and why, I became an accidental marine scientist.

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.

July 13, 2026

Reef reality in pictures

Let the pictures do the talking. This is the reality on Norfolk Island’s reef today, laid out in a two-minute video.

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.