The sea urchins found on the rocky shore, are all grazers. With their five teeth, they graze the rocks. This at the same time encourages colonisation by sessile organisms, and also removes them. Those that can evade the urchins, have a chance to establish. Those that are too hard to eat, like corals, can survive too. Thus the urchins have a major influence on the rocky shore habitat.

The large starfish like the seven-armed stars, are hunters. They can move fast and have a good sense of smell. By eating some grazers, they too can have a decisive impact on the composition of the community.
The crown-of-thorns starfish has specialised in eating hard corals. It does so slowly, but with certainty, leaving a swath of dead white corals behind. Although their numbers aren't worrisome, their impact on the Kermadec coral community is decisive. By eating fast growing species, they make room for slow growing ones. They also make the coral community more patchy and varied.
A black cushion star lives in wave-washed environments where others cannot survive the rolling of stones. We have no photos of it, and neither of the black nerita snail Nerita atramentosa, living one zone above it.

The feather stars do not influence their environment. They just sit in their niches, stretching their feathery arms out in the moving water, and catching plankton.

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f031406: Brown urchins (Heliocidaris tuberculata) are found in the same areas as the purple urchin and the pied urchin, but they appear to prefer wave-washed habitat.

f031406: Enlargement of previous photo to show the features of the brown urchin.

f031804: At Macdonalds Rock, the swell is very powerful, but not powerful enough to brush these strong purple urchins (Centrostephanus rodgersi) from their perches. But in order to stay put, they hide in cracks, depressions and under overhangs.

f031824: The whole area of hard rock is covered in pink paint (Lithothamnia sp.), which is a hardy red alga. On left a purple urchin and on right a Kermadec top shell. The urchin  folded its spines in such a way as to cause least drag.

f030424: Although the purple urchin looks jet-black from even a short distance, it is nonetheless dark purple when lit by a powerful light.

f030925: A rare urchin similar to the purple urchin, can be found hiding in caves.

f030901: The pied urchin or white-spined urchin (Tripneustes gratilla) is truly jet-black with purely white spines. It is very common on the Kermadecs.

f030909: A fine close-up of the pied urchin shows its five-sided radial symmetry.

f031204: The diadema needle urchin (Diadema palmeri) is one of the finest showpieces among sea urchins. This young one still has its white lobes with white spines, which will darken as it ages.

f031205: Close-up of a young diadema urchin. Notice how sharp its spines are. These urchins have no natural predators because they can defend themselves perfectly. Their spines are very sensitive to water motion, and very mobile as well.- and somewhat poisonous.

f031115: Diadema urchins can be found on the sand, under overhangs, or near the corals where they once hid while very small. They have their own patches, to which they return after foraging by night.

f031117: Close-up of two urchins shown in previous photo. Needle urchins can fold their spines to enter small openings. Amazingly they can still creep out.

f031815: The pencil urchin (Phyllacanthus imperialis) remains hidden by night and day. It is not known what it feeds on.

f031006: A crown of thorns star (Acanthaster planci) has adapted its stomach to feed on many coral polyps in a single sitting. It cannot reach the shallow water corals, because it attaches only weakly to the substrate. In the distance the white dead corals it dined on before.

f031109: The crown of thorns star (COT star) found at the Kermadecs is rather beautiful, and has a soft puffy body. Although its spines are not sharp, allowing it to be handled with care, the slightest scratch or wound can cause severe swellings because they are poisonous. Note that this star has 15 arms!

f030904: Side view of a COT star.

f031110: Close-up of the Crown of thorns star, showing concentric rings of red tubefeet. The red colour is caused by red tube feet, sticking up through thousands of pores in its back. These tubefeet keep it free from being fouled by algae and other animals.

f031202: Macro close-up of a COT star's back. The small red tubefeet and their pink pores can clearly be seen. Top left is the porous disc through which the animal filters the water needed for its internal hydraulic systems.

f032006: The black seven-armed star (Astrostole sp.) is common where small snails such as the Kermadec nerita (Nerita atramentosa). Top right the common Kermadec barnacle (Tesseropora sp.) on which it perhaps also feeds .

f031822: The mottled seven-armed star (Astrostole sp.), could well be the same species as the black seven-armed star, but it is more slender and found in a different habitat, surrounded by sea urchins, on which it perhaps feeds.

f031808: The brown seven-armed star (Astrostole sp.) is much more slender than its black cousin, and may well be a separate species.

f031809: Close-up of the brown seven-armed star. Notice its very rough back very densely covered in strong and sticky tubefeet, which is common to all Astrostole species.

f031232: This orange star we named the gingerbread star, because of its resemblance to baked gingerbread men. It is common at the Kermadecs.

f031806: An unknown orange star with tubular legs, of which some are shorter than others. It is possible that this star is hunted by a large snail, and in order to escape, sacrifices a leg. This later regrows to its normal size. Such behaviour is observed with the large carnivorous trumpet snails, such as the Charonia lampas rubicunda found in NZ.

f030932: These brown and yellow feather stars are commonly seen, wherever the animal can hide behind an obstacle. The tips of its feathers are often eaten by some other animal, as shown in the foremost feather.

f031506: The yellow feather stars add a festive note to the decorations found on rock walls and under overhangs. The feather stars of the Kermadecs are more straight than their relatives found in NZ.

f031507: A large bunch of feathers, originating from no more than three feather stars. They can move about freely, but prefer to huddle together. With their sticky tubefeet, invisibly small, they catch small planktonic organisms, which are transported to the mouth on a slime conveyor in the centre 'pen' of each feather.