Poop power — 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.

There’s no polite way to say this, so I’m just going to come out with it: coral reefs run on poop. OK, maybe ‘run’ is a bit of an exaggeration but, certainly, faeces, from marine animals such as fish and seabirds, plays a significant role in supporting coral reef ecosystems.

Yes – poop. Fish poop. Bird poop. It's all part of the invisible machinery that helps coral reefs function.

Let’s start with fish. Every day, thousands of reef fish cruise the coral gardens, nibbling, grazing, or chomping their way through algae, plankton, and even coral. What goes in must come out, and when it does, it’s often in the form of little nutrient packages that fertilise the reef. Some fish, like parrotfish, even poop out sand. (In fact, in some places like Hawaii, a significant portion of the beach beneath your towel is technically parrotfish poo. See my blog post The Sand Poopers.)

But it’s not just about fertilising the reef or topping up the sandbanks. Fish poo – particularly from herbivores – is food for other species. Recent research has shown that certain reef fish will actually eat the faeces of their neighbours. It might sound gross, but in a nutrient-limited environment like a coral reef, nothing goes to waste. It’s all part of a tight recycling loop that keeps the whole system going.

Birds get in on the act too. Seabirds feed far out at sea and return to their island rookeries to roost, depositing nitrogen-rich guano on the land. When it rains, that guano trickles into the sea, supercharging nearby coral reefs with extra nutrients. This isn’t just theory – scientists have found that reefs near seabird islands are healthier, with faster-growing corals and more abundant fish. The whole reef community gets a lift from these nutrient deliveries.

So, we can see that fish poop supports the reef – fuelling coral growth, feeding other animals, even helping shape the sandy beaches we love. while bird guano, delivered from far-off feeding trips at sea, brings in nutrients that supercharge the ecosystem. It’s a kind of natural fertiliser conveyor belt, running from the sky to the sea.

However, where there are seabirds there are often rats – introduced into the mix often by accident, via passing ships or visiting humans. They feast on eggs, chicks, and even adult birds, reducing the numbers of seabirds. With fewer seabirds, the flow of guano slows. And without that nutrient boost, the nearby reef ecosystems begin to suffer. Studies have shown that fish biomass can be 50 per cent lower around rat-infested islands compared to rat-free ones. That’s a big drop for something most people have never even heard of.

Some of the most productive and biodiverse reefs are those near seabird islands – provided the birds are left undisturbed. When rats invade and drive birds away, the nutrient flow stops. It’s a reminder that reef health isn’t just about what happens underwater – it depends on the whole system working together.

Here on Norfolk Island, we have two other islands in our remote group, Nepean Island and Phillip Island, plus a number of small islets that are remnants of the island’s volcanic origins immediately off the coast, particularly along the northern and western shore. These are all important safe havens for seabird breeding colonies. So far they have remained rat and cat free, making them important not just for the seabirds themselves but also for the ecosystems that are interconnected with them, including our inshore coral reef area.

From the fish that poop sand, to the birds that fertilise the sea with guano – and even the fish that eat other fish’s droppings – the reef is a tightly connected web. And while it might not be glamorous, poop is one of the most important links in that web.

So next time you’re snorkelling and a fish lets one go right in front of you … take it as a sign that the reef is doing what it’s meant to.

Above: a banded scalyfin (Parma polylepis) lets one fly. This damselfish is part of the reef’s recycling crew, farming algae and fertilising the neighbourhood as it goes.

Good poop, bad poop

I can hear the questions about the difference between the faeces of fish, birds, human and cattle, so it would be remiss of me not to address this. Here’s a very quick summary.

You’d think that if a bit of bird poo is good for corals, then a bit of human waste might be too. After all, it’s all just nutrients, right? Not quite. It turns out that not all poop is created equal.

Fish and bird waste are part of the natural cycle. This waste is released in small amounts and taken up quickly by plants, corals, or other animals. But human sewage and livestock runoff come in much larger quantities, and often during storms or floods when septic tanks overflow or paddocks are flushed into the sea. These pulses overwhelm the reef.

They also contain things reef ecosystems haven’t evolved to deal with: pathogens that can infect corals, pharmaceuticals that disrupt fish behaviour, and nutrients at concentrations high enough to fuel algal blooms that smother coral and suck the oxygen out of the water.

In short, fish poop supports the reef. Our poop, when it reaches the ocean untreated or in excess, unravels it.

Want to dive deeper?

Grupstra, C. G. B., et al. (2023). Consumer feces impact coral health in guild-specific ways. Frontiers in Marine Science, 10, 1110346. https://doi.org/10.3389/fmars.2023.1110346
van der Heijden, L. H., et al. (2022). Feces consumption by nominally herbivorous fishes in the Caribbean: Coprophagy as a nutrient cycling mechanism. Coral Reefs, 41(1), 1–12. https://doi.org/10.1007/s00338-022-02228-9
Lavers, J. L., et al. (2018, July 12). Rats are damaging coral reefs by attacking seabirds. ABC Science. https://www.abc.net.au/news/science/2018-07-12/pests-rats-damaging-coral-reefs-great-barrier-reef/9957628
Sidley, P. (2018, July 12). Bird poop helps keep coral reefs healthy, but rats are interfering. Science News Explores. https://www.snexplores.org/article/bird-poop-helps-keep-coral-reefs-healthy-rats-are-interfering
National Oceanic and Atmospheric Administration. (n.d.). How does land-based pollution threaten coral reefs? NOAA National Ocean Service. https://oceanservice.noaa.gov/facts/coral-pollution.html
Reef Builders. (2023, April 28). New study finds herbivore fish poo is bad for corals (sometimes). Reef Builders. https://reefbuilders.com/2023/04/28/new-study-finds-herbivore-fish-poo-is-bad-for-corals/

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?