High noon, low tide at the rock pools

Around spring equinox, the low tides are lower than usual. The sand deposited by winter storms is starting to be washed off the rocks, and there is now lots of life in the Flat Rock rock pools, although surprisingly few humans on the beach, considering it is the start of a fortnight of school holidays.

I can’t resist a nudibranch, even though I’ve already posted another photo of this one, Rostanga arbutus

Nudibranch, Rostanga arbutus

I’ll not post photos of the larger turbans and sea hareDolabrifera brazieri, that were there, as I’ve already put photos of them up. It’s great to see so many large, live shells such as tritons and turbans.

But here’s a new find – an empty Port Jackson (Heterodontus portusjacksoni) shark egg, which was originally lodged in a crevice and mostly covered with sand.

Port Jackson shark egg

The egg cases are usually dried out and hard when you find them, although soft when the female shark lays them. These small sharks lay 10 to 16 eggs and push them into cracks in rocks or under ledges. These eggs take about a year to hatch, and so the empty egg-cases wash ashore in winter or spring.

I’m not sure what the orange things below are – sea squirts (ascidians)? Sponges? Interesting, anyway. I love a natural history mystery, and I love solving it even more. Haven’t cracked this one yet.

Orange sea squirts?

Here’s a sand collar, once containing the eggs of the common sand snail, Polinices didyma. The eggs from the sand collar hatch into larvae and float around in the water for a while, developing into the carnivorous snails that move around in the sand searching for prey to drill, poison and eat.

Sand collar, containing the eggs of a sand snail

I flipped a rock, and under it was a brittle star, about 22 cm from tip to tip …

Brittle star

It scooted away, revealing these fireworms (one of the Eurythoe species). Do not touch these, as the bristles break off easily, lodge in your skin, and they’ve not called ‘fireworms’ for nothing!


This rock crab was very lively, despite having lost its right claw.

Rock crab

These are intriguing – I’m guessing they are hydroids of some kind …


This cone, Conus ebraeus, would have chased down and eaten worms when it was alive …

The worm-eating Conus ebraeus

The shell Peristernia (Nodopelagia) brazieri sits on top of a colony of  tubeworms (Galeolaria caespitosa) …

Peristernia (Nodopelagia) brazieri on tubewom, Galeolaria caespitosa

There were many Australian red tritons, Charonia lampas – this one has chitons, Isochiton australis, on the left.

Charonia lampas with chitons

Here’s C. lampas in its pool – you can see the eyestalks and siphon …

C. lampas at home - note the eye-stalks and siphon

And lastly, this jelly-looking thing is a black-and-white flatworm, found under a rock. I wasn’t fast enough to get a shot as it swam away.

Flatworm (centre)

A good way to spend a spring equinox day.

7 thoughts on “High noon, low tide at the rock pools

  1. Joy – on your pic of the flatworm, what do you think that aworm in te top right corner is? If you have any idea, I am seeing a ot of them and would love to know thanks! ~Karen

    • Hi Karen,
      do you mean the narrow white one? It is probably the lime tube of the so-called “Sydney coral”, Galeolaria caespitosa. It isn’t a coral, but a tube worm. You often find them in huge masses – see http://en.wikipedia.org/wiki/Galeolaria. Recent DNA research indicates there are actually two species of what used to be thought of as this one species. The worms have fan-like structures which they use to filter food out of the water when the tide is over them. Otherwise they are clamped shut to stop drying out.

  2. Pingback: 5 Phyla to Identify in a Tide Pool – Bio by the Bay

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