Dr J Floor Anthoni, 2005
The biodiversity of Niue was for many millennia
influenced by natural forces but more recently also by humans. In this
chapter we'll examine all these influences and how they have shaped Niue's
principles: biodiversity is caused by
the processes of evolution, whether natural or human-made. It is important
to recognise the many factors involved.
principles Biodiversity is the long-term result of evolutionary forces which can
be natural or originating from the way people interact with nature. On
a small island like Niue, both have had important consequences. The way
organisms change or adapt by evolution works like people breeding better
plants, flowers or livestock, simply by selecting the ones to survive.
In the case of breeding, people do the selection and in the case of evolution
it is done by nature. Both result in the survival of the fittest,
meaning the types with the required ('better') characteristics. To better
understand the principles of biodiversity, visit the important biodiversity
chapter on this site.
Niue is a very small island in the large southern Pacific Ocean. Ocean
surface currents flow mostly with the trade winds in a north-westerly direction,
arriving from a cooler area of the Pacific without neighbouring islands.
But occasionally a reversal happens. During such instances, larvae or mature
animals from neighbouring islands to the north may arrive at Niue. The
gene pool in Niue is thus periodically updated, preventing unique endemic
species to evolve here. Thus Niue is not likely to play a role in the world's
biodiversity and it is unlikely to find species here that are found nowhere
else in the world.
When species arrive in Niue's coastal seas, they are subjected to the
following deselecting influences:
temperature: the seas around Niue are cool for the tropics, as cool
water arrives from the south-east. It limits growth and deselects species
unable to cope with these temperatures. Thus many species from warmer waters
are unsuccessful in establishing themselves at Niue.
small area: Niue has very little hard shore, the place where most
marine organisms are found. So there is precious little room for large
numbers of each species. This has serious consequences and deselects those
species unable to cope in small numbers on small territories.
poverty: the clear blue water contains very little food. Energetic
and wasteful species such as sardines cannot possibly live here. It deselects
the energetic and wasteful species while selecting for frugal ones who
also expend little energy by being 'lazy'.
isolation: on the one hand Niue is insufficiently isolated to produce
its own endemic species, but on the other hand is sufficiently isolated
in a large desert ocean to cause persistent recruitment failure. This has
selected for animals that grow old or care for their brood or have some
other strategy to cope.
hurricanes: hurricanes bring large and deep waves that destroy the
shores in their path. The sheer speed of the water when it shears over
the shore is enough to water blast all soft life to death, and the rubble
in its path scours coral structures to their basic shapes. Although large
hurricanes are very infrequent, they nonetheless have a prominent and lasting
effect on the northward shores of Niue which they lay barren, to
be grazed by tangs and urchins.
trade winds: the opposing side of Niue is constantly buffeted by
a swell which has an equally important influence on the life below and
the shape of the coral slope. It creates shallow barrens as it is
not strong enough to create deep ones.
exploitation: on land the natural species have been exploited in
many ways, and the sea has always been fished. The coralline reef flats
have particularly been harvested intensively.
the slush hypothesis In 2005 we discovered a
new method to measure decomposer activity and biodensity in sea water.
The Dark Decay Assay (DDA) has been
treated extensively in its own section. With it we proved that the degradation
in the sea is mainly caused by an imbalance between the nurturing and the
bacterial side of the plankton. We also discovered that natural decomposition
cannot complete because the energy locked up in biomolecules is insufficient
to decompose them. What remains is a group of organic molecules we call
as in incompletely molten snow. In July 2005 we measured the sea water
around Niue and established that although it has almost ten times less
phytoplankton than the sea around New Zealand, it has a large amount of
in fact equating to half the phytoplankton around NZ. Slush is neither
food for plants nor animals, nor is it food for bacteria unless another
form of energy is added to help them decompose it further. Such energy
can be provided by plants alone when living in symbiosis with decomposing
bacteria on their skins. Animals with plant cells and bacteria combined
(mixotrophs) can decompose the abundant slush and become
very productive, even though the water is so devoid of plant and animal
plankton. It explains the success of corals and the algal slime covering
the barrens of Alofi.
Please note that the slush
hypothesis has not yet been confirmed by traditional science.
On land, nature has very similar influences. Sea birds for instance
are too wasteful (energy-spending) to survive here because they depend
on rich sea life in the sea around Niue. On land we can recognise the following
isolation: Niue is sufficiently isolated for most forms of life
by the 500km of ocean between it and the nearest islands. But birds, bats
and plant seeds can be brought there by cyclonic winds. People found it
only some 1500 years ago. The plant and animal communities on Niue are
thus not easily disturbed by natural newcomers.
small size: Niue's land surface (260km2) is very much larger than
its rocky shore (4km2) but even so, this is insufficient to maintain the
biodiversity of a tropical rain forest. Furthermore, Niue has four distinct
habitat zones extending from the reef flats towards its centre.
moisture/rainfall: Niue receives about 2m of rainfall, about twice
that of Auckland, New Zealand. But the soils cannot retain it as it seeps
quickly down into a labyrinth of channels eventually leading to the sea.
Niue has no creeks or rivers, no springs no wetlands.
droughts: Niue has a wet and a dry season but occasionally two or
more successive years of drought, which upsets life on the island considerably.
winds: steady trade winds of 15-25 knots (25-45km/h) blow from the
southeast for most of the year. In the months with the warmest water in
the tropics (Nov-Jan) a tropical cyclone may descend on Niue with variable
strength. It brings very strong winds (120-300km/h) capable of stripping
leaves from branches, felling trees and blowing insects and birds off the
island. Powerful cyclones like Heta leave a lasting influence.
soil: Niue does not have volcanic rock or soil. It consists of a
coral limestone rock extending at least 100 metres under water and 70 above.
Niue's soils were formed in a very slow process by the weathering of coral
rock under a canopy of vegetation. Where forest trees stand, the soil is
deepest and in the coastal saltspray zone shallowest.
In addition to natural influences, people have also
made important changes to what lives on Niue:
selecting useful species: everywhere in the
world, already in their nomadic stage, people have knowingly and unknowingly
promoted the species of use to them.
by clearing competing species around them
by collecting fruits and seeds and spreading these
by defecating in the areas of productive species
and thereby fertilising them
introducing wanted species: when settling
on a new island, people brought important food crops with them such as
the taro root. Edible and ornamental species were also traded between islands.
introducing unwanted species: wherever people
went, they took with them unwanted species such as flies, rats and weeds.
Also on Niue chickens went wild.
introducing noxious species: often wanted
food species spread, upsetting the natural environment. cats, chickens
and pigs have caused much damage. It is feared that the introduction of
honey bees has been detrimental to the population of colourful parakeets
who also depend on honey for sustenance.
habitat change: in order to suit the environment
to their needs, people have always made habitat changes for dwelling, cultivation,
roading, fortification and so on. With the aid of fossil fuel this could
be done on a grand scale. In Niue most of the land has been changed but
some natural areas remain.
slash-and-burn: slashing the new growth and
burning it has always been part of shifting agriculture, Niue's predominant
way of cultivation, but arrowroot (an important source of starch) was always
the first to emerge after burning. When the traders expressed interest
in arrowroot, wildfires became a new way of life, encouraging the regrowth
of arrowroot. As we now know, this had a disastrous effect on the soil's
quality as valuable nutrients also went up in smoke.
exploitation: in addition to habitat change
for cultivation, people exploited the natural world by hunting. On Niue
the most important hunted animal species are: fruit bats, coconut crabs
and birds. Many plant species are exploited, particularly for housing,
canoes, weaving, food and more.
emigration: with Niue's population steady
at 4000-5000, the locals were living within ecological boundaries, exerting
a high pressure on the environment. But after World War Two most left for
better pastures in New Zealand and Australia. At the turn of the millennium,
20,000 Niueans were living in Acukland, leaving about 1000 to mind the
island. This significant emigration has relieved the pressure on resources,
giving both the land and nature respite.
habitat zoning on land The
diagram shown here simplifies the natural habitat zoning on Niue, both
above and under water. It shows a cross-section from roughly SE to NW such
that the hurricane side is on the left side and the trade wind side on
right. From left to right the following habitat zones can be distinguished:
Alofi underwater barrens: occasional tropical cyclones destroy coral
life, resulting in a barren seascape to 70m depth, which is kept barren
by incessant grazing of sea urchins, surgeonfish and parrotfish.
Alofi reef flats: coralline reef flats just above low tide level,
heavily exploited by the practice of reef gleaning and collecting. During
high tide this area is heavily grazed by surgeonfish.
Alofi terrace wind-struck rain forest: hurricane winds cause a heavy
toll on the natural rain forest. This habitat has also been modified for
Mutalau ridge rain forest: a remnant of the original rain forest,
not suitable for cultivation.
Fern lands: clearfelled rainforest and soils cultivated for food,
resulting in fern lands.
Huvalu rain forest: a central lagoon remnant of the original rain
forest. The remaining area of Huvalu high forest is estimated at 6000 acres
(2400ha) with a tapu area of 40 acres (16ha) within, now protected for
Mutalau ridge rain forest: as above but this side adjoins to the
unmodified saltspray vegetation, a haven for the coconut crab.
Saltspray karrenfeld and vegetation: because the rainforest never
stood here, soils are poorly developed leaving an inaccessible terrain
of sharp coral pinnacles and sink holes (karrenfeld) with low vegetation,
dominated by salt-tolerant shrubs such as Pandanus mangrove trees.
High pools: as the trade wind swell bursts skyward, it deposits
water on ever growing deep rock pools, the mysterious high pools with their
own miniature ecosystems.
Trade wind barrens: the trade swell is not powerful enough to create
deep barrens but only a short ledge and step. This shore shape breaks the
swell by bursting it skyward and bouncing it back to sea.
The tradewind coral slope: a gradual slope of healthy corals with
rapid water movement down to 20m. Although corals thrive, fish dislike
the continuous water movement.
map shows the actual location of Niue's vegetation types. It distinguishes
two zones, the coastal zone and the inland area. The coastal zone covers
the salt spray zone, the coastal forest and coastal fernlands. The inland
area covers regenerating forests and fernlands and the high rain forest.
As one can see, the amount of original vegetation is not large but relatively
larger than that in New Zealand. The Huvalu Forest Park covers both regenerating
and original forest and may take several centuries to regenerate fully.
Click here for a larger version of this map: niue11m.gif.
habitat images Below follow a number of images of the various habitats on and around
Niue. It follows the habitat diagram from the hurricane side to the trade
f044601: the Alofi underwater barrens are created by large
storms and maintained by a large variety of grazers.
f044913: small black needle urchins inside their sockets
waiting for the night to emerge when they graze their gardens.
f220937: the coralline reef flats found mainly on the Alofi
side of the island.
f223011: reef gleaning for sustenance is still widely
practised. The coralline reef flats do not consist of corals but coralline
algae, covered in a sum of brown-green slimy algae. Mysterious rock pools
break the surface.
f222925: the Alofi terrace is frequently hit by hurricanes,
low, salt-resistant shrubs survive.
0507008: on the hurricane side, tall trees are occasionally
stripped, which selects for the most suitable types.
f221229: where good soils are found, people strip the vegetation
for cultivating taro crops. Here the fields are left fallow to recover.
f220516: a prosperous taro crop.
0507450: the author and Misa by a tall forest tree with buttress
root stabilising it against hurricane winds.
0507451: tall forest trees are still found in the Huvalu
0507470: the fou tree (Hibiscus ) was used for making
0507140: coconut palms grow all over the island but are promoted
near settlements and on soils unsuitable for farming.
f223222: the coastal rain forest grows where jagged rocks
f220816: pandanus mangrove trees are salt-resistant and thrive
in the saltspray zone.
f220733: salt spray from incessant large swell has created
a moon landscape of very sharp jagged rocks with salt resistant vegetation.
f223220: a salt-resistant perennial weed grows where no other
f220503: the swell is thrown high skyward, causing copious
amounts of salt spray (Anaana Point).
f044715: underwater on the tradewind side extends a slope
of healthy corals. The large giant clam seen here enjoys de-facto protection
by the waves.