Sea temperature The map shows global ocean temperatures for the Pacific Ocean in false colours from purple to red. Absolute values for the sea temperature are thus hard to guess but a clear picture emerges. As expected, the sea warms gradually from the South Pole to the Equator in horizontal bands. But these bands are not strictly horizontal, particularly the green one of the subtropics. It curves all the way up to the equator along the coast of South America, due to a strong ocean current moving up this coast. As a result, the Galapagos Islands on the Equator are as cool as Sydney and Melbourne or even Auckland. This tongue of cool water moves just south of the equator as it gradually warms up. Niue is located on the cool edge of the warm tropics but its waters are much cooler than those of Indonesia for instance.

Note that the Sea Surface Temperature (SST) map was produced by infrared sensing satellites that cannot pierce the water's surface (infrared light is absorbed immediately). Thus the SST is indeed the temperature of a very shallow surface layer, ignoring any cooler water direct underneath. One would expect waves to mix the water column, which they do, but in the Niue area, average wave height is rather low, as seen by this satellite map of average wave heights. The bulge of warm water near Niue may thus not at all represent the actual situation. This map was produced from the electrical noise in the reflected radar signal from various satellites. Scientists soon discovered that the strength of this noise related to wave height, which allowed them to plot the wave height map seen here. Note the power engine in the South Indian ocean and south of NZ. This wind and its waves drive the Antarctic circumpolar (going round the whole pole) current, and probably also the South Pacific gyre that affects Niue.

Look at the sea around New Zealand, for instance. NZ is surrounded by a very productive sea because of invisible currents south and north of it. One current runs southward along Australia's east coast, mopping nutrients into the New Zealand area. On its downward course, it encounters a cool sea which forms a cold front, diverting its course to southern New Zealand. Likewise, subantarctic currents experience this as a warm front as they too are diverted towards southern NZ where turbulence causes upwellings of nutrients.  (See ocean/currents and oceans/specialNZ)

(Picture courtesy of NASA SEAWIFS programme)

Such turbulent upwellings occur also along South America's coast as the coastal Peru Current cork-screws along the Peruvian coast. This current becomes diverted by Coriolis forces (due to the spinning of Earth) and follows a straight path on the equator (See Oceanography/currents/defection). Here the Coriolis forces focus its beam horizontally into a narrow jet that sends invisible eddies downward, causing nutrient upwellings along its entire course as it also gradually warms up. Scientists are studying the interaction of this cool tongue and warm pool, as it produces some unexpected pelagic productivity.
The centre of both North and South Pacific are pools of ultra clear water with very low productivity, while also located in the world's desert bands. Evaporation is high, resulting in a higher than normal salt content. Remarkably, this pool of infertile water travels in a NW direction, past Niue. This is probably because of the trade winds blowing in the same direction. Note that chlorophyll-sensing satellites can look down only about 10m into the sea, so they are unable to view what is happening further down.
For instance, it is quite possible that the ultra clear blue water overlays a basement of cool nutrient-rich water in which phyto plankton (plant plankton) can bloom, because the clear water admits so much light deep down. The productivity of this blue tongue could therefore be higher than thought, although always much lower than green water at the surface.
Note that some anomalies in green upwellings have been discovered, for instance a thin line running from NZ to Niue over the Kermadec Trench and Ridge and a cloud around French Polynesia and Hawaii. These are caused by the slow, deep tide waves 'stumbling' over sea bottom irregularities, resulting in surface currents and local upwellings. The map below shows how scientists calculated the dissipation (loss of energy) of the tide wave due to the shape of the sea bottom. It is based on comparing a mathematical model of the tide wave with actual tide heights measured from satellites. In places where this tide wave 'stumbles' (shown in red), turbulence occurs with possible surface mixing and nutrient upwelling. Compare it with the chlorophyll map above. For Niue this model does not suggest remarkable upwellings.

Source: Spalding, M D et al. (2001): World Atlas of coral reefs. Univ Cal Press.

Hurricanes (tropical cyclones) also leave their everlasting mark on the seascape. Ironically, they cause most damage to the side of the island which is also most sheltered. So Niue has no places of shelter, a necessary condition for high biodiversity. As soon as soft organisms have colonised rock space, the next hurricane will wipe them out again. Only in very deep water can soft and old organisms survive. We have not been able to investigate these deep reefs.

New Zealand's Kermadec Islands live in a similar predicament, although surrounded by a richer sea, sufficient areas of shelter and flats that function as small continental shelves. We observed signs of stress even though there are no unnatural threats such as those caused by people (See marine reserves/Kermadecs). In Niue we encountered the same signs of stress but more pronounced:

• Few juvenile organisms and missing year classes. The juveniles of almost every marine organism are usually the most sensitive to pollution and other stresses. Spawning is a delicate event that can go wrong in any of its many stages. When successful all along this chain, it results in recruitment (juveniles settling from their planktonic stage). Year classes are sometimes hard to assess, but one can almost always distinguish five age groups: this year's babies, last year's juveniles, young adults, mature adults and old adults. What we observed was that there was ample evidence of (serious) recruitment failure in all organisms observed.
• Large sessile organisms removed but not replaced: Open space on the rocks is very precious real estate. In a healthy environment, it is almost instantaneously occupied, often immediately with opportunistic invasive species like barnacles or seasquirts. Because such opportunistic species don't live long, but reproduce fast, the rock space eventually becomes available again, during which time more permanent species have found it. We found an unusually large part of the rocks unoccupied. Ironically, Niue has hardly any invasive species. Even the barnacles and seasquirts are largely missing!
• No schools of small pelagic or semi-pelagic fish: We found no schools of pelagic silver fish like pilchard, koheru, jack mackerel, trevally, and their fast and voracious predators. But hanging close by the coral fringe we found banded flagtail (and juveniles in rock pools!), grazing grey mullet (2 year classes!) and small schools of piper, a zoo plankton eater. Occasionally a small school of truly pelagic fish was visible in the distance.
• Poorly grazed algae: Although there are grazers like drummers, turtles, sea urchins, top shells, parrotfish, surgeonfish and others, many rocks remained poorly grazed. Such an observation may point to poor replacement, or a recent mass die-off, but it may also be a normal situation after good growth in summer (we were there in winter). We suspected slow replacement of grazers who died recently.

We also observed that the predators like small groupers were few and far between, pointing to intensive fishing in places where we dived. All fish, dolphins and turtles were rather shy, indicating the presence of spearfishers. If Niue wishes to become more attractive to visiting divers, places must be set aside where fishing (and gathering) is prohibited at all times!

• growing old: because reproduction has a low chance of success, age should make up for this, as it creates more opportunity for a successful recruitment. Nearly all reef fish, even the small ones, do this. Short-lived 'silver fish' like mackerel are absent, as are invasive species such as barnacles and seasquirts. There are many 'tricks' for growing old:
• being poisonous at times: The tangs (surgeonfish) and parrotfish, as well as some wrasses, can become poisonous by being infected by the ciguatera fish poison. It discourages predators like humans. One finds large old parrotfish around Niue.
• poisonous spikes: the tangs (tang= sharp spike) have a sharp and often poisonous spike embedded inside their tail stocks. By bending their tails, this spike protrudes and can inflict serious wounds, demanding respect from predators and humans.
• poisonous organs: the puffers have poisonous organs which protect them from being eaten.
• being distasteful: it is not known how many species taste aweful, but the famous Spanish dancer sea slug is one of them, and perhaps also several sea cucumbers and anemones.
• coming out at night: the night shift which hides by day but feeds by night, is well suited to grow old, as most predators hunt by eyesight. However, sea snakes hunt by smell and squid are also night-time predators.
• nest care: rather than spawning in open water, small fish benefit from caring for their eggs until these hatch. Many such nests are made in the protective shelter of rock pools where plankton productivity is higher due to higher temperatures, reflected light from coralline flats and nutrients percolating from the land. Some may lay their eggs inside their burrows and guard over them. Burrowing species are found on the few sandy flats.
• mouth-brooding: the males of cardinalfishes, of which there are many in several species around Niue, suck up their mates' eggs after fertilisation and keep these in their mouths until they hatch, for a period of 1-2 weeks, depending on water temperature.
• egg carrying: many organisms carry their eggs on their bodies until they hatch: all crustaceans such as the local crayfish, the cleanershrimp and shore crabs.
• turfing roots: because the water is comparatively cooler than in the warm tropics, and because of the regular damage from cyclones, turfing algae are the primary survivors. They multiply asexually by means of running roots, so their pelagic spores are not of critical importance. Most of the reefs are constructed by coralline algae, known as 'pink paint' that thrives better than the corals. The pink paint encourages the growth of fine algae that are easily removed by many grazers, from snails to sea urchins, to grazing fish.
• living from algae: since the main food around Niue is produced by short algae, all species adapted to eating plant food, survive better and in higher numbers. Even omnivores such as the local green crayfish, thrives on algae.
• hiding and homing: the ability to hide and to home back to one's hiding spot, is of critical importance to survival. Any night dive shows just how many animals exhibit this behaviour, from grazing snails and cowries to sea urchins, feather stars and grazing fish.
• leaving the water: leaving the water during averse conditions is a good strategy available only to few animals. The sea snake knows places where it can leave the water, often inside underwater caves where it also lays its eggs. The land crabs no longer need the sea, except for their offspring, and this includes the coconut crab (a large hermit crab without a shell). Several shore crabs can leave the water for some time.
• burrowing and living in tubes: the coral rock is relatively easy to dig into because it can be dissolved by acids. Sea urchins are particularly successful at this. Others cement their tubes to growing corals, using the coral as protection. These include snails, fan worms and crustaceans.
• being robust: some organisms can grow old while surviving the direct impact from flying rubble. These include an awesome large armoured sea cucumber and large snails such as Tridacna and spider cowries.
• swelling and shrinking: an age-old protection mechanism is that of swelling when times are right and shrinking when they are not. Anemones, soft corals, tube corals and some sea cucumbers use this method to protect themselves.
• covering with sand: if one is not able to burrow, a cover of sand suffices as protection against sand blasting or being rough-handled by turbulent water. We've seen it used by algae and sea cucumbers.
• being flexible: rather than being hard and brittle like reef-building corals, there are many softer or leathery corals that survive hurricanes better.

Hurricanes Hurricanes or tropical cyclones as they are called in our area of the world, do not strike frequently (Niue 1959, 1960, 1970, 1989, 1990, 2004) and therefore it is hard to believe that they have such a pronounced effect on the underwater environment. Not only do they affect the visual aspect of the seascape, but we observed that they also affect the structure of the cemented coral rocks that built Niue, and that they have been doing this for as long as Niue exists (1-3 million years). However, no scientific proof is yet available. The map shows where hurricanes strike most frequently and the paths they take. New Zealand used to be struck frequently in the past, but for some time now, has not experienced any (Cyclone Bola 1983, Ola 1993). Cyclones are born over warm water and they dissipate over land and over cold water while raining down their amassed moisture.

When hurricanes travel in one direction for some time, they send large waves ahead that have a low frequency and high speed. Such waves reach deep and their destructive power exceeds normal storm waves by far. Thus hurricanes leave unerasable marks by creating barren areas. One would have thought that the barrens will recover, but this is only partly so. Immediately after denudation, the surface becomes covered in fine algae that prevent other animals, like young corals from settling there. Then the grazing armies of snails, sea urchins and fish take over, removing both algae and whoever tries to settle there. So the barren areas are a stable habitat form, comparable to the grasslands of the Serengeti. Only now and then a large storm is needed to keep them barren. The red band on the map shows where Cyclone Heta caused its damage, but other cyclones may arrive more from the NW, causing more damage to Avatele in the south and less to Uluvehi in the north.

Underneath the fine algae grows another algal form, a coralline alga known as pink paint. It grows flat leaves on the rock although these are not true leaves like green plants have. These coralline leaves are almost as hard as a coral skeleton, and over time they form reefs almost indistinguishable from those built by corals. In fact, most coral rocks contain a high ratio of coralline algae. The coralline algae grow over anything and everything, and in doing so encapsulate corals and coral debris. When the temperature becomes too low for corals (as during the ice ages), the coralline algae will still grow but perhaps insufficiently to build reefs. We have observed that the coral rocks of the Alofi Terrace on the hurricane side, are of this type: jumbled and erratic (see also Niue's geology).
 
 

f220431: a clump of brain corals encapsulated with other corals and debris into a coralline matrix with a jumbled structure. f220433: the sea has broken through the jumbled rock, providing a glimpse of a cross-section through the Alofi Terrace at Alofi on the hurricane side. Notice the platforms, walls, cavities and some brown soil formation. It even shows some dripstone and vertical percolation channels.

f044036: apart from the leafy Porites corals in the foreground, the rest of the rock shown here consists entirely of pink paint, a reef-building coralline alga.

f044005: this rock face at Avatele was hit twenty years ago and encrusting Porites corals begin to muscle in over the dominant pink paint - until the next cyclone strikes.

From the chapters above, it is clear that Niue is not able to catch the fishes found around continents with continental shelves. Drawing a net through the water may well cost more energy than the catch can pay for. So, longlining for predatory fish is Niue's remaining option and judging from the experience of local fishermen, this may well be possible on a large scale further out over the entire EEZ of Niue. As mentioned before, scientists are puzzled over the unexpected density of large predators in these infertile seas. But some good information is available. Niue's EEZ counts ten sea mounts, and these stir the water as the tide wave passes by, resulting in some upwelling. However, most of these sea mounts are too deep to account for this effect and some seamount fisheries have collapsed elsewhere (see more detailed map [2]).

f221403: the harvest of two hours of early dawn trolling with four baited lines. Two yellowfin tunas and two albacore tunas. Where do they come from and what do they eat?

f220827: although Niueans do not swim well, many are skillful fishers from their canoes. During one competition, they landed a 90kg yellowfin tuna, a large shark and a large striped marlin. Imagine a fight with these on a hand line from a wobbly canoe!

The density of fish over seamounts that somehow attracts them, depends on [1]:

• size and shape of seabottom discontinuity: the larger and the higher the discontinuity of the sea bottom, the more the tide wave will be distorted, resulting in stronger currents over larger distances. The orientation of the discontinuity is also important. If a ridge or canyon lies across the direction of the tidal wave, more turbulence can be expected. The map of sea mounts suggests that the area close to Niue is likely to provide such a discontinuity, since it is both large and located across the tide wave.
• tidal amplitude: the larger the tide wave, the larger its effect and the more water is stirred. Refer to the geography chapter for Niue's bathymetry (shape of the sea bottom) and its place in the spider web of rotating tide waves. Niue's tide is about 1m, which is half of the maximum experienced in the open Pacific Ocean. Only closer to indented coasts will it become larger.
• depth of the top of the sea mount: the closer the discontinuity is to the surface of the water, the more mixing will reach sun-lit depths for adequate plankton growth. Deep ocean mixing does not contribute to productivity. Most of Niue's seamounts are too deep.
• distance to coast: coasts provide nutrient rich waters and schooling prey fish on which predators prey. Such schools may wander off into the open ocean, and following them, their predators. Thus the closer to a large shore, the more fish. However, Niue is very far from any such shore.
• productivity of surrounding waters: the nearest centre of productivity lies northward into the tongue of cool water where Coriolis forces cause upwelling eddies. Predator and prey fish may wander out of this productivity centre.
• distance to other concentrated areas: the nearer to an area of productivity, the more fish can be expected. Niue is located in a patch of clear, unproductive water and currents bring in more of such water from the central part of the South Pacific.
• sea currents: sea currents bring food towards fish that congregate and stay around sea mounts. The sea currents around Niue and its seamounts are not known. Satellite maps suggest a tradewind-propelled current towards the NW.

The quantities are green productivity, which on land leads to crops directly and to livestock one step away (trophic level) with biomass losses to wastes and energy for heating, movement and internal transport (breathing, blood circulation). As a rule of thumb, each next trophic level contains less biomass, usually 6-10 times less. In the sea where life begins with microscopic plants (phytoplankton), it takes 3-5 trophic levels before fish are large enough to be eaten by humans (table fish). Thus biomass and productivity at this level is about 100 times less. The continental shelf for instance is estimated to produce 2-6t/km2 of edible fish. The open ocean accounts for less again, with a high degree of uncertainty.

Estimates for the kind of sustainable harvests that can be expected from Niue's EEZ are:

• New Zealand earns $1.2 billion annual export value caught mainly over a continental shelf of  240,000km2, or $5000 per km2. If Niue's EEZ is 50 times less productive (a reasonable estimate) then for its 390,000km2 EEZ, earnings up to $39 million in exports could be earned.
• [other calculations waiting for further information]

But Niue does not have a safe harbour, so fishing boats must be small enough to be lifted out of the water. For such boats to stay far out for prolonged periods, storing ice and catch while travelling fast and economically, and also light enough to be lifted out of the water, requires novel ship designs.

The fish expected between 500-900m depth are: alfonsino (Beryx splendens), bluenose grouper (Hyperoglyphe antarctica), pelagic armourhead (Pseudopentaceros richardsoni), barracuta (Rexea antefurcata) and small sharks (Squalus spp, Centrophorus spp, Etmopterus spp) [2].
Deeper down the roundnose grenadier (Coryphaenoides rupestris) can be caught to depths of 1200-2000m, but the deeper fish are all very slow growing and do not easily support a sustainable fishery. Besides, their flesh tends to be watery.

[1] Floor Anthoni (2004): Deductions from oceanographic knowledge and facts, however not proved by scientific method.
[2] Satellite bathymetry survey of the EEZ of Niue. Seafloor Imaging Inc. Govt of Niue, MAFF.
Read about our most recent discoveries about symbiotic decomposition and mixotrophy which explain why the productivity of the deep blue sea around Niue can be much higher than originally estimated. Visit the Dark Decay Assay chapter.