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.
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
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: 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: An unknown whelk, covered in pink paint, is hardly
discernible. (Morula (Neothais) smittii ?)
f030926: Large Kermadec top shells (Tectus royanus)
grazing a vertical rock face.
f030926c: Close-up of the shells in previous photo.
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: A mysterious long worm of 60cm, vividly marked like
a coral snake. It apparently has a good defence against being eaten.