“It’s worse than that, it’s dead, Jim”

That’s what ran through my head on seeing this sea urchin in a rock pool at Flat Rock, Ballina, yesterday (why I was thinking of Star Trek, I’ll never know). Its green tube feet were moving quickly, but it wasn’t going anywhere. The orange spines were also moving and it would normally be speeding (if you can call it that) across the sandy rock pool bottom on the tube feet. But this one had met its demise. What it had left for a nervous system was causing the movement –  if you want to know more about what’s inside, go here.

The underside shows, in the centre, the mouthpiece (called the Aristotle’s lantern), which it would have used to scrape algae off the rocks and move it inside the body for digestion.

This one had been thoroughly speared and its guts eaten by a bird, possibly one of the sooty oystercatchers or the eastern reef heron (Egretta sacra albolineatai, dark morph) that was poking its beak into the pools.

Various migratory birds were enjoying a rest or gleaning. They’ll be off to the northern hemisphere in autumn.

There was also a small octopus on its last legs, so to speak, looking very unhealthy in one of the pools. It was upside down, flailing its arms and couldn’t right itself, and when I carefully moved it right-side-up, it didn’t trundle off to shelter like they usually do. Perhaps it was at the end of its life – octopuses often last only a year or so.

All in all, a bit of drama on the rock platform in the hot summer sun.

Sea cucumbers, stars and urchins on Lord Howe

I was going to call this post “the pentaradials”, because sea cucumbers, sea stars, brittle stars and sea urchins all have similar body plans (fivefold symmetry), but decided I was trying too hard. It’s a good excuse to group them together, though.

Sea cucumbers

The black sea cucumber (Holothuria leucospilota) common on Lord Howe is the same one as on the coast at home. I’d often wondered what the internal structure of a sea cucumber was, and as luck would have it (although not for the sea cucumber), there was a dead one on the beach.

What’s inside a black sea cucumber

When you disturb one, it’ll sometimes spit out white stringy filaments – these are the Cuvier’s tubules, the white stuff on the left of the picture. They become very sticky on contact with water and are apparently toxic, so a defense mechanism for this animal. I didn’t realise there was so much of them inside. The sausage-looking structure is indeed the intestine. One of the other structures is the respiratory tree, the equivalent to our lungs.

[Update: you can see the internal structure of a sea cucumber and find out about its eating habits at Deep Sea News here.]

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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

Shining symmetry

Sea urchins are beautiful and fascinating, whether alive or dead. Some would say delicious, too, but I haven’t sampled them, despite living and working in Japan and Hong Kong for a bit and backpacking solo all over South-East Asia for three months.

Sunshine through sea urchin

Hundreds of little hydraulic-driven feet move them about, and are protected by their spines.

Sea urchin (Tripneustes gratilla?) at Flat Rock, Ballina

Pink sea urchin, photo by Mo Dickson

You can see the little tube feet between the spines in the pink sea urchin (Holopneustes pycnotilus, sometimes called the thickened sea urchin) above.  According to Davey’s A Photographic Guide to Seashore Life, it is confined to NSW between the Richmond River and Ulladulla (south of Sydney). This one is from Flat Rock, just north of where the Richmond River comes out into the sea at Ballina.

The photo below (Heliocidaris erythrogramma?) shows, in the centre, the ‘Aristotle’s lantern‘ – the hard central mouthparts – which the animal uses to scrape off algae for eating.

Worse for wear, but still alive and kicking, photo by Mo Dickson

The red-spined sea urchin (Holopneustes porosissimus, below) is ‘almost always found wrapped up in algal fronds during feeding’ (according to Sea Stars of Australasia and their Relatives, by Coleman).

 

Red-spined sea urchin

Sea shell, sea shell, sing a song for me
Tell me about the ocean, tell me about the sea.