The smiling notch-head marblefish — 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.

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

Native to the South Pacific and the tropical areas of the Indo-Pacific region, feather Caulerpa, Caulerpa taxifolia, looks like a gorgeous, lush, green meadow. And at the moment we seem to have large expanses of it in our lagoons.

In its native habitat, like Hawaii for example, it has shown no invasive tendencies. However, when out of its natural habitat range, in areas of New South Wales, or over in California for example, it is regarded as a marine pest, mainly because it is hardy and fast growing and can be detrimental to other marine life.

Victoria, South Australia, New South Wales and New Zealand all regard it as a pest species. And, unfortunately, fish don’t like to eat it.

It is popular for use in aquariums as a decorative plant, although it has been banned from sale in New South Wales. Just the tiniest piece escaping into the wild can settle and grow out of control rapidly, growing as much as 2.5 cm a day.

To be honest, I’m not sure what to make of our current carpet of feathery fronds, but I do know it is regarded as occuring naturally here. Meanwhile, I am sure fellow snorkellers will concur, we have lots of it!

On a cheerier note, I’ve noticed many species of fish turning up their colours. Last week, I saw a mature male sergeant major. Normally black and white stripes, with its yellow epaulettes, this Indo-Pacific sergeant, also known as a sergeant major, Abudefduf vaigiensis, was a beautiful blue and green hue, still with the yellow shading and black stripes.

I spotted my little Blacktip morwong, Cheilodactylus francisi, away from the safety of his regular stomping ground on the reef, out in Emily Bay. It has been almost a month since we last crossed paths, so it was great to see him again.

And were the Norfolk cardinalfish, Ostorhinchus norfolcensis, beginning to pair off? I’m not sure, but it certainly looked like it! You can read more about their breeding habits in an earlier blog post, here: The mouth-brooding Norfolk cardinalfish.

I can’t close this week’s nature blog off without saluting the gorgeous notch-head marblefish, Aplodactylus etheridgii, that let me take his photo from right up close. To me, the most fascinating thing about this image, apart from the unusual angle, is his eyeball, so clear you can see right through it (bottom image, below). Amazing!

A pair of Norfolk cardinalfish

Blacktip morwong

Indo-Pacific sergeant, adult male

Indo-Pacific sergeant

August 25, 2026

When the map changes

A fish once thought to belong only to Norfolk turns up elsewhere; another appears here hundreds of kilometres beyond its known range. Cardinalfishes and a Sabre squirrelfish show how our maps of species distributions are revised.

August 24, 2026

Endemic, native, undescribed – what do these words actually mean?

A Norfolk chromis that turned out not to be Chromis fumea, a blenny found nowhere else, and a tiny goby that may not yet have a name. A look at what we mean by native, endemic, undescribed and newly described – and why scientific names sometimes change.

August 16, 2026

What’s grazing in the green stuff?

A proliferation of Bryopsis on the reef has brought some beautiful little underwater grazers with it. I follow the trail from sap-sucking sea slugs and egg masses to a bigger question – why is there so much Bryopsis around at the moment?

August 8, 2026

The clam beneath Emily Bay

I’ve seen the beautiful shells of Laciolina chloroleuca in Emily Bay for decades, but I’d never really stopped to wonder where the living animals were. It turns out they may be buried half a metre beneath the sand. A closer look at an easily overlooked clam, its extraordinary shell markings, and the hidden life beneath our lagoon.

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.