Shells in Lord Howe Island rock pools

Lord Howe has many marine species similar to those in other parts of the Pacific – the eggs and larvae get washed along in currents from other places, and survive to adulthood if they don’t get eaten or if they find a place that suits their needs.

Survival pressures can also push species to evolve into new ones that occur only in the “new” home (by then not at all new). In other cases, such changes do not proceed because the conditions already suit.

My favourite rock platform find is probably this cowrie, Staphylaea limacina (many thanks to Sallyann Gudge, Lord Howe Island Marine Park Marine Ranger, and the Australian Museum for confirming the ID).

Many cowries have elongated papillae like these.

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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

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A sauntering sea hare and a tiny nudibranch

Yesterday I saw this very charming sea hare, Dolabrifera brazieri, moseying across a shallow pond and grazing on algae, again at Flat Rock, near Ballina, northern New South Wales. It’s about 9 cm when stretched out.

The sea hare, Dolabrifera brazieri

Sea hares are molluscs and have internal shells. They are generally regarded as toxic, and are reported to have killed dogs that have eaten them. They exude a purple dye if they are upset. Some species form head-to-tail chains to reproduce in the warm waters of late summer. They live only a year or so – fast growers.

I first thought the minute orange nudibranch below was Berthellina citrina, which is a side-gilled sea slug and does not have the ‘naked gills’ you can see at the rear of the creature in the second photo below. The top photo shows the size out of water, so scrunched up. The black dots are rhinophores, which are scent or taste receptors  (not eye spots). Rhinophores come in all sorts of amazing shapes, sizes and colours.

Mystery solved - Rostanga arbutus

The photo below shows the nudi in water, and the gills are visible at the back. It looks yellow in the photo, but actually is orange/red as above. Nudibranch expert Gary Cobb says it’s Rostanga arbutus.

Rostanga arbutus

Another side-gilled sea slug, seen on an earlier visit, is Pleurobranchus peroni (thanks to Gary again for the correction to my ID). You can see the shell through the semitransparent skin on the back. The ‘side gill’ is under the mantle.

Side-gilled sea slug, Pleurobranchus peroni

A further live shell of interest seen on a previous visit is the umbrella shell, Umbraculum umbraculum (thanks to Gary for the correction). The white thing in the middle of its back is its shell. It cannot contract into it, hence the term ‘umbrella’ – but maybe ‘parasol shell’ would have been a better name.

Umbrella shell

I once read a piece about a diver who decided to test the theory that brightly coloured nudibranchs advertise the fact that they taste awful by putting one in his mouth. He confirmed it – a braver man than me.

Final gloomy day creatures

Continuing from the previous two posts …

Carnivorous shells abound, but some herbivores are big and tough enough to survive – for instance, turbans. The turban below (left, Turbo militaris) is about the same size as its nemesis (right, Australian red triton, Charonia lampas)  and has a massively thick, protective shell. So does the triton.

Not exactly friends - the right would eat the left

And to show the actual sizes …

Big imperial turban (left) and big Australian red triton (right)

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More gloomy day creatures

Continuing from the previous post

It must have been a hermit crabs’ convention, as there were dozens and dozens. Perhaps they were there en masse to trade shells (they swap into larger shells as they grow) or mate, or just because there was a lot to eat. We saw close encounters, but perhaps that was because of the sheer numbers.

Hermit crab, Dardanus crassimanus

Hermit crab, Clibanarius viriscens, inside a Spengler's triton

Hermit crab, Dardanus crassimanus

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Alive, alive-o!

It’s great to see a sea shell (mollusc), but even better to see the animal that made it, intact and getting on with its life. ‘Shell’ is a bit misleading, as many molluscs don’t have visible shells but are photogenic anyway.

I learned a lot of what I know about molluscs, both salty and fresh, from a book called The Shell Makers: Introducing Mollusks, by Alan Solem. Although it’s quite old (1974) and written by a mollusc expert who was Curator of Invertebrates at the Field Museum of Natural History, Chicago, it is far from dry. It is very detailed about the classification, structure and lifestyles of the animals themselves in all their forms (bivalves, chitons, gastropods, limpets, octopuses and their relatives, and so on, both fresh and salt water), with chapter titles like ‘To scrape a living’ (about feeding) and ‘On becoming sluggish’ (about, well, slugs). He describes the actual process of forming a shell, and there are many photos of the actual animals.

My partner-in-crime on the beach is my husband, Andrew. He’s an octopus-spotter par excellence, even when they are sheltering under their ledges in the daytime. The octopus is one of the photogenic molluscs that don’t have any shell, internal or external.

I was asleep, but I just came out to see what you’re up to

Here’s Andrew with an elephant snail, Scutus antipodes.

Andrew and elephant snail at Flat Rock, Ballina

Here’s a close-up  of Scutus antipodes.

Close-up of an elephant snail

You can often find the shell of a dead Scutus on the beach or in a rock pool.

What’s left after an elephant snail dies

Charonia lampas, the Australian red triton, is a common mollusc found in crevices in rock platforms around here. If you go at the lowest tides of the year (at the spring or autumn equinox), you can investigate places that are normally covered up by water.

Australian red triton

And then there is the ringed cowry, Cypraea annulus.

Ringed cowry

Here’s something to be very careful of. Treat any live cone shell (below) with extreme caution, as some species have killed people. They sense their prey with their proboscis and eye stalks (the pair is visible below), hunt it and impale it with their harpoon. The venom paralyzes the prey, and the cone then extends its mouth to swallow it. Not all cones kill people, but enough people have been harpooned and died that you should not pick one up, and especially not put it in a trouser pocket or in your swimsuit! They are pretty, but a ‘look, don’t touch’ policy is best.

Beware the harpoon of the strawberry conch, Strombus luhuanus – both eye stalks are visible above

 

I’ve posted pics of other live molluscs in previous posts: nudibranchs, turbans, bubble shells and sea hares.

I’m looking forward to learning more about molluscs, this time land ones, when I receive my copy of The Sound of a Wild Snail Eating. This book has had great reviews.

In the meantime, to paraphrase a song, I’ll be going:

Along beaches broad and narrow

Crying cockles and mussels

Alive, alive-o

A tasty feast – for a bird

Shorebirds like oystercatchers make meals of limpets and chitons that sit on rocks, clamped down to conserve their water when the tide is out, like the one below.

Potential shorebird munchies - a chiton

How the heck a bird recognised the camouflaged chiton below flummoxes me.

Camouflaged chiton

But it did, and this is the result.

Inside a chiton

A flipped-over limpet is usually left squeaky clean, with no wasted bits of flesh, so I’m not sure why this chiton has just had its foot pecked away or whether any internals have been taken. Perhaps the bird took a peck and decided it wasn’t so tasty after all.

More sea shells by the sea shore

Nerites

Many algae- and lichen-eating snails hang about in rock pools but are found stranded when the tide goes out. They shut tight their operculums (‘doors’) to protect themselves from dessication and birds. They feed by scraping off algae and lichen on rock surfaces with their radula (mouthparts that have little hooks like Velcro) and are in turn eaten by predatory shells that drill a hole in their thick shells, and birds like oystercatchers. They lay egg capsules on rocks and other shells; the hatchling larvae float about in the water and after a few months settle back on the rocks and continue their development into adults. Nerites comprise one such group.

Black nerite, Nerita atramentosa

Periwinkles

Periwinkles live a similar life to nerites. In the photo below, you can see black nerites (the one on the bottom left has a Nodilittorina pyramidalis on top) and the periwinkles Austrocochlea porcata (with wide stripes) and Austrocochlea concamerata (narrow stripes).

According to Australian Marine Life (Edgar, 1997, Reed Books, p. 245), Nodilittorina unifasciata is the most abundant mollusc  on temperate Australian seashores.

The periwinkle, Nodilittorina unifasciata

Nodilittorina pyramidalis is another common periwinkle.

Nodilittorina pyramidalis

It has obviously read the field guides as it conforms to what Edgar says: ‘ the species is rarely found on flat rock surfaces, preferring sandstone that has weathered into a honeycomb structure’ (p. 246).

N. unifasciata and N. pyramidalis on honeycomb sandstone

Turbans

There are three species of turban shells in the pools at Woody: from largest to smallest, Turbo militaris, Turbo torquatus and Turbo undulatus.

Turbo undulatus - note the shape of the operculum, unique to this species

The operculums on these turbans are all very thick and strong. You can often find them on their own, as they detach from the flesh of the animal after it dies and rots away. A friend thought they were the remains of independent shells themselves. The shape and colour are unique to each species.

Turban operculums

In the photo above, the top row shows the outer surface presented when the turban clams up. The left column is Turbo militaris and the right, Turbo torquatus. The photo below shows the detail of the ‘inside’ of the torquatus operculum. It is quite rough.

Surface texture of operculum of T. torquatus

Turban shells are herbivores and live in the crevices of the rock platform, under the water line. Humans find them edible, as do shorebirds, lobsters, crabs, starfish and predatory marine snails.

Live Turbo militaris with intact operculum

The local Aboriginal people called turbans ‘gugumbal’ and you can find out about how they ate them at www.arrawarraculture.com.au/fact_sheets/pdfs/05_Gugumbal.pdf

The turban is a classic example of a herbivore – a National Parks guide once told me that if the opening of a shell is round, it’s a herbivore. If not, it’s a carnivore. I myself find that whether there is a groove in the shell for its ‘harpoon’ is a more reliable characteristic, but ‘roundness’ is a pretty good start. Moon snails (see The joys of beachcombing) appear to be an exception to the rule – they are round carnivores.

I’ll continue with molluscs in a later post.

Egg masses and rams’ horns

Woody Head, Flat Rock and just about any other sandy beach, especially if it has a rock platform, are places of treasure for the sharp-eyed. The more types of environment, the more you will see. And the more often you go there and look, the more you will see. Finds are like the pieces of giant 3D jigsaw puzzles, giving you clues about the lives of plants and animals that live there, and their interrelationships. All you have to do is put it together.

For instance, you may see what looks like a bit of congealed sand washed up on the beach. It’s actually the egg mass of a mollusc. Apologies that it’s slightly out of focus, but you get the idea.

Moon snail sand collar

Each species of moon snail (species of Polinices) has a very recognisable egg mass, sometimes washed up. Polinices sordidus produces egg ‘sausages’ and Polinices didymus sand collars.

Egg sausage of Polinices sordidus

There’s a good photo of a floating egg sausage here.

Polinices didymus, producer of the sand collar egg mass

Moon snails are also called ‘sand-plough snails’, because that’s exactly what they do in pursuit of their prey, other snails. They drill a hole in the prey shell and scrape away at the flesh with their ‘radula’.

If you find what looks like orange spaghetti on the beach, it’s the egg mass of the sea hare (Aplysia dactylomela).

Aplysia dactylomela egg mass

And here’s the culprit.

The sea hare Aplysia dactylomela, munching its way through algae in a nearby rock pool

Another washed-up shell is the ram’s horn – actually the ballast chamber of a deep-sea squid-like creature, Spirula spirula. Open-ocean goose barnacles often attach themselves to the floating shell.

Ram's horn with goose barnacles

I’ll post more photos from time to time as I find interesting things.