Kermadec Islands - images of molluscs

By Dr J Floor Anthoni, 2002

The Kermadecs do not have many species of mollusc, but the giant limpet makes up for that. It is found only here, and is perhaps the largest limpet on Earth. In Chile another giant limpet is found. What is surprising is that a tiny shallow water environment is capable of maintaining a viable population. Needless to say that this animal is prone to threats from humans and needs to be protected in full.

It is striking that large areas of rock remain covered in red and green grass-like algae, an indication that the rocks are poorly grazed. Part of the reason is the strong water movement, which wipes organisms off the rock face, but another reason is that the grazing snails are simply not there. A notable exception is the giant limpet (Patella kermadecensis), which grows just under low tide in the wildest of waters. It grazes only a small patch, and returns to its home spot, which its shell has grown to match. This small patch provides it with the scant energy to construct a massive shell. It can do so only by living a long life, but how long is not known. It has solved the problem of finding a partner of the opposite sex, by being female and carrying a small male on her back. This male is confined to graze her shell, which also keeps her clean.

Unfortunately, our visit did not allow enough time to focus on the molluscs, but some interesting nudibranchs have been seen.

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f031408: a narrow zone of giant limpets
f031408: A narrow zone of giant limpets (Patella kermadecensis, Scutellastra k.))  is found on hard rock, just underneath the waves at low tide. It is only a small area, heavily competed for. But these limpets do not move about freely, as can be seen from the enlargement on right.
f031408: Giant limpets beneath wave zone
f31408c: This is an enlargement of the previous image. It clearly shows the giant limpets staying in one spot, and grazing a small area around it. Notice that it is apparently able to scrape the hardy pink paint (Lithothamnion sp.) from the rock, which may provide it with a helpful supply of chalk for its colossal shell. 

f031616: Kermadec giant limpet (Patella kermadecensis)
f031616: In the picture one can see two giant limpets nearby, and a vacated spot, the homing spot of a limpet that died. Notice how nothing grows on this spot, because the shell of the limpet takes all light away. Notice also how difficult it is to see the small males on their backs, but the left limpet's back shows a poorly grazed patch, which gives the male away (on left). The rear limpet however, is poorly grazed all over, perhaps because it does not have a male jockey.
f031810: Large whelk
f031810: An unknown whelk, covered in pink paint, is hardly discernible. (Morula (Neothais) smittii ?)

f030926: Top shells
f030926: Large Kermadec top shells (Tectus royanus) grazing a vertical rock face.
f030926c: Enlargement of top shells
f030926c: Close-up of the shells in previous photo.

f031225: Giant oyster, dead
f031225: Completely hidden, and securely cemented to the rock, one can find these giant oysters, only if one knows what they look like. The oyster shell is very thick and high, providing an excellent grip for divers to hold on to.

f031823: long worm
f031823: A mysterious long worm of 60cm, vividly marked like a coral snake. It apparently has a good defence against being eaten.
Closeup of worm
f031823c: Close-up of the same worm.