Kermadec Islands - images of corals, gorgonians and anemones

By Dr J Floor Anthoni, 2002

For New Zealanders, the Kermadecs are interesting because the seascape is dominated by corals rather than large seaweeds. This section shows the variety in coelentherates (flower animals) found there, ranging from sun-loving corals to gorgonians and anemones. The reef-building corals live in symbiosis with algal cells within their skins. These microscopic plants produce food from sunlight, by which the polyp's wastes are recycled. Many of the corals found at the Kermadecs are leathery to fleshy rather than hard.


The reef building corals are unique in the animal world because they embody within their tissues, a single-celled alga (zooxanthella), which means that animal and plant have been united inside the same body (hermatypic). This quirk of nature allows them to short-circuit the food chain in favour of an extremely efficient metabolism. For them the food chain goes direct from sunlight + nutrients = algal growth = energy and proteins for living. The circle is closed by the algae recycling the animal's wastes, assited by bacteria. This most efficient food cycle allows the coral polyp to live in clear waters with low nutrient concentrations and even less zooplankton. In the process, it is also capable of excreting massive limestone skeletons, the basis of coral reefs. But in order for such hermatypic corals to thrive, they need sunlight, and plenty of it. As a result, they are found close to the surface, where their hard limestone skeletons protect them from destruction by waves. To make it all work, the coral animal needs to be translucent to allow all light to reach the algae, and the algae have plant-like colours, which makes the world of hermatypic corals look rather drab yellow, brown and greenish.

Note that we have recently discovered the principle of symbiotic decomposition which makes a mysterious biomass, named slush by us, available as a source of nutrients, carbondioxide and hydrogen ions. By nurturing decomposing bacteria on their skins, corals can thus be extremely productive in apparently clear 'desert' seas, devoid of nutrients and plankton. Read more about these discoveries in the DDA section.
At the Kermadecs, one also finds strange fleshy corals, which also appear to need sunlight, but less of it than the hermatypic corals. For instance, one does not find them deeper than 30m, where normal plant growth would also stagnate. These do not build hard skeletons.

Under overhangs, and in caves, and deeper than 40m, one finds a colourful world of ahermatypic corals, that grow slowly without sunlight. For them the food chain is one step longer, and far less efficient since they need to expend energy for catching their food: sunlight + nutrients = phytoplankton = 10% zooplankton = energy + proteins for living - energy for catching. Catching the zooplankton means that there is substantially less food for them. Still, they are capable of building horny skeletons (gorgonians) or even limestone ones (cup corals and tube corals).

Note that the corals found here, live at the cold margin of the coral kingdom, and are therefore unsuccessful in accumulating coral reefs as they do in the warmer tropics. The number of species decreases rapidly in the 200km from Raoul (about 40 species) to l'Esperance Rock (about 10 species). Their density also decreases spectacularly, partly also because much soft rock is found further south.

We regret not being able to show closeups of the reef building corals, since expedition time would not allow for this. Many corals have symbiotic relationships with other animals such as small lobsters, shrimps, clams and more. Closeups would have revealed such interesting details. Also many corals remain nameless, until we are able to identify them. For coral closeups, visit the underwater world of Niue which has about 200 coral species.

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f031028: various reef building corals
f031028: About 2-6m deep, one finds a kaleidoscope of hard corals, separated by red and green algae. On closer inspection there are only few species. Their forms can be described as 'cauliflower' and 'broccoli', since similarly, they try to pack the most life into the least space, while absorbing the most light. Notice their typical drab colours.
f031422: plate corals on nearly barren rock
f031422: A hard rock composed of basalt, is scantily clad in plate corals. In the middle foreground a large patch of bare grey rock, where likely a plate coral once grew. Notice how these corals expand outward over existing growth, without actually attaching to the rock. They are thus relatively easily removed by strong waves. 

f032000: a solitary plate coral on a barren rock
f032000: A large plate coral sits like a cow pat on a bare soft volcanic rock. In the centre it grows upward in what looks like nipples. On closer inspection, these nipples appear to be barnacles, embedded inside the coral tissue. Where the coral is young at its outer rim, no barnacles are found, but they establish themselves later. It suggests that the coral did not grow over a barnacle colony but that the barnacles appeared later, and that they may have a symbiontic relationship. For it to work, the barnacles must be able to grow as old as the coral, which is unusual.
f032001: detail of plate coral
closeup of barnacles

f031106: shagpile coral and toadstool grouper
f031106: The shagpile coral (Hydnopora sp.) grows like a plate coral, over the surface, but it has the habit of starting on a pinnacle, and draping itself over the object as it grows. Who knows, a treasure chest may be found underneath? The toadstool grouper found sleeping here, may well have spent its youth hiding underneath the shagpile cloak, like many small fishes do.
f030905: the long tentacles of the shagpile coral
f030905: The long polyps of the shagpile coral resemble a bunch of optical fibres. They are extended day and night, and are somehow not grazed by other organisms. What is their secret?

f030907: soft coral
f030907: One of the fleshy coral species grows outward and upward from a small holdfast on the rock, thereby leaving space available for organisms with a lower profile. It cannot resist wave action as well as the hard corals, and grows deeper down (4-20m). This particular species likes to live just under the zone of hard corals.
f030908: detail of soft coral
f030908: A close-up of the same coral shows its fleshy fingers and small polyps. We had expected these corals to extend by night, like some tropical soft corals do, but this is about their maximum. However, they are able to shrink in averse conditions, which helps them to survive strong wave action. 

f030914: soft cabbage coral
f030914: Some of the fleshy corals have peculiar shapes, resembling desert plants.
f031103: fruit bowl coral
f031103: The fruit bowl coral (Turbinaria sp.), as we named it, stands as a solitary coral in sheltering depths of 10m or more. It is easily damaged by an anchor chain. The age of such a coral is unknown, but don't be surprised if this one is over 25 years old.

f031233: detail of coral polyps
f031233: It is not only the shagpile coral which has long polyps, but at least three other encrusting species have tentacles of varying lengths. Among such tentacles, other vulnerable species may find protection.
f031323: a large purple gorgonian
f031323: Large fan corals like this purple gorgonian, are rare because of their age (50 years?). Finding one as large as this, is always the highlight of a dive.

f031501: young purple gorgonians
f031501: A young purple fan coral started its life on a sponge-covered rock wall inside a large cave. Here it will be able to compete for space with other similarly slow growing organisms.
f031502: yellow zoanthid anemones on gorgonian frame
f031502: Immediately above the previous picture, a purple fan coral has been raided by an invasive anemone, a yellow zoanthid, who now dominates the entire fan. It killed the original coral polyps by just growing over them and smothering them to death.

f031505: orange gorgonian
f031505: The ceiling of the cave is even more protected than its side walls, reason why the most fragile organisms are found here. In the centre a fragile orange-pink fan, surrounded by yellow tube corals (Tubastrea sp.). Looking like individual anemones, these very slowly build limestone tubes in which they can withdraw. Behind the orange fan, top-centre a deceased fan, covered in sponges and seasquirts.
f031508: yellow gorgonian
f031508: The yellow gorgonian is much rarer than the others. In the foreground of both pictures the common brown featherstar. This seastar has specialised in catching minute planktonic organisms in its finely feathered arms.

f031506: yellow tube corals and purple gorgonian
f031506: Brown and yellow featherstars surrounded by yellow tube coral, and in the centre a young purple fan coral.
f031218: green tube coral
f031218: These green anemones (Dendrophyllia sp.) are in fact also tube building corals, forming small 'trees'. However, unlike the yellow variety shown left, these are found only in the light, usually on steep rock faces, which suggests that they too have green algae in their tissues.

f031814: red actinia anemones
f031814: A cluster of horse anemones  wandering anemones(Actinia sp.Phlyctenanthus sp.), living close to the surface in wave-swept conditions. Top left, an unusual triplefin can be detected, see right

f031814b: enlargement of unidentified fish on left photo .
Note! The above red anemones i thought were horse anemones of the Actinia genus but Michela Mitchell from put me right,  noticing these were wandering anemones of the unusual Phlyctenanthus genus.. What an amazing power of observation!!