Saturday, August 28, 2010

My next passion:SHELTERED SHORES: Harbour, Estuary & Mangrove

Ecologists now see the coastline as a series of habitats which fall into two major
categories: those that are sheltered from the wind energy of the open ocean and those
exposed to its full force. Modern man threatens each habitat with a special set of
problems. We must learn to appreciate these marine worlds and to live within them
without causing harm. As so many life forms rapidly become extinct, we are realising that it is no longer individual species we must protect, but their entire habitats.

From an ecological viewpoint, the richness or biomass of coastal habitats depends on
their stability. Sand and gravel beaches provide an insecure and shifting environment for a reduced range of life forms. Those adapted to a burrowing existence form very dense populations in such areas - pipis and other bivalves, tube worms and swimming crabs. Further up the shore the sand dunes provide a very fragile habitat in which the least disturbance of plant cover can cause erosion. (In Holland access to beaches across sand dunes is now restricted to foot bridges.)

The boulder beach is the harshest life zone of them all. Every storm tosses the big stones around and rubs them together, giving them their clean, close-grained surfaces. Despite the diminished range of organisms in such areas, life is tenacious, and small, fast-moving creatures such as crustaceans manage to find refuge from predators among the boulders and feed on the life-giving currents.

The richest marine worlds are the most sheltered parts of our coast: our harbours,
estuaries and mangroves. Mud is the basis of it all: the messy places we insist on “tidying up”, the mud flats we reclaim, the inlets we straighten with causeways, the swamps and wetlands we drain for pastures, all the gentlest meeting places of land and sea, are the “black gold” of tomorrow.

In thick, black mud thrive millions of bacteria which readily convert decaying matter into
nutrients, a process on land well known to soil technologists.  The difference between
clay and fertile soil is the presence of countless useful bacteria which convert animal
manure and leaf mould into plant food.

From exploring the riches of the mangrove community
by day and by night I continued into the estuary, river
mouth and harbour, tracing the energy pathways created
by this highly diverse part of our coastline.  This is the
region where living conditions are optimal: abundant
shelter, sunlight and nutrient supply result in complex
communities that are most accessible for us to study and
enjoy.  Here, on our doorsteps, we can experience a
complete biosphere from sea plants to trees; mosses,
lichens and epiphytic ferns; shellfish, crabs and shrimps;
fishes galore; insects and birds.  For my wife Jan and
me it was as satisfying as the coral reefs and offshore
islands we have explored.  This CD Rom is the result of
over thirty years during which we have collected images,
video and first hand experiences.  To fit on here my
movies, more than an hour long, are highly compressed.
Please regard them as a bonus sampler. High quality
versions are available on DVD disc: 

Harbour Riches    Wade Doak
I have descended thirty metres down the tumbled rock walls of a small island just within
the entrance to Whangarei Harbour - “meeting place of the whales”.   Aubrey, Passage or
Motukaroro Island now a Marine Reserve, is about the size of a large cruise ship but much 
beamier: 200 x 100 m.

It lies 18 kilometres downstream from a city; 300 metres from a major oil refinery and
supertanker port.  Twelve hundred hectares of mangroves and vast expanses of mud flat
and channels drain their nutrient riches through a deep, narrow throat beneath the crags of
a mythic volcanic mountain.

Around me in the half light, ghostly white, cardboard thin john dories, squadrons of them,
stalk their quarry.  Jack-in-a-box jaws flash open and shut. I cannot see their prey in the
gloom. I glimpse a school of silvery snapper at the edge of vision.
I have hiphopped ten storeys from the pohutukawa trees overhanging the calm water’s
edge, where herons and gulls in the glow of the late sun wait out the high tide and the
return of their intertidal feeding zone.  I’d stepped from our inflatable onto a knee deep
flat rock. Jan passed the video camera and I slid in.   Surprisingly warm - even for late
autumn.  Quite turbid with a high load of visible particles.   A hazy five metres of vision.
Initially I felt a little disappointed.  Nowhere near as clear as my beloved Matapouri
mangrove creek, nor Whangateau’s blue channel.  But I wanted to check out this location
as perhaps the acme of mangrove productivity and export.

Kelp fronds on short stems, coated with silt. Richly encrusted rocks.  Weed eating
parore, drummer and butterfish darting among the canopy.  Myriad juvenile spotties with
bright yellow markings nipping at life on the kelp leaves.  Then a swarm of oblique
swimming blennies, [triplefins] plankton feeders from the open sea.  And demoiselles nipping at the
current, flitting about with their scissor tails like undersea swallows. Even small blue
maomaos.  I never dreamt of seeing such oceanic fishes within a harbour.

At ten metres an abrupt transition: the kelp forest stops and encrusting life expands, along
with a dramatic increase in reef fish, both in variety and abundance.  The profile is steep
but not vertical: big volcanic rocks with sandy terraces.  These rocks often have flat faces
and over them jewel anemones spread in sheets of opulence: each colony of the same
colour: mauve, wine red, apricot, green, lolly pink - exquisite, vibrant hues that seem to
fluoresce as the light diminishes.  I feel I am on a coral reef.

At 15 metres I just stop and stare in amazement.  The density of fishes is unbelievable.
Above me the sun is dimmed by a cyclone of jack mackerel that weave around me in a
living cylinder.  Like sharks, out of the gloom massive, bullet shaped bodies whirl in to
scrutinize me: large kingfish in squads of five to eight, bigger than I have seen for some
years.  Among the rocks, in hollows and near ledges the reef fish are busy.  I do a video
run trying to compress the diversity of species into a brief time frame.  A butterfly perch
and a triggerfish cross my screen, giving way to a skittish lumbering marblefish and a
weaving group of large spotties and scarlet wrasses.  A big male banded wrasse dashes to
and fro in a rocky alcove.  I veer to the left: a red moki rests beneath a ledge.  It exits and
I follow close to its broad tail as several triggerfish and wrasses cross my path towards an
overhang where slender roughies and big eye, night plankton feeders, dart around in the
gloom, awaiting dusk.  My sequence finishes on a mottled blenny resting on a rock like
an owl.

Then, beneath the ledge I notice a long-legged, red rock crab, its ornate carapace reminds
me of the cockney pearly kings who decorate their clothes with shiny buttons.  While
crabs often flee the camera this one is big and shows no fear.  I watch its elaborate mouth
parts flicking as it combs the water for plankton.  Then it reaches up, grasps the rock
ceiling and swings up so that its tail is towards me.  Upside down it rotates to face the
camera and resumes feeding in a topsy turvy pose.  Nearby a pair of ghost shrimps waft
like sporty helicopters.

Amidst the anemone colonies nudibranchs crawl and triplefin blennies pounce and roost:
mottled, masked, lined, banded, crested, yellow-black - a variety to equal any offshore
island scene.  A pair of mimic blennies hover sinuously, trying to bite the sides of a
spotty who may be deceived into thinking these pirates are just harmless oblique
swimming blennies.

In a sandy mall I meet a herd of goatfish more numerous than I have ever seen before and
the adults are huge.  This sand must be rich in the micro fauna that they dabble and delve
for with their taste bud bearing barbels.

Glenn Edney, leading marine photographer, who has dropped down the slope nearby, is taking still photos with slow, quiet precision.  We keep clear of each other to avoid problems but a squealed signal
attracts me. He has found an octopus.  He holds out his hand, palm uppermost. Its head
flushes a variety of colours.  Then it extends a tentacle and palps Glenn’s palm gently.
We’ve been accepted by the local intelligentsia.

But there are even bigger brains in these waters.  One day while concentrating on the
viewing prism of his Hasselblad camera veteran photographer Warren Farrelly heard a
weird sound behind him.  An immense orca was looking over his shoulder.   Orca
regularly visit this harbour to hunt the stingrays that feed on molluscs over the flats:
“Meeting place of the whales!”

In the deep zone the encrusting sponges become erect and impressive.  Yellow
stalagmites; long finger sponges, organpipes and orange spheres.  Pale feathery plumes of
a hydroid colony like an elaborate hat.  A gnarled Solanderia hydroid tree like a Chinese
bonsai miniature.

With the outgoing current gaining force I surface near dusk.  Shortly this spot will
become a maelstrom, water piling up against the island as on a tanker’s bow.  I take stock
of the thriving world below my fins.  In terms of biomass and species diversity the reef
fish population around this tiny island would equal most locations in New Zealand’s
richest area, the Poor Knights Islands, but not their overall diversity.  And the fishes
would be an indicator of the diversity of the encrusting life.  Aubrey, with its powerful
currents, lack of wave violence and the enormous nutrient riches of the adjacent
mangrove forests, must be one of New Zealand’s hot spots for reef fish life - a regular
sky tower Casino!

A more detailed survey of the fish life, greatly assisted by local diver/photographer
Warren Farrelly, gives a fish count of some 50 species for the area, extraordinary for an
enclosed harbour site and a tribute to the immense power of mangrove productivity.  No
wonder that Warren and his pupils at the nearby Kamo Highschool fought for 15 years
to make the island a marine reserve, along with an area of mangroves and an expanse of
inter tidal mud flats up harbour.

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