f007212: the barren zone is started by a large storm, removing
kelp from areas that are too exposed for them. Sea urchins then move in
to maintain the barren patch, and to enlarge it. Evechinus chloroticus
f013229: urchins attacking stalked kelp. Once the kelp starts
bleeding, other urchins are attracted by smell. Evechinus chloroticus
f001319: urchins (Evechinus chloroticus) have cleared
an area, and other grazers move in. In the background the sturdy and powerful
grazers, the Cooks turband shell (Cookia sulcata), grazing into
the bushy form of the stone-leaf alga, also called pink paint (Lithothamnion).
The smooth bits are grazed by top shells, catseye (Turbo smaragdus)
and radiate limpets (Cellana radians), all just visible under their
coats of pink paint.
f001932: where the rocks slope gently inside the urchin's
habitat zone, one may find large barren areas like the one shown here.
Some urchins have clustered on the sheltered side of the rock, but a leatherjacket
visits them for a nip at their tubefeet and spines. Although the rocks
look barren, they are nevertheless highly productive, as borne out by the
numerous other grazers found here.
f006828: the last Mohican? Evechinus chloroticus
f019724: an urchin has climbed halfway up a stalked kelp
where it will bite through the stipe, bringing its crown down. The urchin's
five-pronged teeth are only just visible.
f020710: a juvenile needle urchin has five white sectors.
Here it is seen browsing over a tapestry of carpet sponges. These urchins
do not graze , but they catch live prey inside their very agile spines.
f020712: closeup of the juvenile needle urchin shown left
f031117: although still spectacular, the mature needle urchin
has less variety in colour.
f030417: the blue needle urchin is rarely seen.
f020134: the purple urchin (also called black urchin) (Centrostephanus
rodgersii) has thick, sturdy spines. It prefers the clearer waters
of the offshore islands of New Zealand, and occurs a little deeper than
the common urchin.
f021819: because of its larger spines, the purple urchin
can give good protection to juvenile fish, like these young two-spot demoiselles
dispilus). Centrostephanus rodgersii
f030424: in this closeup of the purple urchin the purple
colour and greenish sheen can clearly be seen. Centrostephanus rodgersii
f029818: this white-spined urchin is occasionally found around
our offshore islands (Tripneustes sp?). It stands out by the sheer
density of its red tube feet.
f029825: the white-spined urchin is found from 3-25m, covering
a wide range and an equally wide range of diets. Rather than grazing on
barren rock, it prefers the lush growth of fleshy seaweeds like sea lettuce
and stalked kelp. Here it is seen hoarding its next meal on its back. Deeper
down it climbs the kelp to feed on its fronds.
f004901: the ambush star or elevated cushion star (Stegnaster
inflatus) has a peculiar but effective way of catching prey. By standing
tippy-toed on its five arms, it forms an apparently safe shelter underneath.
The catseye snaill in the foreground might be tempted to walk in. But as
soon as the star's belly is tickled, it closes its web like the curtains
of a stage, trapping the animal inside. Rasplike protrusions on its belly,
move the victim further towards the stomach in the middle, as it fights
to escape. This animal catches snails, crabs, shrimps, seahorses and small
f014730: a collection of ambush stars, brought together
to show their range of gaudy colours. For good measure, two common cushion
stars (Patiriella regularis) are part of the scene. [A6]
f004904: When removed from its site, an ambush star curls
its cardboard-thin web, which makes it more difficult to be eaten.
f001618: a large seven-armed prickly star (Astrostole
scabra) has wedged itself in a crevice, while hiding its prey from
prying eyes. Astrostole is perhaps the largest star known in New Zealand
waters. It can grow to a diameter of 60cm. Its tubefeet are very strong,
and when it is attached to a diver's wetsuit, is almost impossible to remove.
f001615: by gently bending one arm back, the hapless sea
urchin can be seen underneath. But collectively, sea urchins are capable
of fending off this strong predator. Among the urchin's tubefeet covering
its back, are defensive tubefeet with three-pronged beaks. They appear
to hurt the very much larger predatory star. Astrostole scabra
f013820: a Japanese student holds up a seven-armed star to
show its size and what it is eating, a fully grown Cooks turban snail.
f013822: closeup of the seven-armed star and its meal. Astrostole
f010702: a seven-armed star has suffered size reduction by
the predating trumpet whelk (Charonia) who specialises on sea stars.
After giving a star chase with large steps, the trumpet whelk pins it down
with its large siphon, then steps onto the immobilised arm. Realising it
has been trapped, the starfish then sacrifices its arm, running away with
the others. But the trumpet whelk is persisten in its hunt, as this star
has found out, but some of its arms are regrowing already. Astrostole
f017234: a trumpet whelk (Charonia lampas capax) has
just pinned down an eleven-armed prickly star with its siphon (Coscinasterias
calamari), and is now going to place its large foot onto the caught
arm. The victim has already lost one arm, which has started to regrow.
This story had a happy ending because the uneven topology of the oyster
bed, allowed the star to escape. The star shape enabled the victim to run
faster on this rough terrain, than the whelk could with its heavy shell.
[series of several images]
A trumpet whelk devours one starfish arm in a very short
time, and entirely. Perhaps it needs the calcium to build its heavy shell
with. In our aquariums we observed an eleven-armed star being eaten, one
arm at a time until only one arm remained, and this was eaten too.
f000927: seven-armed stars have a wide variety of colours,
from deep purple through grey to brown. They occur from the very north
to the very south of New Zealand. Astrostole scabra