Heroes of the beach – sea cucumbers

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.

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The beautiful sand of Emily Bay, Norfolk Island, didn’t get there by accident. It is the direct result of the hard pooping work of generations of marine animals, including among other things, parrotfish (see my blog post The Sand Poopers) and sea cucumbers.

I confess to not having paid much attention to sea cucumbers until recently. And only now am I doing so because they seem to be on the wane inside our lagoons. A few people have asked me where they have gone. I have no idea, but one thing I do know is that they are important members of our ecosystem on many different levels. For example, they clean and aerate the sand, plus, there are some quite rare critters in our lagoons, such as the Tonna melanostoma (a type of mollusc), whose only food is the sea cucumber.

But first some fast facts:

they are part of a family called echinoderms (great article!), along with sea stars and sea urchins
they have tube feet, like tentacles, that they use to move
they breathe through their anus
they feed on the algae and tiny marine creatures found in the sand that they shovel in using the little tube feet that surround their mouths
as a defence they will propel their own toxic internal organs from their bodies (eviscerate) at their attacker
they reproduce both sexually – which is more usual – by releasing eggs (females) and sperm (males) into the water column at the same time, and asexually, by splitting in two
they can live for between five to ten years
they live on the sea floor
they can grow as big as 1.8 metres in length
they are considered a delicacy in some cultures and can therefore be subject to overfishing.

So, putting aside the part of me that finds these things a little unappealing, I thought I’d do some research and find out exactly what part sea cucumbers play in the ecosystem here on Norfolk Island’s reef.

And, to be honest, I couldn’t go past this brilliant description of their role, posted by the Melbourne-based environmental group Remember The Wild on their Facebook page.

Sea cucumbers are far more active than you might believe of an animal named after a table vegetable, and play an important role in nutrient cycling in marine ecosystems!

As they slowly slug their way across the seafloor, looking like various colourful sausages, they eat algae-covered sand and strip out the organic matter for their dinner.

Behind them they leave trails or piles of the cleanest sand imaginable, like tiny streetsweepers.

As they eat their way around the reef, they reduce the levels of decaying organic matter in the environment, recycling it into useful nutrients (like phosphorus and nitrogen) for other animals and plants.

As they churn through the sand, they help mix oxygen through the layers, helping the tiny lifeforms that live in the sediment grow and prosper.

You see, despite their size, slow lifestyle and lack of brain, sea cucumbers have a massive role in their environment and are vital for healthy reefs!

So next time you’re marvelling at the purity of the fine white sand on that tropical beach, remember that you’re actually sitting on a lovely beach of poo, and thank your local sea cucumbers for their service.

Class Holothuroidea

Light-spotted sea cucumber - Holothuria hilla

Class Holothuroidea

Black sea cucumber - Holothuria leucospilota)

Class Holothuroidea

One of the things that coral reefs need for their health is nitrogen. As the sea cucumbers sift through the sand, they release the nitrogen that is trapped there, making it available to the corals.

The mouth of a sea cucumber “vacuuming” the sand for particles of food.

Another curious fact about sea cucumbers is that some of them have a fish, the pearlfish, living in their anus (or cloaca). The pearlfish’s delicate, slender body is protected by the sea cucumber. To each his own, I say!

We have a few different species of these squishy, sausage-like animals, but I’ve not been able to get definitive IDs on all of them. There are around 1250 known species. I would think that Norfolk Island’s lagoons are not well studied in terms of what sea cucumbers live here.

I have certainly gained a new respect for these creatures. We need them. And we need to love them, along with all the other important species that make up the web of life on our reef.

Here’s some further reading and watching:

Sea cucumbers are critical for healthy ocean ecosystems (article)
Sea cucumbers: The excremental heroes of coral reef ecosystems (article)
Why sea cucumbers are so expensive (short film clip)

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.

April 5, 2026

What Norfolk Island’s reef tells us about environmental blind spots

The Kingston dredging proposal on Norfolk Island raises a bigger question than dredging alone: how well do standard environmental assessment tools capture the real significance of a remote and unusual reef system like Norfolk Island’s?