|New Zealand is a special place on Earth, because on the Southern Hemsiphere, very few large islands exist. For the same reasons the Kermadecs, Norfolk and Lord Howe are special in the Pacific subtropics (on this page)|
|The seawater temperature has an enormous influence on the creatures who live there, because they cannot regulate their body temperature. (on this page)|
|Winds and currents determine the climate and the direction in which larvae will drift. (on this page)|
|The fertility of the sea is not distributed equally. The Kermadecs are located in an infertile zone, but a steady supply of nutrients is possibly present. (on this page)|
|The reason that brown kelps are not found here, is a mystery that is explored in this chapter. (on this page)|
|A number of relevant habitat photos. Visit the photo gallery for more. (on this page)|
|A short overview of the terrestrial ecology (on this page)|
|Related pages on this web site:
Why NZ is so special: a summary of what makes New Zealand a special place.
Oceanography: An explanation of clockwork Earth. Relevant to all sections.
Note! for best printed results, set your page up with
a left margin of 1.5cm (0.6") and right margin of 1.0cm (0.4")
For corrections, suggestions and improvements, e-mail me.
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|A special place
New Zealand occupies a special place in the World's natural affairs, as can be seen from the map on right. This is a view of the globe centred on the South Pole. Three main continents can be seen extending hesitantly southward: South America, Africa and Australia. But they are separated by insurmountable distances, reason why their flora and fauna differ completely. Also their marine environments have nothing in common, even though marine creatures could swim from one continent to the other. The reason they cannot do so, is that they won't survive the trip, as the blue seas are water deserts, with too little food. Only the largest of marine creatures, having enough spare fat, and the advantage of scale, can make it.
matters much to creatures that are unable to regulate their body temperatures.
Metabolic activity of enzymes changes remarkably with a change of 6 degrees
in temperature, which is the main reason that climate bands are found from
the equator to the pole. Although land temperatures vary wildly from day
to night and summer to winter, the sea's temperature is far more stable.
Yet in NZ, considered of temperate climate, a seasonal swing of 6-8ºC
can be observed. For the Kermadecs this is a little less (6ºC).
|Winds and currents
The drawing on right sums up the world circulation in the atmosphere (See oceanography/circulation). It shows that the circulation patterns change drastically around 30º latitude. In the tropics, the trade winds blow towards the equator, saturating with moisture. They then rise and release their moisture, circulating back to the subtropic high and descending as dry air, creating desert zones. The Kermadecs are located in this area, experiencing trade winds in some seasons, and westerly gyres (as in NZ) in others.
|This diagram sketches the basic currents around New Zealand (See oceanography/New Zealand). As mentioned before, the South Pacific ocean circulation (gyre) pushes warm water down Australia's eastern shore, where some splits off along the tropical front (TF), as it meets cooler water travelling north. Importantly, it shows that the general direction of all currents is eastward. On the map, three subtropical island groups can be seen, from W to E: Lord Howe Island, Norfolk Island and the Kermadec Islands. The direction of the current suggests that eggs and larvae of marine species travel mainly eastward, and that the reverse is unlikely. It can explain why Australia has practically no NZ species, but NZ has some Australian species. Note also how the sub-antarctic islands are isolated from NZ by the Sub Tropical Front (STF).|
This diagram shows the layering in the ocean and its deep circulation, which is not important here. Due to high surface temperatures in the tropics, the surface water is lighter than the deep water, resulting in a thermocline at 100-200m depth. This thermocline prevents nutrients from resurfacing, resulting in infertility of the sea at its surface. In the subtropics, evaporation is high, resulting in slightly saltier surface waters (see map in oceanography). The Kermadecs are located here.
|The net effect is that like the deserts on land (yellow), similar deserts are found in the oceans (deep blue) at roughly the same latitudes, as shown by this satellite image of actual chlorophyll concentrations, representing the amount of plant life, on which all other life depends. Tucked away in the righthand margin is NZ, blessed by rather high fertility in its seas. But the Kermadecs lie just outside, as the detail map below shows.|
map is an enlargement of the one above, with left and right margins joined.
It shows how New Zealand's seas are relatively productive, with a peak
off Kaikoura, east off the South Island. The Kermadecs jut out into the
blue desert, but some peculiar mixing is noticeable.
Experimenting around the ocean ridges of the Hawaiian chain of islands, scientists have discovered  that the tide wave, which raises and lowers the water along continents twice daily in the rhythm of the moon, causes deep currents when hitting the Hawaiian ridge head-on. These currents disturb the deep thermocline, bringing nutrients to the surface. A similar situation is likely present at the Kermadecs, and indeed, satellite images  have shown a noticeable distortion in the tide wave, the cause of local ocean currents and swirls. When diving the Kermadecs, these strong currents are very noticeable.
The conclusion is that, although the Kermadecs are located in a blue water desert, a slow supply of nutrients makes it to the surface, supporting not too abundant life.
 Hawaii Ocean Mixing Experiment (HOME). Rob Pinkel,
Scripps Institution of Oceanography.
 Egbert G and Ray (2001). Global distribution of barotropic tidal loss. In: Aspects of deep ocean mixing, Chris Garrett and Louis St Laurent. http://maelstrom.seos.uvic.ca/people/lous/japan/paper.html
sizeable land masses, such as New Zealand, most of the nutrients in the
sea originate from the land. Rocks weather to form soil. In the process,
nutrients are dissolved and washed into the sea. Farming exacerbates the
situation and soil loss even more so. These nutrients feed the phytoplankton
of the sea and the seaweeds on the rocks, on which all animal life depends.
The land mass also provides the mechanisms to keep nutrients from straying
into the abyss of the deep sea:
For a small land mass like Raoul Island, these factors are almost negligible, reason why nutrients originating from the island, are quickly lost. Small islands like this surrounded by a blue ocean desert, are thus destined to look more like a desert than a fertile ground under water, which makes life there difficult, but sea birds may play an important role.
diagram shows how sea birds can play an important role in recycling island
nutrients. It is an advantage enjoyed by outlying islands, because rats,
cats and stoats have driven sea birds off the mainland, allowing them to
congregate on safe, offshore islands. Due to ocean mixing near islands,
which is still poorly understood, there is a slow upward trickle of nutrients
from the deep. Add to this those from island erosion and volcanism and
bird droppings. Rains wash the nutrients down, causing phytoplankton to
bloom in pockets around the island and further down-stream (left). Living
from this phytoplankton, shrimps multiply their numbers, and these are
eaten by fish. Both fish and shrimps are caught by sea birds, who spend
some time on the island, emptying their guts overnight. In the cycle, the
sea soil, and planktonic bacteria in the water help to recycle nutrients
from dead animals and wastes. But overall, some (or most?) nutrients are
lost to deeper water.
How large the influence of birds is on this nutrient cycle, is unknown. It would be interesting to monitor the fish life around Raoul, as its bird numbers increase. It could well be possible that this has a large and beneficial effect on the sea life there, but there is yet another factor.
|Corals but no kelps
Why is it that the Kermadecs have no kelp plants? Why is it that our luxuriant kelps, growing the full length and width of NZ, do not grow here, only 800km further north? Surely evolution would have been able to adapt them or some relative for living here? The difference in temperature is only 3-4ºC. And why is it that so many of our NZ fish species can't live here either? We'll try to answer this question, because it lies at the very heart of understanding the islands' marine ecology, but first a disturbing observation.
We noticed symptoms of (serious) environmental stress. How is this possible
in a pristine environment so far removed from human influence? Would global
pollution be to blame? The volcano perhaps?
Stress on the natural environment is hard to quantify, and very few people would be able to recognise it as such (See also the chapter on Marine Conservation and principles of degradation). But a number of stress indicators can be observed clearly, and taken together, form a picture, even if this is only a mental picture. The stress symptoms we observed were the following:
|Our observations lead us to conclude:
Only long-lived species which live frugally,
The marine environment around the Kermadec Islands is fragile and
Our only option is to protect it completely
|The reason that large brown kelps like Ecklonia radiata and
Carpophyllum species are absent, is perhaps manifold, and
needs further investigation:
The small size of the islands poses another problem, that of insufficient habitat space. Although the marine reserve proper measures 7480km2, this is overwhelmingly empty space. Raoul with its 31km2 land area, has probably no more than 20km of rocky shore, including all the islets around it. Most of this consists of boulders bordered by a shallow sandy bottom, razed by ferocious waves. For the giant limpet, which grows with densities of 2-6/m2, perhaps only 10km of suitable habitat is available. Its zone is only two metre or so wide, so a quick estimate of their numbers is ~30,000. This is a small number for a viable population, particularly for a grazer, on which other species should feed. It must not be surprising then, that they do not appear to have natural enemies, and that they grow very old. To increase their survival chance, the large females carry small males on their backs!
Take the giant groupers. They are top predators, living in the slow lane, but also growing very old. Nobody has surveyed their numbers, but my own estimate is 20/km, or a total of 200, plus an equal number of small ones. The large males are certainly sporadic. They are all born female, and change into a male at 1m length. This makes them rather vulnerable to exploitation.
It follows then that the gene pool (variability within a species) of the species at the Kermadecs is rather homogenous, because:
Scientists have sampled the coral species at the Kermadecs, and found
that at Raoul in shallow water of 1-6m depth, the coral cover can reach
20-40%. South of Raoul, the coral cover reduces dramatically to less than
There are 17 hermatypic (zooxanthellate) species and 7 ahermatypic at Raoul, but only 2 hermatypic and 2 ahermatypic at l'Esperance. It shows that even corals are not very successful at this latitude and loneliness.
Of the close to 400 species of mollusc found, some 20% is thought to be endemic, and all other species are probably stragglers (allopatric), not normally breeding here.
The one really successful marine creature is a coralline alga (Lithtohamnion sp. =stone-leaf), or popularly called pink paint. It is found as a major player on all rocks and all depths we could dive to. Look for it in the many photographs in our photo galleries.
Reader pleas note that all of the above has not (yet) been supported by scientific study and experiment. It follows from oceanographic facts for the area, and personal observations. Please e-mail me should you have additional or corrective knowledge. - Dr J Floor Anthoni
|Some habitat photos
Over 120 photos of habitats, corals and marine creatures are displayed in the photo galleries attached to this Kermadecs section. Here we have chosen a few ecologically important ones.
|The terrestrial ecology
Although technically, the Kermadecs are located in a desert region, they are also part of a weather system influenced by warm currents, cooling as they travel southward, causing rain in the process. On the opposite side of the Pacific, along the coast of Chile, the opposite happens. Here cold currents warm up, causing droughts. In all, these islands enjoy a healthy amount of rainfall, comparable to that of Auckland: 1500mm in the wet season from October to January. the dry season runs in the opposite months April to July. Its temperature ranges from 16.0 in August to 22.4ºC in February. The Galapagos Islands, located near the equator, have a similar marine environment and water temperature, but the islands are dry and desert-like.
Raoul is densely covered in a climax forest of Pohutukawa (Metrosideros kermadecensis), Karaka and Nikau palm (Nikau Rhopalostylis baueriana), from the cliff face to the top of Mount Moumoukai at 516m. The mountains catch more moisture and here one finds a rich variety of mosses (52), ferns, lichens and fungi (89). The forest community here includes Ascarina lucida, Melycitus ramiflorus and Pteris comans.
The native forest hosts 113 native (NZ) vascular plants of which 23 are endemic! The understorey of the forest consists mainly of Myrsine kermadecensis; Lobelia anceps, Poa polyphylla, Coprosma acutifolia, Coriaria arborea.
The coastal vegetation consists mainly of: Myosporum obscurum, Coprosma petiolata, Asplenium obtusatum, Cyperus ustulatus, Disphyma australe, Scirpus nodosus.
Many sea birds have evolved to migrate vast distances, and the Kermadec's isolation is no real obstacle to their distribution. But when they gather in their millions, they also need to be fed, which requires a rich source of food nearby.
Historic accounts talk of millions of breeding seabirds in some seasons, but they have been discouraged by the introduced predators. Still present are 14 species, including 10 that breed nowhere else in NZ, like the Kermadec petrel (Pterodroma neglecta/ cervicalis) and the black-winged petrel (Pterodroma nigripennis). There are 3 endemic breeders.
It is not known how many uniques species lived here before the introduction of alien predators, but the following three species have been extirpated (destroyed completely):
Here are some of the sea and water birds and their seasons:
Passerines (perching birds like sparrows):
Raoul has native bees which are black and very ferocious. They find rich supplies of nectar from the pohutukawa trees, which have a much longer flowering season than the NZ variety. Their honey is of the finest grade, some large hives yielding over 30 litres!
The Kermadecs lie along the migration paths of humpback whales and sperm whales, seen in numbers in the months of October and November.