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.

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.

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)

November 3, 2026

Familiar faces – getting to know the reef’s residents

Six years of swimming the same little reef have introduced me to some unforgettable characters that I’ve followed over time. From familiar fish and anemones to turtles and a snail’s eggs, this final article in my photographic series explores what I’ve learned about the lives of individual animals simply by returning, watching and taking photographs.

November 1, 2026

When algae move in – the changing reef neighbourhood

Algae are a natural part of Norfolk Island's reef, changing with the underwater seasons. But sometimes their beautiful green growth conceals a rather sad story. In the fifth article of my six-part photographic series, I revisit familiar places to see how algae have changed over the years – and what might be hiding underneath.

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?