Goat Island's marine environment - special cases
By Dr J Floor Anthoni, 1997
For the keen visitors to the Goat Island Marine
Reserve, this page describes some interesting aspects of its marine environment.
Although the area is somewhat representative of a north-facing exposed
coastal shore in northern New Zealand, there are enough special cases that
make it an exceptional place and not at all representative. What happens
at Goat Island can thus not be extrapolated to more 'ordinary' shores. At the end of this chapter is a unique biogeography
that gives more insight in the ecology of this marine reserve.
sponge garden: Where sand covers deep
rock platforms, a community of sponges can out-compete the stalked kelp.
It is a fragile world.
intertidal: The intertidal area of the
marine reserve is steep and inaccessible on the eastern half of the coast,
but wide rocky platforms are within easy reach on the western half.
shell trap: Shells washed up on Pakiri
beach and transported by waves and currents, get trapped in the first foothills
of the rocky shore. This area lies just outside the marine reserve.
mussel bank: A natural mussel bank with
its fascinating community has been left unprotected, outside the marine
reserve. Whether it will survive, is questionable.
promontories: Promontories, jutting
out in the current are where many pelagic fish congregate.
shelter: The shelter provided by Goat Island
is a unique feature of this marine reserve, apparent from a number of exceptional
caves: Around Goat Island several kinds of
cave are found. Some are barren, some not.
night shift: During the night, most of the
creatures seen by day, sleep and hide. The sea becomes empty and the night
shift takes over.
visitors: The marine reserve has its visitors,
usually migrating fish from elsewhere. They may take up residence for a
while, then disappear again. Boarfish, large snappers, tarakihi,
miscellaneous: Miscellaneous interesting
facts and habitats. The hopping kelp;
biogeography: A different way of looking
at the marine reserve, is obtained by identifying the main influences on
the marine habitats in relation to where they occur. It is called biogeography.
The marine reserve varies considerably when traversing it from east to
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sponge garden West of Goat Island, the coastal rocks consist of mudstone. This kind
of rock is layered and forms platforms in the sea, often undercut, creating
hiding places for many creatures. These rocky platforms are not found to
the east of the island. The deep sediment flats are periodically covered
with sand, which is unfavourable for the establishment of the stalked kelp.
However, sponges are able to survive while covered with sand, and they
eventually grow large enough to protrude above the sand. In this manner,
sponge gardens are formed with a wide variety of sponges.
Because these sponges cannot be distinguished on depth sounders or fish
finders, seamen consider these places safe for anchoring. Attached to the
anchor, is a long chain, partly lying on the bottom, partly leading up
to the boat. As the tidal current changes, the whole chain is moved to
the opposite side, dragging over the sponge garden, and uprooting all sponges
in its path. For this reason, the sponge habitat should not be anchored
on. Unfortunately, the Department of Conservation has not spent any money
on improving the reserve's infrastructure, and has not provided suitable
boat moorings. It has not even maintained the system of marker buoys, which
was present in the beginning.
f000124: sponges on sediment flats are sensitive to damage
from anchor chains.
f017101: standing on firm rock but surrounded by shelly sand,
these sponges thrive where plants cannot.
intertidal Three rocky platforms are located in the intertidal zone: Hormosira
Flats to the right of the beach, Echinoderm Flats to the left,
and Okakari Flats at the western boundary by Okakari Point.
It is not known why each has a different level, Okakari Flats being
highest and Echinoderm Flats lowest. Okakari Flats is too
high to be interesting, and is difficult to reach.
Hormosira Flats has the deepest rockpools, some too deep to be studied
by students. An outlet of the Laboratory's seawater system ends in one
of the rock pools, which makes it perhaps the only rockpool in NZ, with
flowing water. This pool is also richest in diversity. Hormosira Flats
is accessible for a long period in between high tides, which makes it an
excellent study area.
Most interesting, though, is the lower Echinoderm Flats. Only
for about one hour around the low tide, can it be visited. This area has
many very shallow rock pools, and many stones and boulders housing a great
variety of creatures. When you intend to visit these intertidal platforms,
go bare-foot, because your shoes cause damage to the marine life that clings
to the shore everywhere. Just take care not to cut or stub your soft feet.
Make sure you've carefully replaced all stones you turned. It is a most
A separate chapter will be devoted to the ecology of these two intertidal
shell trap Where the rocky shore meets a large beach, the environment is
not something in between the two, but it is unexpectedly different. The
beach is characterised by fast moving sand, in which only fast burrowing
surf clams such as tuatua (Paphies subtriangulata) can maintain
themselves. Deeper down, burrowed in more stable sand, one may encounter
the fan shell or horse mussel (Atrina pectinata zelandica), and
the occasional scallop (Pecten novaezelandiae). No creature, living
in or on the sand, while moving only slowly, can escape the brute forces
of large storms (See Oceanography/waves).
Large waves, which we call swell, rise over the shallows, from about 40m
depth. Here they move the water to and fro over the bottom, brushing the
sand faster towards the beach than away from it. In the process, burrowing
clams, snails and starfish are swept towards the beach from vast distances
in sea. It can lead to massive shell wash-ups as shown in the photographs
below. Miraculously, such wanton waste disappears within a few days after
the storm. Where do all those shells go to?
Most become buried by the sand as it resettles after the storm, but
a good number travel along the beach, repeatedly washing up on the beach,
and off it again, until eventually there is nowhere to go but the peaceful
gullies of the reef habitat. Here a massive amount of food collects once
or twice a year, giving a livelihood to a community of frugal organisms
that are capable of living from binge to famine. When the food is plentiful,
they overeat themselves, while growing quickly. In the lean times in between,
they borrow from their bodies, being able to shrink accordingly.
Not all the shells washed up on the beach die. Some end up in the deeper
sand of the shell trap habitat, forming dense beds, on which the adaptable
octopus feeds. This remarkable habitat lies outside the marine reserve,
and is not protected.
f950728: On 23 April 1995 the beach south of Te Arai Point
(West of Goat Island) was covered in young horse mussels, at places 0.6m
thick., estimated at 4000m3, or 400 tonnes of meat. Within days, the beach
was clean as if nothing had happened.
f950726: the bulk of the shells consisted of young (2 year
old) fan shells or horse mussels (Atrina pectinata zelandica). Most
of these were dead, and altogether there was too much food for the traditional
scavengers, the sea gulls.
f001210: horse mussel shells and other debris washed into
gullies of the rocky shore reef habitat. Live shells re-established themselves
in the sand at the foot of the rocky shore.
f003708: the sand octopus (Octopus gibbsi) is not
capable of living without food for a long time, but it is capable of unbelievable
growth when plenty of food is available. It is very versatile in finding
new kinds of food, which keeps it alive in averse conditions, when it grows
f003710: sea dahlias (Isocradactis magna) are rare
on the East Coast, but in the shelltrap habitat they grow large and colourful.
Having large mouths, and consisting entirely of stomach, they can swallow
and digest large prey, such as complete shells. What cannot be digested,
they expel through their mouths again. In the lean times, these anemones
do not need to shrink (which they can), because they can live from symbiotic
algae inside their skins, that convert sunlight to food.
f001103: a small eleven-armed prickly star (Coscinasterias
calamaria) searches for food amongst the washed-up shells. With smell
sensors at the tips of its arms, it can navigate precisely to any source
of food, arriving there before others. It then extends its stomach over
its prey, to digest it outside its body. The stomach juices are digested
further inside its body. These stars are versatile feeders, having many
tricks to catch their food. In the lean times, they can last for many months
without food, shrinking their bodies as required.
Reader please note that the shell trap habitat has been
named by myself, and has not (yet) been recognised as such scientifically.
mussel bank Natural mussel banks of green-lipped mussels (Perna canaliculus)
have disappeared from wherever they once were on the East Coast, partly
because people overharvested them, but perhaps mainly because mussel spat
(their larvae) do not want to settle on mud-covered rock. On the shallow
rock platforms that are the last rocky outcrops before the long Pakiri
Beach, a natural mussel bed has survived. Why?
These shallow rock flats are brushed with sand most of the time, a kind
of sand blasting which keeps them free from mud and planktonic sediments.
Once in a while (every 10 years), mussel spat reaches this site (from the
older animals already there?), and settles only here - not 50m west, nor
east. After 2-3 years of growth, the local people gradually start to harvest
the mussels, which leads to a complete wipe-out after only a couple of
years. In the 80s, the mussel bank was poorly known, and people harvested
only the intertidal rocks on low tide. After 10 years, mussels reached
18cm in size. However, in the 90s, the submerged rocks became popular,
to the extent that this natural mussel bed may not survive. It is located
just outside the marine reserve, and is not protected. As I write this,
in December 2002, not a single mussel can be found on the mussel bed. Nobody
had the foresight to leave a few for breeding.
f003711: a clump of old greenlipped mussels stands isolated
on a sand-polished rocky platform. These were spared because they were
considered too tough to eat. (Nov 95)
f003712: The natural mussel bank is now and then submerged
promontories Promontories are rocky headlands, jutting out into the sea. Because
of their shape, they alter the marine environment in various ways. They
distort the tide wave which fills and empties sea basins, resulting in
strong currents, benefiting many marine species. They usually have one
exposed side, while providing shelter on the other side, which is favoured
by many marine organisms.
The combination of currents and exposure by waves, causes the sand to be
deeply dug out, providing attachment for sponges. It can thus be
said that promontories promote biodiversity, and are thus worth protecting
by marine reserves. However, the Goat Island marine reserve stops at the
promontory of Cape Rodney. Here fishermen congregate and place their cray
pots, with the sole intention of taking fish from the marine reserve, by
luring them. Because fish do not know where the boundary is, this results
in an unstoppable drain of life from the marine reserve.
f000623: a group of blue maomao lazes about in the open,
waiting for the tide to turn, and for their mates to finish being cleaned
f001225: detail of a blue maomao (Scorpis violaceus),
while swimming by. These fish normally live along the outside of Goat Island,
where the main current runs. But they are attracted to the beach because
people feed them there. Blue maomao are semi-pelagic fish, obtaining their
food from the zoo plankton, but needing the shelter of the rock face for
Blue maomao cannot tolerate murky waters, reason why
they are found mainly around outer islands.
f002512: The grey maomao (or sweep) (Scorpis lineolatus),
looks very much like the blue maomao, but is smaller and shorter. It tolerates
dirty water better, and is now gradually replacing the disappearing blue
f001017: closeup of a young trevally (Pseudocaranx dentex).
When young, these fish live in small schools, often fossicking in the reef
habitats and on the sand. Later they will assemble into large pelagic schools,
feeding on zoo plankton, often far away from the shore. However, some remain
close to shore all their lives.
f022804: Butterfly perch used to be a common fish in the
marine reserve, but it is now restricted to the clean currents, such as
near Cape Rodney. Here they are seen grouped behind a rock face, just outside
the current. By night they sleep in shallow depressions of the rock face.
The one in the foreground-right, has the facial makeup of a spawning male.
f017130: detail of a butterfly perch, (Caesioperca lepidoptera).
the shelter of Goat Island The presence of an island close to the shore, brings shelter to a large
area. Goat Island's shape has been honed by many centuries of sea erosion
to what it is now, providing shelter to a relatively large area for its
small size. Fish frequent such areas, and where fish congregate, they unknowingly
pass the message of safety to each other. Fish attract other fish. Not
surprisingly, both density and variety of species is high in the shelter
of the island.
Like the fishes, divers and snorkellers also benefit from the shelter of
Goat Island. It makes the place accessible for more days of the year, and
it provides for more comfortable snorkelling and safer swimming. But shelter
also changes the environment, making things happen that do not (or in a
lesser way) happen elsewhere.
f001818: in the deeper parts of the Goat Island Channel,
sheltered from the worst of storms, one can find forests of the fragile
featherweed (Carpophyllum plumosum), an enchanted forest.
f002226: in the shelter of Goat Island, one can marvel the
capriciousness of shallow stands of stalked kelp (Ecklonia radiata),
which would otherwise grow 10m deeper. The play of light in this shallow
seaweed forest is a spectacle to behold.
f001811: on calm days, a great variety and quantity of fish
assemble in calm sea gardens, as shown on this picture (and well away from
the beach!). Some do 'fish watching', others laze or play. Everywhere cleanerfish
attend to the sores of others. In the foreground a male spotty and
a parore. In the distance on right, one year old snappers. On left a school
of young trevally. Many other fish are hidden or difficult to see. Click
on this image for a larger one, because these
glorious moments are becoming rare. Notice the variety of seaweeds.
f007727: five silver drummers (Kyphosus sydneyanus)
hang motionless in an orderly formation awaiting the services of a young
trevally (Pseudocaranx dentex) cleanerfish. The drummers belong
to a group of over thirty, all of similar age, and they know each other
well. A kind of pecking order has been established in the over forty years
they have been together. Fish make good use of body language to communicate
with their own species and in between species. <continued below>
At this very moment, trust is established between
the large drummer and the tiny trevally, by the large fish offering its
weakest and most sensitive part, its eyes. It faces the cleanerfish with
its head high, denoting its turn in the queue. By contrast, all the others
bear their heads down, as if saying that they are not part of the game.
The top fish has changed some of its fins to pale white, but three others
are still in 'pyjamas', saying that they are out of the game. The one in
the distance left, has turned pale, saying that is next in line, but it
is still facing down and away from the cleanerfish. In this manner, the
cleanerfish is not distracted, and will pay all attention to only one drummer.
The top drummer will now tilt its body and wave its breast fins, to indicate
where the itching spot is, but the cleanerfish has good eyes for these
matters. It will go around the drummer, picking sea lice off its skin,
until it is satisfied and swims away. Fish like these large silver drummers,
can spend a lot of time socialising this way. Watching how fishes behave,
is time-consuming, but most satisfying. It requires places where people
behave with restraint. If you want to see events like this, don't come
on holidays or in the weekends.
f002809: a large snapper ('Mr Perfect') is accompanied by
a young trevally. The trevally removes sea lice from beneath the snapper's
scales, while the snapper provides protection to the cleanerfish. At night
they sleep together, the cleanerfish often under the snapper's arm pit.
These relationships do not last forever, since other snappers vie for such
privileges, and trevallies eventually grow up and swim away.
f021026: a school of jack mackerels (Trachurus novaezelandiae)
has come to the sheltered shallows for resting and digesting. They had
great interest in the photographer, who took this photo and most on this
page, while snorkelling. Fish seem to be little disturbed by a freediver's
need to go back up each time. By contrast, a diver's bubbles always make
f001820: after their breakfast, a group of parore (Girella
tricuspidata) is speeding home to their communal sleeping den. Here
they will spend more time socialising, digesting and resting. Later they
will go out again for lunch and dinner. Shelter is very important in the
lives of parore. It appears that many fish return not only to shelter,
but also to warmer water, which helps to speed digestion, and perhaps creates
a feeling of wellbeing because of this. (remember your last big meal?)
f002220: for parore, food is easy to obtain on account of
the large seaweed habitat in the marine reserve. Here they are resting
in a shallow, sheltered spot.
f007237: a group of juvenile broad squid (Sepioteuthis
australis) swimming over shallow, sheltered kelp. Broad squid live
in the deeper coastal waters, but visit the coast for laying their eggs.
They do so on a calm night.
f002313: a cluster of white egg capsules has been laid
by a number of females, during a moon-lit night. Each finger contains 3-4
eggs, safely encapsulated by tough skin. After a few weeks, one can see
little eyes, while the skin becomes more transparent too. Then the little
babies are born, smaller than the nail of your little finger, all ready
to go, flashing their skins and puffing ink as well! They assemble in little
schools, devising all the means they have to elude their many predators.
The white squid eggs were attached to
an uncommon brown seaweed, the
oak-leaf kelp (Landsburgia quercifolia)
f001833: schools of pipers or garfish (Hyporhamphus ihi)
can be found in the sheltered waters of the Goat Island Channel. Most people
fail to see them because they are looking down, rather than ahead, just
under the surface.
caves and crevices For many organisms, caves and crevices are important niche habitats.
For some it is an important shelter in their youths; for others a shelter
by day; and for many a shelter by night. Marine 'hot spots', the places
that show high numbers of fish on a depth sounder, are almost always near
an undersea cave. Wrecks provide artificial caves, and are therefore attractive
to many fish species. The Goat Island marine reserve is unusually rich
in caves, crevices and ledges, and has therefore always enjoyed a high
number and diversity of species, compared to other places, regardless of
its protective status.
f000919: crayfish (Jasus edwardsi) have packed themselves
as tight as sardines in a tin, for maximum defence. In this formation,
even a large octopus finds them difficult to handle.
f004625: a crayfish seeks solitude for the delicate process
of moulting - shedding its old skin and hardening a new skin. If it does
so in the colony, it will be canibalised by the others.
f010720: safety in numbers is the motto of these crayfish
inhabiting a crayfish city of which there are only few inside the reserve.
Protected by the large males in front, the smaller females and young ones,
stay in the back.
Before the females moult, they select a free male, whose
size is important to them. After moulting, the male deposits a packet of
sperm on their sternum (chest), which the females use when ready
laying eggs between their swimmerets (pleopods).
f010725: females holding on to the backs of the males of
f003505: a crayfish moult (its old skin) looks very much
like an animal that has died. On closer inspection, the skin is entirely
empty. The animal has pulled itself out of its antennas, legs, eyes and
even its delicately branched gills! First it stops eating for one or two
weeks. Then it shrinks its body, while secreting a lubricant between its
old and its new skin. Then suddenly, within a few minutes, it pulls its
chest out of the front part, and its tail out of the rear part.
f214312: a female spanish lobster (?) crawls out of her old
skin. At the very moment this photo was taken, she shook her tail part
off in a single flick. Notice how fresh her new skin looks. At this moment,
the smells produced by the moulting, will attract predators, like conger
eel, crayfish and large hermit crabs. Against these, her soft skin offers
no defence. To avoid this, she'll wait quietly in a crevice of the reef
until her mandibles are hard enough to eat with. For her, the availability
of a narrow crevice, is of utmost importance.
f018734: a dwarf scorpionfish (Scorpaena papillosus)
lives almost entirely in the confines of crevices, unlike its large cousin,
the 'granddaddy hapuka' or northern scorpionfish (Scorpaena cardinalis),
who lies in ambush in the open, by day and night. The northern scorpionfish
has disappeared from the Goat Island marine reserve, perhaps because it
cannot tolerate murky water as well as the dwarf scorpionfish.
f213101: the dwarf scorpionfish can be identified by its
row of four spines on a bony plate under its eye, followed by two spines
on its gill cover. It also has a different face, with wide-set eyes.
f006305: for the fishes of the night shift, caves and crevices
are very important for shelter by day. This photo shows a young bigeye
(Pempheris adspersa), waiting for day to turn into night. Bigeyes
are, like other fishes, born in the open plankton. At the size of about
2cm, they settle down to the reef, but they have not become nocturnal yet.
After about one year, hanging out in clear daylight, they start to behave
like the adults do.
f016915: caves are critical to the lives of red moki (Cheilodactylus
spectabilis). They sleep there by night. Because red moki are faithful
to their caves, they do not wander out of the marine reserve, thus enjoying
full protection, and their numbers have rebounded spectacularly. The photo
shows a 'moki hole' with some of its occupants. Some moki holes house 50-100
moki by night. To make an evening dive, waiting for them to arrive in small
groups at a time, is spectacular.
the night shift A night snorkeldive in the Goat Island Channel is an experience not
to be missed. Make sure you have adequate light. Choose a calm night and
clear water, and go in from the beach or a little further to the right.
Going in just after dark, is usually done, but a more satisfying night
dive begins later.
Prepare your night dive by making someone aware that you are in the water,
and when you will return. Better still, have someone wait for you on the
shore. Bring a gas lamp and place it on a prominent point, to navigate
by. You must be able to see it from where you are going to swim. Make sure
you are familiar with the place where you are going to dive. Bring a bright
waterproof light, such as used by divers and have some spare batteries,
just in case.
A night snorkeldive or SCUBA dive usually lasts shorter than a dive
by day, because of your time appointment. 45 minutes is about the norm.
Stay together, because it is often difficult to find one another again.
Enjoy what you see together.
For divers, a compass is not strictly necessary if you are prepared
to surface now and then. Reorientate yourself based on the gas light, and
other lights around. Be aware that many lights will be switched off some
time during the evening.
By night, lit by the narrow beam of your torch, the underwater environment
assumes a spooky appearance, which is much more colourful than by day.
This is because there is less blue light diluting the true colours. If
you can, make an effort to swim down, because this will enhance colours
appreciably. There are no animals to fear, but you may blunder into a jellyfish
if these are around. In the beam of your torch, some fish such as pipers,
may become disorientated and bump into you.
f012329: bigeyes (Pempheris adspersa) in a deep crevice,
waiting for the night to fall. As soon as it becomes dark, these little
fish come out of hiding, to swim in the open water in search of swimming
bristleworms, sea lice and others who also come out at night. Because their
bodies reflect the light so well, they are a prominent feature of any night
dive. It is not known whether these fish navigate back to their own crevices,
or whether they just seek the nearest dark shelter available.
f007316: almost equally common as the bigeye, the slender
roughy (Optivus elongatus), shares the same crevices with them,
and appears to hunt for the same kind of food. It is ecologically perplexing
how two similar organisms can peacefully share the same shelter and food
f009830: resting goatfish (Upeneichthys lineatus)
are stunningly beautiful by night, and a delight wherever they appear in
the diver's light beam. The two barbels, which are extensions of the mouth,
and very sensitive to smell, would allow them to dig for food even during
the night. However, they prefer to rest. Large congregations of goatfish
by day appear to vanish by night, and it is not precisely know where they
f019220: the southern conger eel (Conger verreauxi)
comes out only by night, when it hunts for food. It is not just a scavenger,
but an active predator and very efficient at that. Although its teeth are
negligible, its formidable jaw slams shut over its prey, instantly killing
or stunning it. With its very sensitive nostrils, it finds its prey, attacking
it without hesitation. Goatfish, cod, blue cod and others are on its menu.
The prey is often taken home to its cave, where it is 'shared' with brightly
f009820: most fish change their skin colours by night. Here
is a porae (Nemadactylus douglasii) in pyjamas. Compare it with
its day-time outfit, on right. Porae do not fossick by night, but rest
f004623: porae feeding by day.
f020128: during the night, the spiny lobster (Jasus edwardsi)
is out to fossick for food. Here one is seen at the moment it bumped into
a kelp stalk. Their eyesight being weak, they find their way almost entirely
by smell and feel. Yet, each time they are able to find their homes. Crayfish
are versatile in what they eat, from anemones, seasquirts to dead animals.
They can even catch triplefins.
[photo taken at the Poor Knights Islands]
f017330: a very cryptic crustacean is the killer prawn, also
called prawn killer (Ibaccus alticrenatus), both bad names for the
animal, because it does not behave like its name suggests, in aquarium
studies. It lives in sheltered places, and is very shy of light. It swims
in erratic jerks.
visitors Particularly our commercial fish species, migrate from place to place,
and may take up residence in the marine reserve for a while. This chapter
shows the more common ones.
f006019: a john dory (Zeus faber) waits in ambush
behind a rocky outcrop. These fish live normally in much deeper water where
they are caught commercially in trawl nets. These fish can change colour
to suit the occasion. Its extendable jaw and flexible body construction
allows it to swallow prey almost as large as itself!
f017712: john dory are very adaptive in their hunting strategies.
Here one is seen flat on its side, having changed its colour to green,
to make it resemble a stone. In the top right corner its prey, a wary school
of jack mackerels.
f002420: a young giant boarfish makes its inspection round
in the Goat Island Channel, where it is seen from time to time. People
ask "What is the snapper with a hollow long nose?". These fish normally
live in deep water, but may take residence for some time in much shallower
f006124: a group of young giant boarfish (Paristiopterus
elevatus), accompanied by one tarakihi (Nemadactylus macropterus),
hang-gliding in formation in the current rising above a reef ledge. The
tarakihi is totally confused about its identity, seeking the company of
fish that look about the same, silver with a dark collar.
f017920: meet Monkeyface, the legendary snapper of the reserve.
It is a very large fish, weighing in at around 15kg, and it is perhaps
40 years old. However, for its daily and seasonal needs it has to leave
the marine reserve, which is simply not large enough. Its survival therefore
does not depend on the protection we give it, but on its own cunning. It
has disappeared several times, once for three years!
f017106: not all creatures visiting the marine reserve are
migratory. At times, an influx of sessile plants or animals is seen. Here
is an uncommon yellow hydroid tree. To receive visitors from cleaner waters,
is good news. Those from murky waters may signal that the reserve is degrading.
miscellaneous The sea is a fascinating place, with many unbelievable creatures and
unexpected processes. In this section we'll collect a miscellany of them.
Since the Goat Island marine reserve is so easy to reach, many divers can
experience them at first hand.
The hopping kelp.
East of Goat Island, at the foot of the rocky shore,
extends an area of mixed sand and stones. Storms cannot move the
rocks, but they can move the sand around. However, the drag on the canopy
of the kelp is sufficient to move plants with their rocks attached. On
average they are moved towards the coast, and from other places towards
this area. In this manner, the cobbles are herded into this special habitat,
a process that takes thousands of years.
f004632: The photo
shows a young thin-finger sponge and in the background isolated stalked
kelp plants, each attached to a cobble-sized rock.
f032214: On right a kelp plant secured to a cobble, living
below the kelp's photic zone. Being moved by deep waves and currents, it
eventually ends up in a sheltered place.
The careful observer will notice that such hopping kelp gardens can exist
deeper than the photic zone, beyond which no kelp plants can live for lack
of light. The reason is that the white sand around, reflects the light
upward, thereby almost doubling the light available to the sparsely populated
biogeography It is unusual to find this chapter tucked in behind all others. It
should in fact have been at the very front, together with ecology and main
habitat zones, because it describes the reasons for some of the major differences
found inside the marine reserve, leading to a better understanding of what
lives where and why. What has been written here is entirely my own work,
based on my own observations. They are not (yet) backed by any scientific
research. I therefore welcome any discussion and research.
The habitat maps made by Dr Tony Ayling in the mid 1970s, described
the topology (seascape) and which main seaweeds grew there. In doing so,
it took into account the two major influences on the seascape: sunlight
and wave motion. These two factors oppose each other, leading to a surprising
variety of life. The deeper one goes, the less light and the poorer biological
productivity becomes, which is bad for life. However, at the same time,
the destructive action of the waves diminishes, which is good for life.
These factors are roughly the same over the entire width of the exposed
rocky shore inside the reserve, but may change suddenly over small distances,
depending on the shape and orientation of the reef. In all, the mapping
method used, has proved to be a very good way of describing a marine environment,
but it obscures some of the finer points.
In this chapter we'll examine the factors which are not constant all
along the shore, such as currents, wave movement, sand scouring, type of
substrate (rock/sand) and fouling by mud. The schematic map shown here
attempts to map these influences.
The map above shows an initial attempt at defining the biogeographical
regions of the marine reserve, dictated by the major environmental influences.
The map shows the coastline of the marine reserve with Goat Island near
the middle. As discussed before, the coast is high, the water deep (15-23m).
The rocks west of Goat Island consist of pancaked mudstone, resulting in
flat shelves. The rocks to the east consist of hard greywacke (a metamorphosed
sedimental rock), resulting in a steep coast with deep broken rock, and
caves. This coast suffers less wave friction because waves are reflected
back, whereas they break over the flats. The broken rocks have vertical
water movement as opposed to horizontal for the flats.
Before mud from land and coastal erosion became a major influence (since
about 1990), the main influences were those of tidal currents, sand movement
Oasis First and foremost, not shown on the above maps and other maps of the
marine reserve, is the 40km long beach to the west. It is a de-facto desert
for marine life that prefers a hard shore. For migrating fish it doesn't
provide shelter and a place to sleep or rest. So Goat Island is an oasis
at the end of this very long stretch of beach, an oasis that attracts migratory
fish from far afield, such as snapper. Thus Goat Island has always been
a 'snapper trap' attracting these fish from a large area around. When scientists
quote the success of marine reserves, based on snapper counts inside the
Goat Island marine reserve, they are either ignorant about the oasis effect,
or just dishonest.
Currents Currents run around Cape Rodney to the extent that diving there can
be hazardous during spring tides. They influence the seascape considerably,
bringing planktonic food for schools of planktivorous fish of several species,
and sessile filterfeeders like the luxuriant sponges of the deep reef habitat.
During storms, sand moves here too, gently scouring the sponges, and keeping
them clean from sediment and sticky algae. Here one finds the butterfly
perch, which has disappeared from the outside of Goat Island. However,
demoiselles have disappeared from here too.
Currents also push around Goat Island to become a notable influence
on the environment there. Schools of blue maomao and trevally are found
here, and again, a thriving deep reef community, although not as luxuriant
as around Cape Rodney.
Shelter The only notable shelter inside the reserve is found around Goat Island.
It starts already behind North Reef, and extends along the sides of the
island, all the way to the beach. This area is prime real estate for nearly
all species of fish, and a variety of fragile sessile organisms. It produces
abundance and variety.
Sand Sand is found over a vast area, starting at the foot of the reef. However,
where it does not move, it is of no relevance to the reef communities.
On the map we marked the areas where sand is on the move, covering rock
flats now and then (the sponge gardens NE of Goat Island), or where it
moves inside the Goat Island Channel, at times covering the edge of the
Moving sand is a normal feature of the Pakiri Beach, to the far west,
but it moves into the rocky areas, where the shelltrap and the mussel bank
are found. On these it has a major influence. But the scouring of sand
extends further into the marine reserve, causing abrasion and sponges thriving
in shallow water.
Mud Since about 1990, mud has become of major influence on nearly all habitats
inside the marine reserve. It arises mainly from the Pakiri River to the
west. In its water catchment area occurs some very steep farm land, with
high degrees of erosion and soil loss. During large rain storms, a massive
amount of mud enters the sea, and currents disperse it into the marine
Where indicated, the mud affects mainly the deeper areas where it settles
over the sand, suffocating shellfish beds. Because of this, the sand bottom
(and its inhabitants) has changed considerably in the past ten years. Nothing
is known about the seriousness and extent of this.
Mud also enters from the Whakatuwhenua Stream, depositing large quantities
in the shallow centre of the marine reserve. After years of farming and
initial removal of its natural forest cover, the coast bordering the reserve
is eroding badly. The unsustainable browsing of introduced possums, adds
to the problem. The spoils of slips are waiting for waves to be lifted
by a high tide, washing them out, and sending slicks of mud into the reserve.
Located so close to the shore, the mud disperses only slowly along the
steep coast, which is also sheltering the area from land winds. This mud
causes major damage in the areas indicated.
f013205: mud enters the reserve from the Whakatuwhenua Stream.
It causes major damage to the environment.
The photo on right shows the eroding bare rocks, denuded
from their original native vegetation by initial burning, weed spraying,
possum browsing and accelerated erosion. At the bottom of the slips the
sea carves their spoils out, leading to mud clouds at every spring high
tide. In the foreground the water is in dense plankton bloom, foaming in
the process. Visibility under water would be less than 2m, which is degrading
f980200: the steep pancake coast, and in the foreground thick
dirty foam produced by the dense plankton bloom underneath.