By Dr J Floor Anthoni,1997
The underwater environment is in many aspects
representative of an exposed rocky shore in north-eastern New Zealand.
Its marine habitats, habitat zoning and sea creatures are representative.
So what you learn here is knowledge that applies widely to NZ's hard shores,
knowledge that makes your visit, snorkelling and diving, just so much more
enjoyable. But the Goat Island marine reserve, located between the edge
of the Hauraki Gulf and a long beach, with a sheltering island jutting
some 600 metres out in sea, is also a very special
place, discussed in its own chapter.
introduction: What makes Goat Island
such a special place? Wave regime, currents, diversity of substrate and
habitats: Wherever the conditions for life
change, the opportunities for the living organisms change as well.
bladder weed zone: The shallow seaweed
zone is dominated by tough bladder weeds. Sleeping here is hell but there's
a lot of food for grazers.
barren zone: Sea urchins and other grazers
keep a vast area of rock free from large algae.
kelp forest: The kelp forest is dominated by
the Stalked Kelp and it extends down to 18m deep
deep reef: The deep reef habitat is too
deep for the brown and green seaweeds. Fragile animals such as sponges
are found here. The sponge garden is a special case of the deep reef habitat.
sandy bottom: The sandy bottom is a rich feeding
ground for bottom-dwelling fish and those reef fish that forage here.
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Introduction Cape Rodney marks the outer edge of the Hauraki Gulf which is enclosed
by Little and Great Barrier Islands. It is fully exposed to N and NE winds.
The East Auckland Current bearing down from the North and making a wide
berth around Mokohinau Islands and Great Barrier, still makes its presence
known: the water is usually much clearer than inside the Gulf.
But having the mainland on one side, providing shelter for winds from
the NW to SE, makes the rocky shore here less exposed than that of outlying
islands such as the Mokohinau group. These factors together classify it
as a medium-exposed reef environment, which means that it is very
typical of the North Island's East Coast.
The presence of Goat Island brings shelter to some places, which
gives this coast a high diversity in species and sheltered places
to work and play. Not entirely by accident, is good access available right
where the island is. Geological studies have shown that a fault line has
twisted the earth around an axis running through the creek's valley, lifting
the Cape up by several metres and in the process perhaps causing Goat Island
to emerge from the sea as well. It thus happens that to the West the rocks
consist of layered sandstone whereas to the East they consist of the 'mother
rock', greywacke. Greywacke was formed from sediments, metamorphosed by
pressure and heat, such that its typical layering disappeared. Once situated
deep down, it was brought to the surface by tectonic movements. One can
never find fossils in them. But right above the greywacke one finds a layer
of mixed stones and sandstone, resembling concrete (right at the beach).
Here one can find big clams that about one million years ago, inhabited
these shores. One can also find the fossilised burrows of ancient heart
urchins that once crawled here through the sandy mud.
The two types of rock give rise to two different versions of the exposed
rocky shore. To the west, the coast is layered like pancakes. These layers
are clearly visible in the weathered cliffs but they extend equally out
into the sea, for several hundreds of metres. The soft rock can be burrowed
into by boring clams and the sand scours at them as well. These two forces
combined create undercuts and overhangs, giving shelter to small creatures
such as small fish (spotties and kelpfish) and crustaceans (small crayfish).
Waves run over these rock shelves, and while dissipating their energy,
make life hard for anything else but tough bladder kelps.
To the east, the rocks consist of hard Greywacke. These rocks tend to
crack vertically, giving rise to caves which are not found to the West.
The caves and long-lasting tumbled boulders provide good shelter for big
fish such as parore, red moki, silver drummer and marblefish and likewise
big crayfish. Waves bounce off the steep shore and are reflected back to
sea, failing to dissipate their energy. As a result, along this stretch
of coast, shelter is soon found in deeper water, reason for big fish such
as snapper to hang about on this side of the Reserve. Grazing sea urchins
are able to attach themselves firmly to the rock and to graze all plant
life down to a mere film of algae that functions as an underwater grassland.
All these conditions together, make Goat Island a very special place.
It is in fact so special that no similar place can be found within two
hours from Auckland. All the more reason to treat it with respect.
physical conditions responsible for the main habitats are wave action and
absorption of light with depth. As one goes deeper, wave action diminishes
rapidly, whereas light decreases more gradually. Furthermore, every habitat
is influenced by its inhabitants (grazers remove forest and extend the
'grassland'). As one moves behind a rock, one suddenly encounters shelter
or light may diminish suddenly. These factors give rise to miniature habitats
that may differ strikingly from the main habitats.
The diagram illustrates the typical zoning caused by wave action and
light absorption for a medium to highly exposed rocky shore.
f022912: habitat zoning around Shag Rock, during high
tide. Right on top a barren zone where seaweeds do not survive desiccation
during low tide. It is fringed by a narrow band of Xiphophora, then
a 2m band of bladder wrack (Carpophyllum maschalocarpum), and below
it the stalked kelp (Ecklonia radiata).
f001221: in the shelter of Goat Island, the zoning patterns
blur, and one finds seaweeds placed more or less by chance. However, where
wave action is dominant, the stronger bladder kelps prevail. Here the bladder
wrack grows higher up. Lower down one finds the more fragile featherweed,
and the stalked kelp.
A variety of bladder weeds grows in the shallows. Each has its
own tolerance to exposure. Most resilient is the wire weed (Carpophyllum
), followed by the bladder wrack (Carpophyllum maschalocarpum),
then the featherweed (Carpophyllum plumosum) and finally the flexible
weed (Carpophyllum flexuosum). The latter is mostly restricted to
very sheltered places such as inside harbours, since it can also tolerate
dirty water and low light conditions better. On the exposed cliff faces,
the flexible weed may be absent altogether and likewise the wire weed may
be absent from more sheltered places, or it may grow into bushy forms,
which look different.
On the barren rocks (urchin barrens) we find the main
shaver, the common (or green) sea urchin (Evechinus chloroticus).
Around it but often hidden in crevices, one finds limpets and chitons that
graze the surface very smooth. An important grazing snail which can keep
areas barren on its own is the Cook's turban shell
Lower down starts the kelp forest habitat of the stalked kelp
radiata). It descends down to about 18m where the light becomes insufficient
for plant growth, and slow growing sponges can compete for space. The depth
of the kelp's lower boundary is an indication of average water clarity:
the deeper this boundary, the clearer the water is. (Poor Knights 35m)
Ironically, on the East Coast, the sand bottom starts about where the
kelp forest ends, leaving very little area for the deep reef habitat of
sponges. Only around promontories where currents sweep the sediment away,
will enough depth be found for this habitat. Outlying islands such as the
Poor Knights and Mokohinau, have a deep sea bottom around them (80m) which
allows for a substantial increase in deep reef habitat. Both Goat Island
as well as Cape Rodney introduce small areas of deep reef.
The sponge garden habitat is a special case of the deep reef.
It occurs on flat rock shelves that may regularly become covered in sand.
Plants such as the stalked kelp can't germinate here but sponges can survive
periods of being smothered.
The shell trap habitat was not recognised at the time the reserve
was established and has been left out as a consequence. Where the rocky
shore meets the sandy beach, shells may get piled up during heavy storms,
providing a food binge for animals that can also survive the famine in
between binges (some snails and starfish). The shallow sand has also another
effect, that of scouring. During storms, all surfaces get sandblasted and
only some organisms can survive this. In the period of deadly plankton
blooms we observed that these heavily scoured areas survived better than
elsewhere, as if the sandblasting had an important cleansing effect as
well. Note that the deep reef around steep promontories experiences 'ground
swell', and receives a similar amount of sand scouring, also to its benefit.
In the El Nino years 1992-1993 New Zealand and particularly the area
around Leigh experienced dense and extensive plankton blooms. These were
so severe and lasted for so long that the entire kelp forest was killed
from Whangarei to Great Barrier Island to Kawau Island to Leigh. In the
following years of 1994-1995 plankton blooms kept knocking back whatever
recovered but by 1996 a sure and steady recovery was on its way. By the
end of 1997 many organisms had returned and it would require a trained
eye to see what was still missing, such as old specimens. But the plankton
bloom disaster has made huge changes to the zoning under water. As the
kelp forest became barren rock, sea urchins wandered off into the deep,
leaving their original zone insufficiently grazed. As a result, the kelp
forest rebounded here first, where the light is more favourable. In the
years following the event, no major storms were experienced to remove the
shallow stalked kelp. The situation now is that of hardly any barrens,
and extensive kelp forest. Eventually the original situation may return
but for the moment the habitat zoning maps of Goat Island are not at all
accurate anymore. In the summer of 2003, a similar kelp die-off occurred,
but not as severe.
Ironically, the reserve has not completely proceeded from bad to better
as one would have expected, although some species have benefited from being
left alone (red moki, kelpfish, marblefish, moray eel, conger eel, silver
drummer, crayfish), others (snapper, blue cod) benefited mainly because
people fed them. Some species have disappeared altogether (bearded mussel,
seahorse) while many species have visibly diminished in numbers (global
sponges, other sponges, sea squirts, stick bryozoa, hydroid trees, blue
maomao, demoiselle, kahawai, pipefish, prickly star, blue penguin).
In the twenty years of its existence, the reserve has not or hardly
been monitored. Some work has recently been done on commercial species
(snapper, blue cod, crayfish), with mixed results. The bottom line is that
very little has been learned from the concept of a no-take marine reserve.
The public, however, has learned to make good use of this magnificent
inheritance. In the seventies mainly used for spearfishing, the eighties
for research, the nineties have surrendered the reserve to the family.
In 1996 the visitor count stood at around 120,000 people per year. They
all came to do something that only twenty years ago would have seemed ridiculous,
that of watching (and feeding) wild fish. Discovering the diversity of
life, its elegant shapes and motions and that it is a lot more intelligent
than originally thought, gives people a real buzz. A new era has begun.
However, in 2001 the people who administer this reserve, decided to forbid
visitors to feed the fishes. As a result, the number of visitors has dropped
bladder weed zone The bladder kelp zone starts from low tide and ends at 3-6m, depending
on exposure. The dominant bladder kelp is the flapjack or bladderwrack
(Carpophyllum maschalocarpum), although on the very exposed side
of Goat Island, the sturdier wire weed (Carpophyllum angustifolium)
with its smaller leaves can be found. Click on the more
link for more information from our classification sections about the species
f028417: a lush stand of wire weed (Carpophyllum angustifolium)
is found on the most exposed places, where water runs up and down a sloping
f000718: a parore in olive coloured skin, strips lush red
algae off the rich forest of flapjack (Carpophyllum maschalocarpum).
f001227: full view of a parore (Girella tricuspidata)
as it swims by. This one wears its pin-striped business suit, which is
one of its most common outfits. They can change their colours to white,
black, olive, pin stripe and blotched (pyjamas). more.
f001227: portrait of a young parore, still in its yellowy
colours. Parore always seem to smile. Notice its fused teeth, which are
ideal for nipping and stripping seaweeds.
f000932: a group of parore feeding on sheltered flapjack
kelp. They often do so in the spawning season, in groups, seemingly having
delight in flaunting their elegantly moving bodies.
f007721: a large silver drummer (Kyphosus sydneyanus)
has left its group of 35 mates for a closer look at the photographer. These
fish are shy, and meeting a large group of big ones like this, is a rare
event. They feed in a simlar way to parore, preferring areas with strong
wave action. more.
f016906: a marblefish (Aplodactylus arctidens) rests
on a shelf off Pempheris Point. These fish are very shy, and even after
25 years of protection, do no fully trust divers. Marblefish graze the
shallows above the bladder kelp zone.
f030230: the kelpfish (Chironemus marmoratus) is excellently
equipped to hold on to its surroundings in fast currents. Its breast fins
have five hard fingers and its belly from lower lip to half-way, is rubbery.
These fish eat crustaceans, limpets and chitons.
barren zone (urchin barrens) Between the shallow bladder kelp zone and the kelp forest, usually
extends a barren zone, also known as sea urchin habitat, urchin
urchin flats, urchin barrens or grazed flats.
Ironically, it can also exist without any urchins at all. In some places
inside the Hauraki Gulf the barren zone is grazed by paua (Haliotis
iris) or Cooks turban shell (Cookia sulcata), in the absence
of sea urchins. On some very exposed places, where sea urchins cannot attach
themselves sufficiently, the barren area is still present, inhabited by
bushy forms of the pink paint (Lithothamnion sp.) and coralline
algae (Corallina sp.)
My own observations and measurements of this zone in relation to wave action,
have confirmed that the zone is created by large storms, which destroy
the stalked kelp in shallow water. After such an event, sea urchins may
or may not take over to maintain this barren strip and to widen it.
Once the main seaweeds are kept out by the forest-clearing sea urchins,
other grazers move in to graze where urchin teeth can't reach. Because
this zone is found in shallow depths from 3 to 10m, the sunlight is still
bright enough for plants to grow. Instead of large seaweeds (macroalgae),
the hairy and single-celled seaweeds (microalgae) grow much faster,
rendering the barren zone unintuitively productive. Camouflaged by their
coverings of pink paint, several species of snail, limpet and chiton are
found here. On these feed others.
f013229: urchins attacking stalked kelp. Once the kelp starts
bleeding, other urchins are attracted by smell.
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.
f001319: this picture shows many of the grazers of the barren
zone. The sea urchins are hiding underneath the ledge, only to come out
by night. The top of this shelf contains some bushy pink turf, grazed by
two Cooks turban shells. On the pink flats one sees cats eye and top shells,
and also radiate limpets. Most others are invisible. Inside the bushy pink
turf, lives a rich community of sea slaters.
f001932: near Waterfall Reef, the landscape is indeed
barren from below the cliff face at 6m depth to the sand at 15m depth.
In this photo the sea urchins are seen clustering together on the sheltered
side of a rocky outcrop. Clustering reduces the drag of the water, and
protects them from predation. But the leatherjacket hanging above them,
nips bits off their spines and tubefeet.
f00090: leatherjackets (Parika scaber) are versatile
niche feeders. We like to call them junk food eaters, because they
nip a little from many kinds of poisonous animals, like sponges. In this
manner they harvest only a little bit from a lot of creatures, so that
it seems as if they have no harmful effect on their environment.
f001013: spotties like this male (Notolabrus celidotus),
are common in the barren zone, but like leatherjackets, they too are universal
feeders, found in all habitats.
f001615: the seven-armed star (Astrostole scabra)
is capable of attacking and overwhelming sea urchins. Its extended stomach
is large enough to engulf the urchin, and to digest it outside its body.
Urchins, however, put up a good fight, stinging the star with their pedicellaria,
a kind of tube feet with claws.
f000927: Seven-armed stars come in a variety of colours,
from dark brown to grey, light brown to purple.
f019936: a red moki (Cheilodactylus spectabilis) puts
its big lips around bushy outgrowths of pink turf to suck their inhabitants
out. It does so with a loud sound. The ingested sand is then spilled out
through the gill openings, and sea slaters retained.
f020916: a bushy form of the pink paint (Lithothamnion
sp.) is found on steep cliffs underneath the bladder kelp zone in exposed
water where urchins cannot cling to the rock face.
f007701: snappers visit the barren zone to feed on a variety
of items, like sea urchins. Their presence reduces the numbers of sea urchins,
allowing the kelps to gain ground.
f022901: a diver gently strokes an orange nipple sponge (Polymastia
granulosa), showing that it can retract its nipples, even though it
has no muscles. Such large sponges were once common, adding a colourful
note to the environment. It is fascinating to consider that this sponge
must be able to fend off fouling algae. Perhaps it excretes a kind of weed
kelp forest Wherever one dives around the New Zealand coast, the kelp forest is
a major feature, found from the very north to the very south. The stalked
kelp indeed has adapted to the entire temperature range of over 6ºC
form north to south and over 6 degrees from winter to summer. It
is surprising that this large source of food does not have an accompanying
large number of grazers. The leaves of the kelp are slightly bitter but
not unpleasant to chew on. The kelp's most obvious herbivore is the butterfish,
but other grazers eat it too: marblefish, parore, silver drummer. Even
semi-pelagics like blue maomao eat it in times of shortage of zoo plankton.
The kelp's most voracious grazers are perhaps the almost invisible snails
living in their canopies, and the many swimming and crawling crustaceans
living there or visiting it by night. The deep kelp, which grows the most
slowly because of low light levels, appears also the least attractive to
grazers. It is not known why.
f014826: young stalked kelp, having settled inside the urchin
habitat, is attacked and eaten. Urchins do so in concerted effort, many
hands making work light.
f014826: by standing upright in the deep kelp forest, a diver
shows just how tall it grows. This is a healthy forest with a closed canopy,
underneath which, it is dark. These plants are all exactly the same age,
since the forest was destroyed in 1993 through lack of sunlight.
f016803: after a long period of dense plankton blooms in
Nov-Dec 92, the entire kelp forest died from lack of light. The dead plants
stood for a few weeks, while nobody noticed their discoloration. Then on
3 Jan 1993, cyclone Ola ripped their dead crowns off. They were pulverised
like wet toilet paper, never to be found. It took over 4 years to recover.
f017907: large storms rip kelp plants from places where they
cannot hold themselves strongly enough. Plants can get washed up on a beach,
and die as food for sand hoppers and slaters, but most remain in hollows
of the sea bottom, rolling like large live sausages. This tumble kelp
stays alive because it gets everything it needs from the sea water: CO2,
nutrients, moisture and light.
f014808: The vast stands of stalked kelp appear to have no
grazers, but these round bite holes, caused by butter fish (Odax pullus),
can often be found. Butterfish bite a hole in the middle of a leaf, by
sucking the leaf between their teeth, and biting a half-round cut-out.
In this manner, the strength of the leaf is not affected too much.
f007732: a large male butterfish gives the photographer but
one fleeting moment to take a picture. These fish are cunning and shy,
targets of spearfishermen for many years. Butterfish live peacefully in
harems dominated by a single male. They are also called greenbone for the
green colour of their bones.
f001921: it is quite safe underneath the kelp canopy. Here
and there one finds highways, frequented by many fish. Here a banded wrasse
(Notolabrus fucicola) stands still, surprised by the photographer
blocking his path.
f007101: Leatherjackets are found in all habitats, but because
they are slow swimmers, prefer the calm places such as the deep reef, and
underneath the kelp forest. This is a female leatherjacket.
f019916: the red rock crab (Plagusia capensis) is
mainly a plant eater. It is found in most habitats, from tide pools down
to the deep reef.
deep reef At the lower boundary of the kelp forest, the deep reef begins. It
is amazing to see how precise this boundary is, although the kelp forest
opens its canopy already a little higher up from this boundary, while some
sponges are found there too. For ecologists, this lower kelp boundary is
a good indication of the average clarity of the water. Not surprisingly,
they find this boundary creeping up, as waters become more turbid. It is
important not to look at the old plants, often 15 years of age, but the
young ones. In many places, these are found many metres higher up than
the lowest old plants, which is an indication of rapid degradation in recent
f004811: this photo shows a variety of sponges of the deep
reef in the reserve. Top left the crater sponge (Stelletta crater);
underneath it a fluffy ball of a deadman's finger soft coral (Alcyonaria
sp.), the yellow nipple sponge (Polymastia croceus), red meatball
sponges (Aaptos aaptos). Poking out of the sand the spikes of fakir
bed sponges (Ciocalypta polymastia) and (Polymastia agglutinans).
Orange carpet sponges (Crella sp.) are covering some parts of the
f004812: looking back to the previous situation, from behind
the large finger sponge in the background of the picture on left. The orange
fingersponge (Raspailia topsenti), underneath two meatball sponges
(Aaptos aaptos) and in the background the sponges mentioned in the
left-hand photo. A young blue cod swims behind the orange finger sponge.
f017101: where sand occasionally covers rocky platforms,
sponges can survive where no other organisms can. The sand here consists
of flakes of broken shell. In the centre the orange finger sponge (Raspailia
topsenti). At its foot a piece of boring sponge, flanked by a yellow
nipple sponge (Polymastia croceus). In the foreground and to the
left of the orange fingersponge, a dagger sponge (Axinella sp.).
The large yellow boring sponge on left (Cliona cellata) not only
carpets the rock, but drills holes in it as well. In this manner it survives
sand blasting, which happens here during large storms.
f000125: Orange finger sponges and yellow nipple sponges
on a deep reef outcrop. The fish in the background are blue maomao (Scorpis
f017104: diver and thin finger sponge (Callyspongia ramosa),
growing where once the kelp ended. This sponge came back faster than the
kelp, which is still absent from this pinnacle. (April 1998) The thin finger
sponge is rather variable in colour, ranging from dirty yellow to light
orange and from pink to light purple.
Floor Anthoni shows a deceased thin finger sponge at almost
the same place as the photo on left. In January 1993, all these sponges
died, including the once orange two-finger sponge (Paraphoxya pulcra)
in the right foreground. [Photo Dietmar Polster]
f028304: on the sand, and wherever a hole can be dug, the
sand octopus (Octopus gibsii) can be found. Since it changes its
surroundings like a builder does, it is easy to find. The sand octopus
is brownish white with an orange skin around its suckers. It eats mainly
shellfish, which it brings home to break open, hence the many shells around
its home. Note that it can change its colour substantially!
f006102: large crayfish are found in the deeper regions of
the coast. Here a large one has been tagged with an acoustic pinger, to
study how it roams about. The study proved that crayfish do move onto the
sand to feed, and back to their shelters. They also migrate seasonally
back to shallower water. Should this crayfish moult, it would leave its
pinger behind on its old shell. Since large crays moult less frequently
than young ones, researchers preferred them for their study.
sandy bottom When the marine reserve was staked out, it was thought that the rocky
shore, the reef habitats, were the ones needing protection. As a result,
the marine reserve now hugs the shore in a ribbon shape of 800m wide. But
a large area of the sandy bottom is sought for feeding, not only by a variety
of bottom dwelling fishes but also by reef dwelling organisms like crayfish
and porae. Thus many protected animals need to go outside the marine reserve
for their daily and seasonal needs. The marine reserve is just too small
to be sustainable for wandering species.
The sand represents a strange habitat in which it is easy to disappear.
Both prey and predator species do this. Whereas the reef habitat is capricious,
changing shape every five metres or so, the sandy bottom is boringly monotonous,
extending for huge distances without any change, it seems. Yet here too,
are habitat zones, depending on depth and exposure. Very little is known
f006036: a loose family of goatfish (Upeneichthys lineatus)
found resting on the sandy bottom. The large one is a spawning male and
the one in the foreground a future rival. All the others are females. Each
goatfish is born female. The three pale ones in front are last year's recruits,
the kiddies. Note how the three mature females take positions close to
the spawning male.
f004715: A spawning male goatfish resting on a yellow boring
sponge. Goatfish can change their colours in seconds. It took nearly 30
minutes to take this photo, as the fish went pale white, each time the
photographer sneaked a little closer. Goatfish used to be found in schools
of hundreds in the Goat Island Channel, but they disappeared in the early
90s. A few can still be found. in deeper water
f000821: a mature male blue cod (Parapercis colias)
has taken possession of an area of flat sand. In the background a small
female. The blue cod around the North Island do not grow as large as those
around the South Island.
f017911: the smaller blue cod are all female, shown by their
brownish coloration. Blue cod do not belong to the family of cods, but
the family of weavers.
f002610: since blue cod do not have swim bladders, they sink
to the bottom. Not having a swim bladder allows them to make fast excursions
to the surface in their raids on prey. But sitting on the bottom has its
problems, like sitting in swirling sand, capable of clogging one's gills.
for this reason, these fish often skip breathing like divers do. Now and
then, however, they need to catch up with a wide yawn.
f002613: in the final stage of its yawn, the blue cod shows
all of its teeth and gill rakers, which are studded with teeth too. Prey
is caught and gulped inside its cavernous mouth; then ground to bits with
its toothed gill rakers. Notice how it has expanded all its gills too.
f002311: an eagle ray (Myliobatis tenuicaudatus) is
resting on the sand in the Goat Island Channel. Notice its head, shoulders,
whip tail and little fin. When very young, they have a yellowish to olive
colour with blue spots.
f005814: this eagle ray has taken a wary pose by lifting
its body partly out of the sand, ready for taking off. Like an air plane,
an eagle ray can fly through the water only when water flows both over
and under its wings. This is the reason why air planes stand high on their
landing gear. Standing high on its landing gear, this ray only needs to
lift its wing tips, to become water-borne.
f021005: eagle rays are very gracious swimmers. Notice how
this one flies over the sand without even stirring it - a difficult example
for divers to follow.
f021002: closeup of a resting eagle ray. Notice its steep
f002312: Within the marine reserve, the eagle ray's main
food source is the sturdy Cooks turban shell (Cookia sulcata). It
finds these by smell, often folding its wings double to shuffle inside
the narrow gaps between the stalks of the kelp forest. The shell is taken
to a pebbly spot, where it is crunched with a loud crack. This photo shows
the pearly remains of the cracked shell.
f002215: a short-tailed stingray (Dasyatis brevicaudata)
has carefully burrowed herself in the sand. This female is highly pregnant,
and will give birth to two fully developed babies, which immediately fend
for their own. Amazingly, this 'primitive' cartilageous fish has evolved
a method of internal fertilisation and live birth. Some sharks also give
birth this way.
f004623: A large porae (Nemadactylus douglasii) stands
head-down, digging for food in the sand, while a young snapper carefully
watches for spilled morsels. Porae suck up large mouthfuls of sand, in
search of hidden worms and sand slaters. They expel the sieved sand from
their gills. Porae need clean sand, which unfortunately, is gradually being
polluted by mud.
f028310: a sand octopus (Octopus gibbsi) has left
its den to forage on the sand. These animals have developed a sense of
taste on all of their arms, with which they routinely inspect the environment.
The sand octopus feeds mainly on clams. They can smell shells burrowed
finger-deep, digging these up by blowing the sand away with their jet pipe.