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Two contrasting
areas were examined as part of the Reef
Check program. These are the channels
that lead out of the lagoon to the open
sea, and the reef crest which forms the
seaward margin of the surf spot and
drops steeply into abyssal depths. Both
are dynamic environments with high
current and a habitat where life clings
to a steep slope, which is more
characterised by skeletal remnants of
living reef than the existing corals and
other organisms.
The inner lagoon of the atoll is
connected to the open sea by a 25m deep
by 150m wide channel. This and the other
channels of the atoll are responsible
for the lagoon’s water exchange and
circulation. The crystal clear lagoonal
waters host a bounty of black pearl
oysters. With current velocities of 2-6
knots, large volumes of water are driven
by tide, wave and wind currents to make
this area one of the atoll’s most
inhospitable environments. With steep
sides, composed largely of rubble strewn
down the slope, life perches
precariously to the unstable substrate.
Corals are relatively few, making up
only 10 per cent cover, with other
bottom dwellers like hydroids and
sponges conspicuous. Oddly the marine
plants are present only as thin covering
on the boulders and rubble, attesting to
the nutrient poor waters that normally
characterize the coral reef environment.
Forming a crust along the channel rim is
the consolidated reef flat. Here it is
seen to be crumbling at its margin with
its fragmented coral pieces cascading
over the edge and into the channel
depths.
In an unexpected way, the barren rubble
shows something of the reef’s health
with a myriad of small colonies
developing. Of particular interest is
the abundance of the Acropora colonies,
which were nearly entirely eliminated
from the reef flat during the coral
bleaching event of two years ago. Now
with colonies at one and two years old,
these corals will be providing planula
(larval or young corals) for the atoll
as the fast moving currents sweep them
into other, perhaps distant,
environments. The natural process of
rejuvenation is no more evident than in
this channel environment.
Fish are abundant along the channel
crest. Man’s influence, apart from the
remnants of fish traps, appears minimal.
The jetties, used for servicing the
oysters, provide a habitat where fish
congregate beneath. The village of 400
people, apart from a moderate concrete
wharf, shows no sign of nutrient
pollution with its symptomatic
proliferation of fleshy alga. Why?
Dilution cleanses. With such rapid
currents, all that enters the adjacent
waters is rapidly sent out to sea. This
goes for the village garbage that is
cast to the depths (600m) just outside
the surf spot. Homes for small fishes
and other knickknacks, never to return
again.
The reef crest, which margins the surf
spot to seaward, is in many ways the
same environment as the channel. Though
at 10m depth, it has a crest which drops
precipitously with an incline of 60-70
per cent into dark blue abyssal depths.
The living cover is at its maximum here
with a coral coverage of 80-90 per cent.
This exists as a band of 10m wide
luxuriant coral which extends along the
crest. With depth (25m), the coverage
decreases with corals and other
organisms much less abundant. As with
the channel, loose, non-living reef
material becomes the dominant substrate
as the slope steepens. In this case, it
is sand and not rubble. Created by wave
action on the reef flat, constant rain
silt is continuously being carried off
the shallower reef terrace by current
and swell action. With the wave-washed
reef terrace, a combination of hard rock
surface (coralline algae) and numerous
corals (largely Pocillopora meandrina or
eydouxi: -50 per cent coverage), all
broken coral, is either deposited on the
shingle-mounded beach or consigned to
the depths off the reef crest.
As with the channel environment, schools
of fish abound at the reef margin.
Paddletail snapper cruised in a school
of 400 plus, with Jobfish and Milkfish
in the bluewater.
In summary, this is an environment of
low human impact despite a full-scale
pearl farming operation and a large
village. The key to the pristine nature
of the atoll environment is the amount
of water that vigorously circulates
around the atoll. Coral bleaching has
had a major impact on the hard coral
community structure and, though there
are residual occurrences, the reefs
appear to be regenerating.
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