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.
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)