Creature of the week
Oyster borer
Haustrum scobina
20 - 27mm long.
The Oyster
borer
Haustrum scobina, is a type of predatory sea snail or rock snail.
Description: The oyster borer is fairly small with a tubby spiral shell, roughly
sculptured and speckled grey and white. The shell opening is chocolate brown with a
white edge.
Habitat:
Live on the rocky shore at mid –to high tide level where their prey are
plentiful - barnacles, oysters, mussels. This area does dry out, but they can survive by
using a mucus layer around the entrance door (operculum) to seal it.
Diet: Small, yet deadly, oyster borers force open the protective plates of barnacles with
their muscular foot, and insert their long finger-like proboscis into the flesh to consume
it. When attacking shellfish such as oysters, they drill the shell with their file-like teeth
radula, as well as adding some acid mucus that dissolves calcium of the shell - taking
anywhere between 45 minutes to two days to reach the succulent meat inside. When there
is plenty of food, the oyster borers grow large and lead separate lives. When food is
scarce, they hunt in packs, taking the younger of their species with them to attack the
few available prey. Probably to show them how it is done?
Reproduction: Spawning occurs a month after fertilization. Many white or purple
capsules, each containing about 200 eggs, are laid under rocks. Most of the embryos
(95%) break down into a yolk-like mass, creating food for the survivors.
Conservation
issue: Near ports
and marinas, the
rock borer has
disappeared due to
the chemical TBT in
antifouling paint,
which sterilises the
males. This
chemical is now
banned from such
marine paints.
References:
 Miller M & Batt G, Reef and Beach Life of New Zealand, William Collins (New
Zealand) Ltd, Auckland, New Zealand 1973
 Powell A. W. B., New Zealand Mollusca, William Collins Publishers Ltd, Auckland,
New Zealand 1979 ISBN 0-00-216906-1
 Margaret S Morley, Sea shells of New Zealand, New Holland Publishers (N.Z.)Ltd
 Dr Peter Jenkins, Marine Diversity Photographs.( Personal to Sir Peter Blake MERC)