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.

Here’s a shot showing more details of the mouth. It’s trundling along in the direction of the bottom right, and is about 2.5 cm long. When I gently touched the back, there was a firm shell underneath but the mantle did not retract.

An active and fast mover, so probably a hunter

You can also see attractive small giant clams (Tridacna maxima), 15 or so centimetres long, embedded in the reef. I like the name – they really are called “small giant clams”, as opposed to being just small “giant clams”, if you get my drift. The varying patterns and colours on the giant clams are delightful. They filter water for oxygen and food, and have growing in their flesh algae  which photosynthesise, supplying them with sugars from that process. I hate to think of them being hacked out of the reef for the aquarium trade, but that’s what happens in some parts of the world. These lucky clams are in a protected World Heritage-listed area.

Elongated giant clam

This is what the dead clam shell looks like …

Empty shell of small giant clam

The algae-eating turban Turbo cepoides has been found only on LHI and Elizabeth and Middleton reefs to the north of Lord Howe …

Turbo cepoides

Note the distinctive operculum (door) - you can tell a turban species by its operculum

The operculum of T. cepoides grows in size along with the animal

Underside (the side attached to the foot of the animal) of T. cepoides operculums. The brown wears off eventually after death.

The ringed cowrie (Cypraea  annulus) is the same species as ours …

Ringed cowrie, snuggling with a couple of sea cucumbers under a rock

… as is the black nerite (Nerita  atramentosa). This one shows a fatal attack by, possibly, a moon snail (Polinices species). According to Ian Hutton’s “A Field Guide to the Marine Life of Lord Howe Island”, the moon snail produces a neat, round, countersunk hole courtesy of its radula (pad of sharp, scraping teeth) and secretion of acid. The holes made by octopuses gnawing their way through the shell are much more ragged.

Black nerite, possibly drilled by a moon snail

Another cowrie I found is the milk spot cowrie (Cypraea vitellus) …

Milk spot cowrie

Underside of milk spot cowrie

Apparently there are no large shells there as the parrot fish and wrasses would make short work of them – having seen parrot fish breaking off and gobbling up coral enthusiastically, I can imagine that. They even make mince-meat of some (not all, as there are plenty left) of the urchins with very long, supposedly protective spines.

Hooray, something that my own patch does better than Lord Howe – large shells!

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3 Responses to Shells in Lord Howe Island rock pools

  1. ashbycath says:

    Small Giant Clam, OK. Good example of an oxymoron if I ever heard one.

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