A gloomy day, full of life

Perhaps the heavily overcast conditions on Saturday fooled the critters at Flat Rock into thinking that it was dusk and wake-up time, but I have rarely seen so much life in the rock pools in one session.

For starters, we found five common Sydney octopuses (Octopus tetricus)! There were a couple in the same pool, but apart from each other. The white eyes are definitive of that species.

Common Sydney octopus

They all matched the colour and texture of the main seaweed in the pool, even becoming more or less ‘spiky’ as they moved fluidly across the bottom.

According to Norman and Reid’s A Guide to Squid, Cuttlefish and Octopuses of Australia, they can have an armspan of two metres, but these would have been only about one metre. This octopus ‘feeds on shellfish, which it drills and poisons, then pulls the shells open and eats the paralysed contents. This species primarily emerges at night to hunt crustaceans and gather shellfish. … Lairs can often be recognised by the bivalve shells scattered around their entrance’.

I’ve also seen the blue-lined octopus (Hapalochlaena fasciata) on this reef, but not yesterday. It was glowing blue at the time, so I left it well alone. I was slightly worried as their bites are reportedly painless, and inject a toxin that causes paralysis. If you can be kept breathing, you’ll be OK. Otherwise – not.

Another exciting find was more than 15 (I stopped counting) little ruby flatworms (Phrikoceros baibaiye). They are bright orange with small white spots and very active.  The edge of the mantle is very mobile. The head on the one below is on the left. We found one (or was it two?) appearing to chase its tail, going round and round in a swirl of skirts. Was it two mating, one laying eggs or just playing ouroboros?

Little ruby flatworm

Size of flatworm compared to Austrocochlea shell, photo by Andrew Roberts

While gazing at one flatworm, I became aware of a black nudibranch (Dendrodoris nigra) near it. Then I spotted a second black nudi nearby! You can just see the ‘naked gills’ at the back (top) of the nudi below.

Orange flatworm and black nudibranch

Another colourful inhabitant out feeding was the orange feather duster below. You can see the tube it withdraws into when it needs protection.

Orange feather duster worm

Here’s a sea urchin (Tripneustes gratilla?). It was camouflaging itself with seaweed so was barely visible in its pool.

Size comparison

When I put it back in the water, it put its feet out to move back to shelter (where I placed it in a more hidden spot after the photo).

Sidling away on a multitude of feet

Last (for this post – I’ll continue in another one as there was lots to see), I inadvertently startled a black sea cucumber, and it ejected its tubules of Cuvier in defense. These are quite sticky on the fingers. The animal regrows them.

Black sea cucumber ejecting tubules of Cuvier as a defense

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3 Responses to A gloomy day, full of life

  1. Rebecca says:

    I had to Google “tubules of Cuvier” – here I’d been laboring under the misapprehension that sea cucumbers vomit up their intestines, but instead they expel part of their respiratory system out of their butt. Nature is very weird.

  2. Cath Clark says:

    Shiny & gorgeous zebra volute, wow! Some amazing pics there, Joy. Also loved the Ruby flatworms & tubules of Cuvier… You’ve quite the treasure chest out there at FlatRock.

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